Reply
 
Thread Tools Display Modes
  #1   Report Post  
Posted to rec.audio.tubes
[email protected] themend@gmail.com is offline
external usenet poster
 
Posts: 18
Default Restoring a Sherwood S-5000

Hello all,

One of my favorite tube amps has to be the Sherwood S-5000. It's a little gem of an integrated amp that is quite easily underestimated. Most people would put it in the same class as a Scott 299, also a 6BQ5 amp, although the Sherwood is really a 7189 amp, and actually uses the higher plate voltage possible with the 7189. It also has larger output transformers, and manages to put out 24w RMS per channel.

The pre-amp section, despite having dated ideas about tone control and Fletcher-Munson curves (thankfully switchable) maintains a very neutral and open sound. The bass and treble knobs are actually usable and helpful at times, and don't have some insane Q that belies their center frequency. The phono section is startlingly good so long as the original Telefunken 12AX7s are occupying the two sockets in the phono section. There are a handful of other tubes that can work there as well, but filament hum and microphonics plague any U.S. made 12AX7 or 7025 I have ever tried in this amp, shield or no.

The use of 7199 tubes as the phase splitter/driver tubes is somewhat unfortunate since they are hard to obtain these days. The upshot is that they seem to last a very long time in this circuit, and they sound quite good. Some have attempted to use 6GH8A in this position, or modern Russian 7199 that are actually re-pinned 6GH8A, and I would strongly discourage that. They don't sound right at all. Just ask the ST-70 crowd. You'd have to modify the circuit, and I think that in this case, that's just daft. The 7199 last too long and sound too good to make that a useful mod, IMHO.

In this thread, I will be going over the basic steps of reviving a Sherwood S-5000 as I rebuild yet another one of these beauties. This is more or less your standard re-cap job, plus replacing the selenium rectifier in the bias supply. There are however some things that are specific to this amp, little tricks for dealing with the tight chassis space, and other stuff too. The way capacitors are mounted in this amp is a real pain. It uses twist-lock can caps, one of which is mounted at a 35 degree angle.

If -YOU- have an S-5000 or S-4400 and you have any questions about it, please feel free to ask away and I will cover the topic in this thread. I've dealt with just about everything there is do deal with on these amps, as this will be the 6th one I've restored. The S-5000II is a totally different beast using 7591s, and I will not be covering that amp here.

Still trying to figure out where I will post pics and schematics so I can post links here, so give me a little while on that.

For those of you exclusively into DIY, the S-5000 circuit is a very cool and sweet sounding 7189 amp. It's the only amp I've seen that gets 24 watts out of a pair of 7189s. I've made one using the Triode Electronics ST-70 board as a front-end and the result was so good that it sold for $1000 despite being a prototype and not terribly well built. It was in a Hammond box as I recall, but I did engine turn the top at least. So we can also discuss DIY around this circuit in this thread if anyone wants.

This is my favorite vintage amp of all time, so I can talk about it endlessly without getting bored.

Feel free to ask away as I prepare some pics and schematics to get this started.


-forkinthesocket

  #2   Report Post  
Posted to rec.audio.tubes
[email protected] themend@gmail.com is offline
external usenet poster
 
Posts: 18
Default Restoring a Sherwood S-5000


Ok, pics coming soon...

First step was to take voltage measurements off the bias and HV+ rails. Here's what I got on my S-5000. By the way, there are two variants of the S-5000 that I will discuss later, basically the older, longer version and the newer, shorter version. The one I am working on here is one of the shorter types.

After the 20uf cap coming off the rectifier, there is a 33 ohm 7w resistor connecting to the next cap section, [email protected] According to documentation, this point should measure 415v (plate) but I often find that it reads higher. This particular amp is currently measuring 438v on the plates! This is why you really have to have a 7189 here, or at least a beefy 6BQ5 that is known to handle high plate voltages. I've seen lesser Sovteks arc over in these amps before.

So, according to my Sams photofact, the correct voltages going down the HV+ rail are as follows on the left, and this amp is as follows on the right:

Photofact This S-5000

C1/A - 420v 442v
C1/B - 415v 438v
C1/C - 350v 365v
C2/A - 275v 285v
C2/B - 225v 204v

So right off the bat something looks amiss - All these voltages are a bit higher than listed, but that is ok. What is odd is that they're all higher except for one, which is quite a bit lower. That second section of C2 should be higher than 225v, since everything else is higher than listed. Instead, it's 21 volts lower than listed. I suspect this points to either that dropping resistor or that cap section being leaky. Either that, or current draw after that dropping resistor is higher than it's supposed to be for some reason. We'll have to get to the bottom of that.

Now on to the bias supply. It's interesting to note that the bias supply also supplies DC filament current to the two phono preamp tubes, which makes it even more interesting that I've never gotten a US made 12AX7 to sound good in those positions, getting hum regardless. I suppose it means that it was more induced hum from the surroundings than from the filaments as I had stated earlier, or perhaps there was something amiss in the amp in which I tried it. I will have to re-visit that whole thing once this is finished..

There are no real test points listed in the bias supply other than the final ouptut voltage, which is supposed to be -20v. This amp is currently putting out -21.8, which is probably right on target considering the plate voltage is running a tad high - the extra bias voltage is welcome. In fact, I'd like to see it a little higher, and once the selenium rectifier is swapped out for silicon diodes, I'll expect to see closer to -23v. A real indication of the health of this circuit will be the DC voltages at the phono tubes, since these actually have some current draw to them

Sam's Photofact This S-5000

C3/A - Unlisted -29.3v
C3/B - 24v 22.74v
C3/C - -20v -21.8v
V1 Fil - 24v 22.74
V2 Fil - 12v 11.06


So the bias supply looks good, but the DC voltages to the phono preamp section looks a tad soft. Who knows, filament starving can have nice effects, but It'll be interesting to see what happens when the selenium rectifier and those electrolytics are replaced. I always see the bias voltage increase, so the filament should as well. This SAM's photofact has the polarity of the bias cap backwards, FYI. I will post it all soon when I figure out where to put all the uploads for this project.


It should be noted that this amp currently works and sounds fantastic. No signs of hum, very clean sound, no issues at all except the power transformer gets a little bit hotter than I think it should be. Thermal gun measurements have gotten close to 136F. My experience tells me that the second rev. of the S-5000, which this one is, tend to run a little hotter due to smaller iron. However, I still feel this one is a bit hotter than it should be after two hours of running and I think a power supply rebuild might lower that figure by 10 degrees. Still, for a bone-stock amp built in 1959, this thing is nothing short of amazing.

More to come soon!


-forkinthesocket
  #3   Report Post  
Posted to rec.audio.tubes
[email protected] themend@gmail.com is offline
external usenet poster
 
Posts: 18
Default Restoring a Sherwood S-5000

Ok, so I guess I can just share the photos and schamtics via dropbox.

https://www.dropbox.com/sh/y4j5cv5ro8o5yja/cvW9ncqTtV#/

Here's what's in there so far:

Pictures of the various twistlock can caps that are there
A picture of the underbelly of the amp
A picture of the unbelievably wrong Sam's photofact of the bias supply
A picture of the -Actual- Sherwood schematic right from a manual, applying to this second rev of Sherwood S-5000
A picture of the selenium rectifier which will be replaced


Regarding the voltages I measured in my last post, it is good to note that Sherwood has different voltages listed in their schematic. However, the Sams schematic is referring to the first rev. of the S-5000, the 'longer chassis' model. These two models can easily be distinguished visually, by the way. The newer one has all the 12AX7s up front mounted flat and underneath a square tube cage with slotted vents and a tube placement sticker. The old version has the preamp tubes at a 45 degree angle, with individual tube shields.

So, let's re-do that chart against the Sherwood schematic since I think that will be more in line with reality in this particular amp. FYI, the Sams schematic has some SERIOUS errors in the bias section, mainly that the capacitors and diodes are in there backwards. Their version magically produces negative volts from positive diodes and caps. Sheesh. So that should never be used for anything.

Sherwood Schematic This S-5000

C53/A - unlisted 442v
C53/B - 425v 438v
C53/C - 350v 365v
C24/A - 270v 285v
C24/B - 250v 204v


That is very telling. We see that the plate voltage is much closer to being 'in-spec' than before, though it is still a tad high, I recall that always being the case in these amps. Nevertheless, we have even more of a problem now in the second section of C24, as we are now 46v shy of the listed value. This is looking even more like a real problem than it did before. Also note that Sherwood calls these two caps C53 and C24, where Sams calls them C1 & C2, which is probably a more logical choice. Nevertheless, from here on out I will refer to the Sherwood schematic. If somebody wants to discuss an older chassis, we can do that too...

I think that's all for today, though I might get around to replacing the selenium rectifier.


-forkinthesocket
  #4   Report Post  
Posted to rec.audio.tubes
[email protected] themend@gmail.com is offline
external usenet poster
 
Posts: 18
Default Restoring a Sherwood S-5000

Hello all,

Made some progress on the bias supply yesterday, but didn't get around to posting it. First, the selenium rectifier he
https://www.dropbox.com/s/27opjx5auy..._Rectifier.jpg

has been replaced with a pair diodes and a pair of caps mounted to a terminal strip as seen he
https://www.dropbox.com/s/bfynay796k...eplacement.jpg

There is nothing special about these diodes, they are rated for 1000v (total overkill) and 1.5 amps. Since silicone diodes tend to generate a bit of switching noise, two [email protected] mica caps have been added to shunt that noise to ground. While the center post of this terminal strip is mounted to the chassis, I find that using that mechanical connection as a ground can be hit and miss, so instead, I run a ground wire inside the chassis and solder it to the bottom of a cap can. Here is the diode bridge installed in the amp where the selenium rectifier once was:

https://www.dropbox.com/s/nzy9mw08cq..._installed.jpg

"But wait!", you say "Aren't you going to replace the capacitor cans?" Well, yes we are. But we are only going to replace the two HV+ capacitors, and while we will also replace the caps in the bias supply, we will not remove the old capacitor can. Why? Because it is a very rare capacitor can with COMMON POSITIVE. All other can caps are common negative, and you simply will not find a replacement for this bias supply can. So, we will have to rebuild the bias supply using axial and/or radial caps stuffed underneath the amp. Don't worry, there's room as we'll see later. For now solder the ground to an unused common terminal on the bias cap can as I did with the green wire he

https://www.dropbox.com/s/1knvs3qlc6...for_diodes.jpg

In order to mount the new diode bridge, I first had to cut 7/8" off the old mounting bolt for the selenium rectifier in order to use it. I just used the bolt cutter on my strippers. Check it out:

https://www.dropbox.com/s/eqwe6e7vgf..._off_screw.jpg

Ok, so I got all that done, now it's time to fire up the amp and take measurements. Oh crap! One of the output tubes is arcing over now! Better get the tester out!

After testing my output tubes, it turns out that it was a complete coincidence. One of the tubes had already had a part come loose inside, and all I had to do was operate the amp upside down to make the short happen. After testing, 3 tubes flunked the test. One arcs over, the other tests with shorts, and the last one is weak. Dang, and they're all Amperex Bugle Boys..... Anyway, after digging through my stash, I found a replacement for these three guys he

https://www.dropbox.com/s/y1suozb1di..._bad_tubes.jpg

Ok, now the amp fires up without any drama. As I expected before, my bias voltage has now risen up and is now -24.85v, about where I expect it to be with silicon diodes and no dropping resistor. Yes, you can get a couple more watts out of this thing with a lower bias, but the wear and tear on the output tubes and the heat generated makes it scarcely worth it, IMHO.

The DC filament voltages are now 26.1 and 12.7 volts at V2 and V1 respectively, up from 11.06 and 22.74. These might be just a touch high, but they're within the realm of sane. I may in fact try to put a slightly higher value dropping resistor in front of these.

I have also made some interesting observations regarding the voltages listed on the schematics, versus real life and I will get to that in my next post.
  #5   Report Post  
Posted to rec.audio.tubes
[email protected] vwmicrobus@gmail.com is offline
external usenet poster
 
Posts: 5
Default Restoring a Sherwood S-5000

On Sunday, January 12, 2014 2:52:54 PM UTC-5, wrote:
Hello all, One of my favorite tube amps has to be the Sherwood S-5000. ....

-forkinthesocket

Thank you for the weath of info! I happen to have an S-5000 that I love. It has a hum in the phono preamp though.. something I would like to get rid of. I really like how you can vary the loudness curve by adjusting the preamp volume along with the master volume, that plus the tone controls gives me plenty of ability to get the sound I want at any level. A very well thought out amp. The selector switch allows stereo, reverse stereo, mono channel A, mono B, & mono A+B plus, pulling out the balance knob changes the phase on one channel. Very flexible!
Here is a video of me testing it out when I first got it:
http://youtu.be/pRzVHkyYUso
It is now in my listening room connected to a set of vintage Warfedale speakers..

--JRC


  #6   Report Post  
Posted to rec.audio.tubes
[email protected] themend@gmail.com is offline
external usenet poster
 
Posts: 18
Default Restoring a Sherwood S-5000

Hi there!

Cool to see you here! I remember that video on YouTube! Man, what a fantastic rig you have behind it.

Looks like you have a later version of the S-5000 that I refer to as the short chassis, which is also the one I am working on here. From the video it looks like some work has been done on it already, notably the bias supply rectifier looks to have been replaced. We should also check the date codes on the capacitors to see what has and has not yet been done.

So far in this thread, I have measured the HV+ rail, and the bias+phono filament supply. Then, I replaced the selenium rectifier with an odd little arrangement of diodes and caps that I will explain later... Usually folks use one cap to hush the diode noise, I now use three; two at the diodes from their inputs to ground, and one on the bias voltage wire at the junction with the first electrolytic filter cap. That last one hasn't been added in my amp yet since that junction is going to be done along with the filter caps.

So, when you have a chance, check out those voltages (be careful, these are HIGH voltages) and post your results. Also, I am curious to see what make of tubes you have in your phono section, or for that matter the whole amp. From the top front of the amp, these will be the first two tubes, from left to right. They're directly behind the selector and balance knobs. If you're not sure what make they are, snap pictures of them. I am interested to see if they are Telefunken or not.

Good luck and let me know if you have any questions or issues. Oh, and welcome to RAT, by the way.

-forkinthesocket
  #7   Report Post  
Posted to rec.audio.tubes
[email protected] themend@gmail.com is offline
external usenet poster
 
Posts: 18
Default Restoring a Sherwood S-5000

While we wait to hear from JRC, let's go over the parts list for the rebuild.

First, let's talk about the large twistlock cap right behind the output tube section. This is the main filter capacitor for the HV+ supply, and it takes the brunt of the wear in the power supply. The reason for this is mainly because the capacitor is located in a spot which positively guarantees that it will get baked by the output tubes. Here is a picture of it:

https://www.dropbox.com/s/2lq2ltcke4gt11w/S-5000_C1.jpg

It's also peculiar in that it is mounted at an angle, just as the power tubes are, which is what gives this amplifier such a low height. There are a few schools of thought on twistlocks like these. Some people prefer to cut them open from the bottom, gut them, and stuff them with new radial or axial caps. The other notion is to simply put those same caps underneath the amp and re-wire everything to accommodate that. Some feel replacing the whole can is best when there are replacements available. Lastly, some people feel that they can magically 'reform' capacitors by doing some sort of rain dance with a variac. As you may have guessed, I do not fall into that last group of people.

While there probably are certain capacitors in certain amps that may respond to such a thing, this particular cap in this spot sees too much voltage and too much heat not to be somewhat degraded by now. Some of these S-5000s were never ran with the cover, since the cover was an additional cost; not included with the amplifier purchase. Lots of these were placed into consoles and the like and so did not build up all that much heat. These ones can often sound OK with the original cap. The S-5000 running inside its cover, especially a leatherette covered one will just cook away in there. These almost always have noticeable hum when played.

If we look underneath the cap he

https://www.dropbox.com/s/pefyhgh7l6...onnections.jpg

We see that there isn't a whole lot of room for adding caps underneath, without resorting to putting them in odd places, and adding new wires and terminal strips. So really, our best options are to either replace the can or stuff it with new caps. Since there are very good replacements available from CE, I suggest the extra money spend on this:

http://www.tubesandmore.com/products/C-EC4020X2-525

Is well worth it, especially considering the effort in re-stuffing a capacitor. Note that this capacitor is a 40/40/20/20 sectioned cap at 525v. The original Sherwood design called for a 20/40/40/5 sectioned cap at 500v for the first three sections, and 350 volts for the 5uf section. This CE cap is physically the same dimensions as the Sherwood cap, offers 25 more working volts, and gives us an extra 15uf on one section. As long as we are careful to wire the 20uf section to the 5AR4 rectifier, this cap is an ideal replacement.

Speaking of the 5AR4 and 20uf, there is a reason you must not increase the value of this particular cap. Tube rectifiers have a maximum capacitance that can be directly connected to the output. Those values are usually listed in tube manuals. If you add more here, the rectifier will likely arc over due to the current draw. After the first dropping resistor, you can literally add as much capacitance as you want, as the current rush will now be limited by that resistor. It is possible, however, to introduce a resonance by altering the R-C time constant by doing this. I have seen one S-5000 that wound up with a very low frequency power supply oscillation as a result of an odd re-cap, it showed up as very pronounced woofer excursion at around .5hz, which one might think would be beyond the capability of the output transformers, but obviously not.

So, in this case, everything will retain its original values except for the last section which will increase to 20uf from 5. I personally feel that 40uf is just adequate for the first section off the dropping resistor. Depending on how the terminals of this cap are laid out, I may decide to use the additional 20uf section to increase the first 40uf section to 60uf, and simply add a 10 or 20uf cap underneath for that last section. Since I have not used this particular cap before, I will have to wait until I have it on hand to see if the terminals and distances underneath will allow this. In the past, I have used Aero-M capacitors for this part, and was able to add capacitance easily.

For the second twistlock capacitor, I'm going to try this:

http://www.tubesandmore.com/products/C-EC20-20-450

Here's the original in the amp:

https://www.dropbox.com/s/kvxfs3grlzzpqfw/S-5000_C2.jpg

This is interesting - last time I did one of these S-5000s, there were no fresh stock 1" twistlocks available. Here we have a 20/20 @450v that is the same dimensions as the stock capacitor! The stock cap is a 20/30 @ 400, so we get a higher voltage rating with this cap, but come up 10uf short. However, there is plenty of room underneath next to this cap to add another 10uf or more. So, I'm going to order one of these to find out if they're suitable.

Lastly, we have the oddball bias supply capacitor. It has a common positive can, something that I rarely see anywhere else but on Sherwood amps. Anyone else know of amps that use these? I'm curious! As a side note, if you are ever working on a Sherwood and you see a twistlock capacitor can that is covered in cardboard, that can has high voltage on it and that cardboard is there as an insulator. Be careful with those!! Luckily, they don't exist on the s-5000 but you see them a lot in later Sherwood amps.

Anyway, the bias cap... It's a 250/150/50 @ 50v cap, and the best bet is to just leave it in place, and use axials or radials underneath to replace it. We don't need to go crazy here with capacitance, maybe a -little- more on the bias supply to lower ripple, but the vaules here seem pretty acceptable in practice.

So that's the update for now... I'm going to order the parts tomorrow and we'll see next week how they work out.


-forkinthesocket





  #8   Report Post  
Posted to rec.audio.tubes
Andre Jute[_2_] Andre Jute[_2_] is offline
external usenet poster
 
Posts: 631
Default Restoring a Sherwood S-5000

Yo, Dorkinthesocket, if you're such a newbie that you don't even have a junk box with a couple of IN4xxx in it, like a proper experimenter, as we see in your other self-important post, you really want to start in electronics with something less dangerous than tube voltages. -- Andre Jute

On Thursday, January 16, 2014 12:55:25 AM UTC, wrote:
While we wait to hear from JRC, let's go over the parts list for the rebuild.



First, let's talk about the large twistlock cap right behind the output tube section. This is the main filter capacitor for the HV+ supply, and it takes the brunt of the wear in the power supply. The reason for this is mainly because the capacitor is located in a spot which positively guarantees that it will get baked by the output tubes. Here is a picture of it:



https://www.dropbox.com/s/2lq2ltcke4gt11w/S-5000_C1.jpg



It's also peculiar in that it is mounted at an angle, just as the power tubes are, which is what gives this amplifier such a low height. There are a few schools of thought on twistlocks like these. Some people prefer to cut them open from the bottom, gut them, and stuff them with new radial or axial caps. The other notion is to simply put those same caps underneath the amp and re-wire everything to accommodate that. Some feel replacing the whole can is best when there are replacements available. Lastly, some people feel that they can magically 'reform' capacitors by doing some sort of rain dance with a variac. As you may have guessed, I do not fall into that last group of people.



While there probably are certain capacitors in certain amps that may respond to such a thing, this particular cap in this spot sees too much voltage and too much heat not to be somewhat degraded by now. Some of these S-5000s were never ran with the cover, since the cover was an additional cost; not included with the amplifier purchase. Lots of these were placed into consoles and the like and so did not build up all that much heat. These ones can often sound OK with the original cap. The S-5000 running inside its cover, especially a leatherette covered one will just cook away in there. These almost always have noticeable hum when played.



If we look underneath the cap he



https://www.dropbox.com/s/pefyhgh7l6...onnections.jpg



We see that there isn't a whole lot of room for adding caps underneath, without resorting to putting them in odd places, and adding new wires and terminal strips. So really, our best options are to either replace the can or stuff it with new caps. Since there are very good replacements available from CE, I suggest the extra money spend on this:



http://www.tubesandmore.com/products/C-EC4020X2-525



Is well worth it, especially considering the effort in re-stuffing a capacitor. Note that this capacitor is a 40/40/20/20 sectioned cap at 525v. The original Sherwood design called for a 20/40/40/5 sectioned cap at 500v for the first three sections, and 350 volts for the 5uf section. This CE cap is physically the same dimensions as the Sherwood cap, offers 25 more working volts, and gives us an extra 15uf on one section. As long as we are careful to wire the 20uf section to the 5AR4 rectifier, this cap is an ideal replacement.



Speaking of the 5AR4 and 20uf, there is a reason you must not increase the value of this particular cap. Tube rectifiers have a maximum capacitance that can be directly connected to the output. Those values are usually listed in tube manuals. If you add more here, the rectifier will likely arc over due to the current draw. After the first dropping resistor, you can literally add as much capacitance as you want, as the current rush will now be limited by that resistor. It is possible, however, to introduce a resonance by altering the R-C time constant by doing this. I have seen one S-5000 that wound up with a very low frequency power supply oscillation as a result of an odd re-cap, it showed up as very pronounced woofer excursion at around .5hz, which one might think would be beyond the capability of the output transformers, but obviously not.



So, in this case, everything will retain its original values except for the last section which will increase to 20uf from 5. I personally feel that 40uf is just adequate for the first section off the dropping resistor. Depending on how the terminals of this cap are laid out, I may decide to use the additional 20uf section to increase the first 40uf section to 60uf, and simply add a 10 or 20uf cap underneath for that last section. Since I have not used this particular cap before, I will have to wait until I have it on hand to see if the terminals and distances underneath will allow this. In the past, I have used Aero-M capacitors for this part, and was able to add capacitance easily.



For the second twistlock capacitor, I'm going to try this:



http://www.tubesandmore.com/products/C-EC20-20-450



Here's the original in the amp:



https://www.dropbox.com/s/kvxfs3grlzzpqfw/S-5000_C2.jpg



This is interesting - last time I did one of these S-5000s, there were no fresh stock 1" twistlocks available. Here we have a 20/20 @450v that is the same dimensions as the stock capacitor! The stock cap is a 20/30 @ 400, so we get a higher voltage rating with this cap, but come up 10uf short. However, there is plenty of room underneath next to this cap to add another 10uf or more. So, I'm going to order one of these to find out if they're suitable.



Lastly, we have the oddball bias supply capacitor. It has a common positive can, something that I rarely see anywhere else but on Sherwood amps. Anyone else know of amps that use these? I'm curious! As a side note, if you are ever working on a Sherwood and you see a twistlock capacitor can that is covered in cardboard, that can has high voltage on it and that cardboard is there as an insulator. Be careful with those!! Luckily, they don't exist on the s-5000 but you see them a lot in later Sherwood amps.



Anyway, the bias cap... It's a 250/150/50 @ 50v cap, and the best bet is to just leave it in place, and use axials or radials underneath to replace it. We don't need to go crazy here with capacitance, maybe a -little- more on the bias supply to lower ripple, but the vaules here seem pretty acceptable in practice.



So that's the update for now... I'm going to order the parts tomorrow and we'll see next week how they work out.





-forkinthesocket

  #9   Report Post  
Posted to rec.audio.tubes
[email protected] vwmicrobus@gmail.com is offline
external usenet poster
 
Posts: 5
Default Restoring a Sherwood S-5000

ha.. wow.
Hey forkinthesocket..
I finally got my Sherwood, multimeter and a glass of SOCO in the same room... and my wife and kid in another room! Gonna be taking those measurements in the next hour or so. Will reply back tonight. so in the mean time, quit ****in on Andre's blarney stone and go write some more poetry...
whatever..
I greatly appreciate you sharing your knowledge on this particular amplifier!
it's just the kick in the ass I need to get mine working up to snuff.

--JRC
  #10   Report Post  
Posted to rec.audio.tubes
hugeshows hugeshows is offline
external usenet poster
 
Posts: 29
Default Restoring a Sherwood S-5000

Hey, cool I'm looking forward to it. Please upload some pics if you can, if you need a place to put them, PM me and I'll share my dropbox folder with you.

Cheers,

-forkinthesocket


On Saturday, January 18, 2014 8:25:17 PM UTC-5, wrote:
ha.. wow.

Hey forkinthesocket..

I finally got my Sherwood, multimeter and a glass of SOCO in the same room.. and my wife and kid in another room! Gonna be taking those measurements in the next hour or so. Will reply back tonight. so in the mean time, quit ****in on Andre's blarney stone and go write some more poetry...

whatever..

I greatly appreciate you sharing your knowledge on this particular amplifier!

it's just the kick in the ass I need to get mine working up to snuff.



--JRC




  #11   Report Post  
Posted to rec.audio.tubes
[email protected] vwmicrobus@gmail.com is offline
external usenet poster
 
Posts: 5
Default Restoring a Sherwood S-5000

OK, here are the stats. The main filter cap has been replaced with another can. Others have been replaced underneath.
Link to pics: https://www.dropbox.com/sh/zoqcrtzbmn1saha/JxXYbkaIIc

C1/a 472VDC
C1/b 470VDC
C1/c 388VDC
C2/a 301VDC
C2/b 217VDC
A lot higher than what you had, and what specs show! No wonder the 6BQ5's I originally tried for power amps were arcing.

There is an additional cap (see it in the C1 photo, to the right of the can) that has 46VDC on it.

Bias caps; These have been replaced, so my measurements are left to right as viewed in the pic:
-26.6vdc, -34.5vdc, -26.1vdc

As for the DC filiment voltages, the only one I found was 13.3VDC on the first two 12AX7's where is the 24V supposed to be?

Selineium rectumfryers have been replaced with diodes, see pic.

Tubes are as follows from the top, Left to right nearest the front: three Telefunken 12ax7, two Tesla ecc803s. Adjacent the filter cap are two RCA 7199.

I will note that the phono hum seemed to be less on my workbench than in the workshop that I am using the amp, not sure if that is because of smaller speakers, or lack of 8-ft flourescent lights above, or just power situations. But, it is still there. The amp is quite silent on FM input (used for my iPod)

--JRC


  #12   Report Post  
Posted to rec.audio.tubes
hugeshows hugeshows is offline
external usenet poster
 
Posts: 29
Default Restoring a Sherwood S-5000

Good god, those voltages are HIGH! Quick question - did you per chance take those measurements with the power tubes removed? That would explain why they are so high. If so, please take the measurements again with the power tubes installed. If not, what is your AC line voltage? Can you measure the AC HV coming off the transformer?


Thanks,

-forkinthesocket

On Saturday, January 18, 2014 9:53:18 PM UTC-5, wrote:
OK, here are the stats. The main filter cap has been replaced with another can. Others have been replaced underneath.

Link to pics: https://www.dropbox.com/sh/zoqcrtzbmn1saha/JxXYbkaIIc



C1/a 472VDC

C1/b 470VDC

C1/c 388VDC

C2/a 301VDC

C2/b 217VDC

A lot higher than what you had, and what specs show! No wonder the 6BQ5's I originally tried for power amps were arcing.



There is an additional cap (see it in the C1 photo, to the right of the can) that has 46VDC on it.



Bias caps; These have been replaced, so my measurements are left to right as viewed in the pic:

-26.6vdc, -34.5vdc, -26.1vdc



As for the DC filiment voltages, the only one I found was 13.3VDC on the first two 12AX7's where is the 24V supposed to be?



Selineium rectumfryers have been replaced with diodes, see pic.



Tubes are as follows from the top, Left to right nearest the front: three Telefunken 12ax7, two Tesla ecc803s. Adjacent the filter cap are two RCA 7199.



I will note that the phono hum seemed to be less on my workbench than in the workshop that I am using the amp, not sure if that is because of smaller speakers, or lack of 8-ft flourescent lights above, or just power situations. But, it is still there. The amp is quite silent on FM input (used for my iPod)



--JRC


  #13   Report Post  
Posted to rec.audio.tubes
[email protected] vwmicrobus@gmail.com is offline
external usenet poster
 
Posts: 5
Default Restoring a Sherwood S-5000

On Sunday, January 19, 2014 2:07:28 PM UTC-5, hugeshows wrote:
Good god, those voltages are HIGH!


yea, that's what I thought.. I did measure my AC line, but don't remember the exact voltage, but it was not out of the norm.

No tubes were removed, the amp was at idle with about 10 minutes warm-up time.
I'll take a look at the AC HV tonight.

Oh, and I don't suppose there is a line voltage selection of any time is there? If it was tapped for 110VAC that might explain it. I get something close to 120-125 VAC here.

I have a variac, and so I will put it inline and see what it takes to get them lower. I guess I should look at AC filament voltages too?

--John
  #14   Report Post  
Posted to rec.audio.tubes
hugeshows hugeshows is offline
external usenet poster
 
Posts: 29
Default Restoring a Sherwood S-5000

I'm trying to dig up my notes on some of the S-5000s I've done before. I am having a hard time remembering exactly what the volts came up to after re-capping, but I seem to think that your number is quite high.

It is likely that our differences are a result of line voltage, the fact that I've still got old caps in mine, or both. I will do some more measurement soon and see if I can come up with a reason. Our units are pretty close in serial numbers. I can't tell off hand if those repairs in there were done correctly, they look a tad sloppy... But I would expect other problems to arise very quickly at those voltages if something was really wrong in there.

But 470v is a LOT higher than any 7189 is rated for, by about 30v... So yeah, no wonder you arced over some tubes in there. Frankly, I'm a bit surprised the ones you have in there now can handle it.

Anyway, we both have some more measuring to do. I'm curious about your line voltage. Let's start there.. Maybe yours is abnormally high and mine abnormally low...

-forkinthesocket

No tubes were removed, the amp was at idle with about 10 minutes warm-up time.

I'll take a look at the AC HV tonight.



Oh, and I don't suppose there is a line voltage selection of any time is there? If it was tapped for 110VAC that might explain it. I get something close to 120-125 VAC here.



I have a variac, and so I will put it inline and see what it takes to get them lower. I guess I should look at AC filament voltages too?



--John


  #15   Report Post  
Posted to rec.audio.tubes
hugeshows hugeshows is offline
external usenet poster
 
Posts: 29
Default Restoring a Sherwood S-5000

It looks like I may be getting my parts today, if the tracking info is to be believed...

Meanwhile, here is the video I promised showing the LF driver 'sucking in' when high amplitude bass attack happens. I am hoping the rebuilt power supply will solve this issue as it usually does. This whole thing has prompted me to want to really investigate the phase of the output on this amp...

https://www.dropbox.com/sc/fq395aclt88zwyl/tyuwer-T-Z

Might wanna download it, the dropbox player kinda stinks. And please, these are my test speakers. Yes I know the cones are dirty thank you very much..

-forkinthesocket


  #16   Report Post  
Posted to rec.audio.tubes
hugeshows hugeshows is offline
external usenet poster
 
Posts: 29
Default Restoring a Sherwood S-5000

Hello all,


So I did in fact get my parts the other day, and I've made some nice progress. Sadly, one of the caps arrived with some damage, apparently from the factory, and I am in the process of returning it.

However, the large 40/40/20/20 filter capacitor is just fine, and it has now been installed. The results were nothing short of stunning, more on that later. All of the HV+ voltages pretty much stayed the same, actually losing a volt here and there. I suspect that either my line voltage was slightly different or perhaps even that missing volt was ripple that existed with the old cap and was fooling my DMM. Unfortunately, I'll never know because I have yet to buy a new scope since moving cross country. My old one was a TEK 535A, with Scopemobile, so it was a bit big for my current flat. So whether it was ripple or just a line fluctuation, I'll never know but overall the voltages did not change really from what I posted earlier.

The sonic situation got noticeably better immediately on first audition. There was no 'breaking in the cap' or anything like that, something I'm not really convinced of anyway... The first thing I noticed right away was that the bottom two octaves suddenly were really there. They had been there before, and I had gotten fairly used to the sound of the amp as it was. But replacing the main cap made the hum that was barely there to begin with disappear, and all of a sudden there is a quickness and depth to the lower octaves that just wasn't there before. In addition, the mids and highs seem to have really perked up as well, the highs have increased markedly, while the mids just seem clearer. The sound of the amp improved so much it was just obvious within the first 30 seconds of listening. So at least for now we can say that the cap I ordered works well in this amp. Here's how it was installed:

First off, while most of us have recapped a few amps in our day, I strongly recommend doing this the way I did, because I have done this particular amp several times and there are annoying and time consuming mistakes that are easily made and I will show you how to avoid them here. First, snap a picture of the underside of the main cap (C53 in Sherwood Scehmatics, C1 in Sams)

https://www.dropbox.com/s/u8ze7xcu7f...onnections.jpg

So once you have a record of what went where, you are good to start. First of all, you will NEED at least a 140W soldering GUN to get through this. Don't even try this with a pencil iron, there is too much metal down there and it will heat sink your little iron into uselessness. Don't use a butane iron. Those things have exhaust ports that will melt nearby wires, and you'll feel really stupid if you do that. Use a big Weller gun of at least 140W and you'll make it through. Make sure you have some desoldering wick on hand. A sucker will frustrate you on this cap.

Here's the general idea... All of the skinny rubber coated wires should just be snipped right by the terminal. Don't bother trying to desolder these, as the heat needed will make the vinyl jacket melt back even further than if you had just snipped and stripped. All of the resistor leads and cloth transformer wires should be de-soldered and removed intact. The power resistors do not have any extra length on them, so you are forced to desolder their terminals completely and unwrap and extract the leads. Use skinny needle nose pliers for that. Here is what is left after you've snipped all the little wires (except for two grounds underneath the resistor)

https://www.dropbox.com/s/ur200ncddd...53_snipped.jpg

Now you're ready to begin desoldering. Using the solder wick, carefully reclaim the 4.7K resistor, remove the 33 ohm resistor coming from the rectifier, and then all of the cloth covered transformer wires. Use desolder wick to remove as much solder from those old terminals as possible, and then with the pliers, carefully peel the lead off. The factory typically wrapped the lead around the terminal a couple times and you'll be surprised how much you can reclaim. Going slow and desoldering thoroughly is the key. Once you've gotten all those off, you can either desolder or snip the two black grounds underneath the power resistor depending on how much spare slack is available in your amp.

Once you've finished that, all that is left is the ground tab that is soldered to the chassis. Don't even attempt to desolder that. The chassis and can are such good heatsinks, you'll need 250W to do it, and as you are about to see there is utility in doing it another way. Flip the amp over, tilt the capacitor out of the clamp, and simply bend it back and forth until the tab snaps off. Trust me. Set the old cap aside. Now flip the amp over and using larger pliers, grab the tab sticking out of the solder and twist and pull it like a sadistic dentist. If you do it right, you should be left with a blob of solder and a nice clean slot in the chassis. Hmm, thought I had a pic of that but guess not.

Ok, so now you've got the old cap out and everything is just peachy. Time to take a break. Now we need to carefully compare the cap we pulled out to the new one. Here are some pics of that. Remember I told you to trust me and just rip the old cap out? Well here's where it comes in handy... We now have a perfect guide as to the orientation of the cap as it was in the chassis, and that is very critical for both alignment of the connections, but also making sure that the rectifiers first cap is 20uf and no more or less. We must align at least that section of the cap to its original position in the amp. Otherwise, we'll be making jumpers and splices to high voltage connections exposed to heat. That's not ideal.

So here are some pics comparing the caps. Sorry they're not so hot.

https://www.dropbox.com/s/0uhqs4dpen...p_Newcap_1.jpg

https://www.dropbox.com/s/efyhagz1ru...p_Newcap_2.jpg

https://www.dropbox.com/s/raq55pq9jr...p_Newcap_3.jpg

As you can see, other than the shoulder at the base, the dimensions are identical. So here's the important bit, triple check it before moving on: Stand the caps up next to each other as in the third picture. The missing tab is our key that lets us know how the cap was in the chassis in the first place. The 20uf section for the rectifier is the one to the right of the missing tab, where the red wire went. So grab the new can, read the legend on the side, and rotate the cap until the 20uf section in positioned in the same place relative to you, and mark the tab that will be going through the chassis with a sharpie. as in pic #3. Triple check this! You don't want to solder this can into the chassis and be like "oh ****" later on. That's one critical comparison out of the way.

There is one more thing you must check before installation. Look at picture #1 above. Notice anything? The ground tab on this side of the can has no hole! And, if you look at the original can, you see that this position had wires soldered to the tab. So, seeing that, the time to drill a hole is obviously before installation. The correct size in this case was 9/64". With that out of the way, it's time to stuff the cap in... But wait... If you have rust on your amp top that you plan on removing at some point, the time to remove the rust under the cap is NOW, before you stuff in the new one. So grab some scotch-brite and some CLR and you don't have to do the whole thing, but at least to the bits you won't be able to get at later. Here's the cap stuffed in place after cleaning the rust underneath:

https://www.dropbox.com/s/a4svoftuaz...Clean_Rust.jpg

As you can see, it look stock with the exception of the sticker. If you want to remove the sticker for appearance, the time to do it was before you soldered it in!

Rather than trying to remove the blob of solder on the chassis, it's better to just fold the tab over and press it into the blob as far as it will go (cold) and then use your big solder gun to melt more solder into it. This will work, you have enough heat with a gun.

https://www.dropbox.com/s/4sbo4o1lz9...%20%281%29.jpg

There's the new cap installed. As you can see, there was plenty of heat to bury the tab in that solder blob, and it made an excellent connection. So re-soldering the wires is in the reverse order of removal, and it's pretty important to do it that way. First reconnect all the grounds. After the grounds, do the all the red and orange wires but don't solder the skinny red wires, just connect them up. After that, connect the 33 ohm resistor, the two OPT leads, the 4.7K resistor, and solder it up. That terminal has a lot going on, so go carefully if you want it to be neat. After that, connect the 4.7k and the remaining wires and solder them up. The result should look stock like this:

https://www.dropbox.com/s/vi2i11spzl...%20%282%29.jpg

That's all there is to C53! The result as I said before has been night and day and this amp sounds fantastic already, and we've not finished the entire power supply yet.

Now I'd recommend stopping for a bit, coming back, double checking all the connections, and firing it up with the bottom off so you can measure all thje voltages again. Be certain before you turn it on. A good 5AR4 is not cheap to replace.

Now that we've got the old cap out, we can inspect it a bit. Bend back the tabs as I have done he

https://www.dropbox.com/s/1bd9r7wmac...53_removed.jpg

If you look carefully, you'll see that one section in particular has started to ooze the white goo from around its terminal. Interestingly, it's the [email protected] section, the smallest section in the can! Well, this new can now has that same section getting [email protected], so that is not likely to happen again anytime soon.

Okay, so until I either get the replacement cap for that second twistlock or decide to do the bias supply, I'm done for a few days.

Cheers,


-forkinthesocket









  #17   Report Post  
Posted to rec.audio.tubes
hugeshows hugeshows is offline
external usenet poster
 
Posts: 29
Default Restoring a Sherwood S-5000

errata from last post:

1) When orienting the cap as I described, it is not only important to align a 20uf section with the rectifier, it is also important to align the two 40uf sections with their original locations! So, the new cap has two 20uf sections, meaning there are two ways you can orient it and have a 20uf section for the rectifier. One of them will give you the two 40uf sections where you want and one way won't. Starting with the section to the right of the missing ground tab, and going counter-clockwise, orient the new cap so that you start with 20, then 40, and 40, then 20, again starting with the rectifier's section and going counter-clockwise. The other way is 20,20,40,40 and that isn't what you want.

2) I mentioned that the new cap was 500v, but it is actuall 525v as I had said in earlier posts.


-forkinthesocket
  #18   Report Post  
Posted to rec.audio.tubes
[email protected] vwmicrobus@gmail.com is offline
external usenet poster
 
Posts: 5
Default Restoring a Sherwood S-5000

On Wednesday, January 22, 2014 2:32:18 PM UTC-5, hugeshows wrote:
... And please, these are my test speakers. Yes I know the cones are dirty thank you very much. -forkinthesocket


Finally had a chance to get back, it's been quite a week of keeping FM radio working in my area (my current day-job)

You will be pleased to know that I have the same Tannoy speakers as you (but mine are clean!) Funny story as to how I got them, a certain TV station I used to work for got a package deal for a monitoring station, and it included these Tannoy speakers. They would not fit in the space alloted, so I traded them for a set of Optimus bookshelf speakers (the smallest they made) and we were both lived happily ever after...

So my line voltage is 120.6 VAC with the same meter.. I put the amp on a variac and brought the line voltage to 110VAC and got close to the same measurements as you did. Does the primary transformer have voltage taps?? I didn't really look hard.

I hope I am not destroying anything by continuing on such high voltages.. power tubes are disposable, they are not anything special, but I don't want to cook the amp or the preamp tubes.

--JRC
  #19   Report Post  
Posted to rec.audio.tubes
hugeshows hugeshows is offline
external usenet poster
 
Posts: 29
Default Restoring a Sherwood S-5000

Hi There,

So my memory must be failing me in my old age. First off, I've been saying this whole thread that the max capacitance of a 5AR4 is 20uf. Well, I knew better at one point and I am embarrassed to say that I've looked it up and it's 60uf. So, you could put more capacitance at the rectifier, but the result would be raised voltages. I can see that your cap has been replaced.. Can you check and see what the capacitance off that first section is? If not, please measure the AC output of the transformer secondary (the HV feeding the rectifier) and post your findings. It also seems that the big main cap has two sections tied together. Knowing all those values would be useful.

Your line voltage is right where mine is at. Unless we see a difference in the voltage coming off the power transformer, the elevated voltages are probably a result of the work that's been done. I really wonder what that section of the cap is coming off the rectifier.

On the other hand, if those output tubes can handle the voltage and it sounds good, we might want to go with it. The preamp tubes are not getting that much more voltage than they're used to, they're not cooking. Those Russian military versions of the EL84 you have are rated for 500v on the plates, so you're OK there. You'll be forced to keep looking for HV tubes but that thing is probably making 26-27W at those voltages! Have you measured the plate current draw yet? What's the BIAS voltage running at?

So, here's what I need to help:

AC voltage on HV secondary of power trans (loaded)
Capacitance of that first section
Bias voltage and plate current measurements

While those repairs seem a bit klunky, they might be OK. I'm a little worried about whatever splice that is shrinkwrapped near the transformer, though It might just be a ground wire.

We'll get back to the phono section soon, let's check and make sure everything else is ok first.

Cheers,

-forkinthesocket


  #20   Report Post  
Posted to rec.audio.tubes
hugeshows hugeshows is offline
external usenet poster
 
Posts: 29
Default Restoring a Sherwood S-5000

Hello all, and particularly JRC,

I have done a LOT of work on the S-5000 this weekend, and it is going to take quite some time to write all of if up. However, while rebuilding the bias supply, I think I may have stumbled across a reason why JRC has such high plate voltage. After replacing all the caps and diodes in the bias supply, the bias voltage wound up being quite a bit higher than before. As a result, the tubes were biased pretty cold, and were only pulling around 7 watts each. However, during this time I noticed that my plate voltage climbed way up, almost to where JRC was seeing his.

I guess it seems pretty straightforward, drop the plate current and the tubes load down the HV+ less. I've never seen it quite so dramatic as this, but I think it may be a good starting point.

JRC - Can you please do the following and post results?

1) Measure the ACTUAL resistance of your 12 ohm 1W cathode resistors.
2) Measure the voltage drop across them
3) Measure your plate voltage again since we will be using it for math

Calculate your plate dissipation (per pair) of output tubes, and then the wattage. If you're not familiar with those calculations, go here and plug in the numbers:

http://www.webervst.com/tubes1/calcbias.htm

From this we can figure out just how many watts per side you are pulling and your idle current. I have a sneaky suspicion that while your plate voltage is quite high, your dissipation is going to be pretty low. This would explain why your tubes aren't glowing cherry red.

One of the things I did this weekend that I need time to write up is I replaced those 12 ohm cathode resistors with 4 x 10 ohm 1W 1% precision resistors. Now each tube has its own cathode resistor, and because they are 10 ohms each, we can very quickly determine the idle current in each tube rather than each pair, and because it's 10 ohm, no calculator is needed!

More to come.

JRC, please post what you find out. I think we're close here!

Cheers,

-forkinthesocket


  #21   Report Post  
Posted to rec.audio.tubes
hugeshows hugeshows is offline
external usenet poster
 
Posts: 29
Default Restoring a Sherwood S-5000

While I wait for JRC to update us on that, I thought I would post on some progress I've made. I've re-done the bias supply and finished the HV+ filter sections, for starters... But I am too lazy to write that up right now! Let's pause that part of the thing and go over the electrical safety for this amp.

Lots of people think that automatically putting a 3-prong plug on a vintage amp is a good idea. There is partial truth to that. It is certainly a lot more important on a guitar amp than it is a hi-fi amp, however. On a guitar amp, you can be holding an instrument that is at whatever potential the chassis is at, and if you touch a grounded microphone with your mouth it can be enough to rattle your fillings! That is a very potentially dangerous situation, especially considering the wide array of generally decrepit electrical situations one typically finds on a stage. So folks who automatically put a three-prong cord on a guitar amp will find no quarrel with me.

Putting a three-prong outlet on an integrated tube receiver/amp however is a different animal. For starters, chassis ground is signal ground on these amps. If you ground the chassis to your house ground, you have introduced a level of safety perhaps, but you've also put a potentially very noisy and dirty ground on your signal ground. This raises the probability of ground loop related issues, where AC travels your signal ground, and just about guarantees that your phono stage will be a complete pain in the ass to get quiet. Modern amps that are designed to have 3-prong plugs are a different beast, though not immune to this problem either. It's not uncommon to see "ground" floating a few volts above actual ground, and in lots of areas in the US, ground is merely bonded to the neutral bus in the breaker panel. So essentially, you've just connected your amp chassis to neutral - the same neutral that connects to every appliance in your house, and gets dirtied by any number of motors, compressors, dimmers, etc.

I think that converting to 3-prong on a the S-5000 is a mistake and not at all necessary for safety. If somebody feels otherwise, no reasonable argument will be ignored, so speak up. Safety is more important than tone.

Does that mean you should leave the stock power cord on your amp? No. For starters, the original cord is not polarized. Putting a polarized plug on your amp will do more for safety than just about anything else. First off, it guarantees that the hot leg of the AC goes through the fuse and not the neutral leg. That's very important. There's a twin capacitor in the S-5000 located near the convenience outlets. It's a ceramic and not at all likely to fail. But, if it DID fail by shorting, and you just happened to have the un-polarized plug still, then there's a 50/50 chance that the chassis now has full 120AC on the it, and that same 120AC is also bypassing the fuse now too!

On top of that we have the convenience outlets themselves, which while not terribly unsafe, are also unpolarized, but moreover using them tends to dirty the noise floor of the amp. So we need to deal with the electrics. Something has to be brought up to date. Here's what I do:

1) Replace the original cord with a polarized two-prong lamp cord.
2) Disconnect the courtesy outlets and all extra wiring for them
3) Wire the mains cord to bypass all that original extra stuff
4) Replace the dual .002 cap with a .01 cap, and move it behind the power transformer where the center-tap grounds.
5) Move the vintage Sherwood tag to the new cord!
6) CHECK THE VALUE OF THE FUSE!! SOME DIMWIT STUCK A 10A FUSE IN THIS UNIT!!

Here's what the unit looks like gutted of all the unnecessary AC cordage and with a new power cord:

https://www.dropbox.com/s/j6si8yqs91...%20%282%29.jpg


See how nice that cleans up? All of the wires to the receptacles is gone, the chassis noise cap is now behind the power transformer (and is now ALWAYS on neutral!) So by forcing the chassis cap to be on neutral, and the fuse to be on hot, we have improved the safety of this amp significantly without messing with ground or screwing up noise levels. All while maintaining a fairly stock look:

https://www.dropbox.com/s/u5dfec453z...%20%283%29.jpg


So that leaves the question of the AC receptacles... There are a couple choices here. For starters, remember how I mentioned that I've added individual cathode resistors? Well, we now have 4 external terminals unused! These AC receptacles can be re-used as bias current measurement points! If you're fearful about what would happen if somebody plugged a tuner into the socket (not much) you can solve that by stuffing the sockets with cut-off AC prongs, allowing probe insertion, but blocking an actual plug!

If you don't mind altering the chassis, those holes line up perfectly with certain styles of slider switch. You could add any number of options, either with the bias or even put a standby switch if you wanted (not recommended).

In any event, the amp will be safer and possibly less noisy after you do this.

More to come!


-forkinthesocket
  #22   Report Post  
Posted to rec.audio.tubes
hugeshows hugeshows is offline
external usenet poster
 
Posts: 29
Default Restoring a Sherwood S-5000

Hello all,


Well I've recently finished up the electrical portion of my S-5000 restoration. I've learned quite a few things along the way, and even though I've done several of these before, I made a couple mistakes this time that taught me a few things about how this amp operates.

First off, let me cover the mistakes I made in posts previous to this.

Mistake #1

Changing the chassis capacitor in the way I did it was a bad idea. I had a fundamental misunderstanding of the way that capacitor was designed to work in this amp, and it wasn't until I noticed increased hum that I realized my blunder. Simply using a single cap as is so common in radios and other types of amp doesn't pan out well with the S-5000. The reason is that the original cap is actually two caps connected in series and tied in the center to the chassis. One end of these caps are on hot, the other neutral. The result is a cancellation effect. A single cap simply dirties the chassis currents by connecting it to only one leg. One option would be to simply remove the cap for safety, but after thinking long and hard about it I began to ponder whether the cap was there to deal with inductive spikes on the power transformer when switched on or off. Without any way to answer that question, I simply punted and restored the original capacitor back into the circuit. The added hum was gone instantly. I'll write up that whole AC line redo in a little while...

Mistake #2 (JRC, I think this might be your answer to phono hum)

Believing my eyes and the schematic. The bias supply turns out to be a finicky thing on this amp. If you read the schematic, either Sherwood OR Sams, you see that there are three capacitor sections in the supply. In the original amp, these are all in a twistlock can and share a common positive, rather than a common negative like just about every other twistlock can. If you look at the pictures I posted earlier, you see that there are several things tied to the "ground" on this can, but that is incredibly misleading. You see, while this cap has a common positive, it is NOT on the can body!! There is a terminal that has the common positive, and it is NOT connected to the can. Whoever drew the schematics made the same assumption I did, that the common positive is connected to ground. It is not. It is connected only to the center-tap of bias winding, the DC filament return, and the ground bus that for the entire preamp section!! If you follow the schematic or your eyes when you rebuild the bias section, and you connect the common positive to ground, you will be instantly greeted by a NASTY hum as soon as you connect a magnetic phono cartridge! JRC, since your bias supply was rebuilt, and kinda sloppily, you may wish to redo that section and be sure that the common positive is not tied to the chassis!

I got everything dead quiet in this amp until I tried the phono section which was working beautifully before my rebuild. It now had a horrible hum, and so I knew it must have been something I had done. I poured over the amp with a fine-tooth comb, uncovering 3 mistakes from the factory in the process including two joints that were never soldered, one was the center-tap of the AC primary at its chassis junction!! The other was a tone control resistor that was connected but never soldered to the pot. Obviously, this amp had some pretty green hands making it. After hours of frustration, I started measuring things. I compared the bias circuit carefully to my restored version. After finally getting my meter out and measuring the original cap (still in place but disconnected) I discovered the truth! The schematics are wrong and that circuit connects to the center tap of the bias secondary ONLY, and is floated from the chassis. One wire snipped out and voila! A dead quiet phono pre!


I've got a lot more pictures to take and upload, and I'll probably get to that tomorrow. But I wanted to go ahead and correct my mistakes for the record now, lest anyone else go down my erroneous path with the bias and AC supplies.


Cheers,

-forkinthesocket







  #23   Report Post  
Posted to rec.audio.tubes
hugeshows hugeshows is offline
external usenet poster
 
Posts: 29
Default Restoring a Sherwood S-5000

Hello all,


So I am finally getting around to writing up the place where I decided to call it quits, electrically speaking. Generally, I find the coupling caps to be good in the S-5000, and so when there are no indications of problems, I leave them alone. I think to do otherwise changes the character of the amp, and that is not something that I either encourage or discourage, because it's a personal choice. However, I think that for my tastes, once the power supply is up to snuff and everything checks out electrically and the amp sounds good, that's when I usually stop.

First off, the power supply rebuild... As you know, I went with the reproduction twistlocks from CE, which I purchased from AES. These capacitors seem to be of high quality, though I did have issues with the 1" diameter can and had to get a replacement. Regrettably, even the second one was a bit out of round at the base as if the crimping machine were having issues with that size, or the die was out of round. Anyway, I decided to install it and it worked out fine. There was nothing remarkable about this cap except that it was a 20/20 cap and the stock was a 30/20. So I added a 10uf cap in parallel to the underside and wound up with over 35uf measured for that section.

The bias supply is what turned out to be the most challenging, since it is sort of an odd circuit, the way its positive side is floated from the chassis. The main issue is that I decided to rebuild the voltage dropping resistors using the stock parts and obviously values as well. The result of this is that the increased voltage from the silicon diodes in the bias circuit along with resistor values that were derived for a selenium rectifier caused an elevated bias voltage which made the output tubes run rather cold. Keep in mind that the bias adjustment pots on this amplifier merely adjust the balance of bias voltage on each channel, they do not control overall voltage and there is no way to match each tube's current draw across channels.

After rebuilding the circuit with the stock resistors and new capacitors (underneath) I started taking measurements. I was seeing that the output tubes were drawing less than 15ma plate current at idle, and that's cold for any 7189 amp even at 440v plate. Bias voltage was in the 24v range, and the DC filament supply for the phono section was at about 26.5. Clearly, the stock circuit could not supply the right voltages with a silicon rectifier. Rather than attempting to re-engineer the bias and DC filament circuits just now, I decided to experiment with putting different value resistors in series between the diodes and the first capacitor, and I arrived with an interesting solution.

https://www.dropbox.com/s/gzmtpckjoy...ias_Supply.jpg

Keep in mind that those two green ground connections were later deleted in regards to the mistakes I mentioned in my last post. Anyway, as you can see, I've taken a very old Ohmite 10w wirewound resistor of the screw-mount type and mounted it inside the chassis, bypassed by a 40 ohm 2w precision resistor that Stephie sent me many years back. The resulting parallel resistance is 8 ohms, and that turns out to put the voltages right where I want them.

Why chose two resistors instead of one? Well, I wanted to be able to adjust the bias voltage a bit. I found that 10 ohms ran it just about as hot as I'd ever want the tubes to run, around 24ma a piece with some tubes! 8 ohms got my used Amperex 7189s to run at 21ma a piece, which is about where these Sherwoods run stock. Yes, that's a LOT for this type of tube, which is why you have to stick with ones that can handle the higher plate voltage. Anyway, the 40 ohm resistor can be removed by me at any point if I want to run things a but hotter, or have tubes that need a little less bias to get their current up. If I find a 2w rheostat to replace it with that I can mount internally without drilling, then I might use that as the shunt. Basically, by using a big overrated resistor like that 10w, I guarantee that my bias voltage won't fail due to a crappy pot. If I put a rheostat where that 40 ohm resistor is now and it faults open, the bias circuit fails hot, but safe because the 10 ohm resistor is in parallel.

So, with this arrangement I wind up with 23.6 volts at the top of the DC filament supply, and around 19v bias finally making it to the tubes after the balance pots. This gives me around 19-21 ma idle current per tube at 440v plate.

So, I've also modified that cathode resistors, and done something new - I reused the AC accessory sockets for bias measurement points, and it works brilliantly! You can either measure each tube individually, or measure the balance of a pair by connecting the meter to both points. Since the S-5000 is setup with a balance type bias circuit, this works out great and can be used in place of or along with the hum balance test described in the manual.. FYI- Hum balance in the S-5000 is not the classic hum balance circuit you find in other amps, it's really a fixed bias balance adjustment using injected and then cancelled hum to determine the center point.

So the bias has been left stock, except there is now 8 ohms between the diodes and the rest of the circuit. The dual 12 ohm 1w cathode resistors have now been replaced with 4 individual 1w precision 10 ohm resistors. From the cathodes, I ran a 4 conductor solid core ribbon wire over to the AC sockets which were reclaimed in the AC supply rebuild (more on that later). Here's how I did it:

https://www.dropbox.com/s/o20s9dxgon...sistor_Mod.jpg

The ribbon cable simply goes down between the output tubes, where it ties to each cathode. From there, it runs under the lip of the chassis towards the sockets. Just before the sockets, there's a screw hole. At that spot, I carefully bent a dip in the cable (solid core) and wrapped it with a bit of friction tape to protect it from future screws. And then each channel's pair was soldered to a socket, I laid it out logically.

Now I can measure each tube's bias, correlate "hum balance" to real-world figures, and see just how hot I'm running things without even opening the chassis. If you measure from each terminal to chassis, you see a number which is converted into ma with no math at all, save moving a decimal twice.

https://www.dropbox.com/s/jic4damuuo..._terminals.jpg

Here is the AC power input and the bias measurement points again. This is after I restored the stock chassis-line capacitor arrangement, but now that I had re-purposed the AC receptacles that the cap was mounted to, I had to add a terminal strip to the bolt on the transformer. From there, I re-wired the power supply to put the hot leg of the AC through first the fuse, then the power switch, then the transformer primary. Jumpers were made to connect hot to the new terminal strip and the cap, where neutral and the other primary leg was connected. The cap was grounded to the chassis at that spot, which seems to have the same hum level as its old position so far, fairly low.

I must say that I find having bias measuring points far more useful than an accessory outlet that dirties the noise floor when used, and despite a nostalgia for keeping things stock, this modification works well for me.

I'm getting sleepy, so that's all for now.


Cheers,

-forkinthesocket
  #24   Report Post  
Posted to rec.audio.tubes
[email protected] paintedfinishes1@gmail.com is offline
external usenet poster
 
Posts: 1
Default Restoring a Sherwood S-5000

I have an opportunity to buy an S 5000 in beautiful shape. Would you be kind enough to call me to discuss restoring it.
Bill
630 745 8261
  #25   Report Post  
Posted to rec.audio.tubes
[email protected] cgoroo@gmail.com is offline
external usenet poster
 
Posts: 1
Default Restoring a Sherwood S-5000

"C24/B - 250v 204v"

Hi, did you figure out why you measured 46v below what the schematic reads?

Sorry if I missed the explanation but I only see how you resolved the bias voltage supply.

Cheers!


  #26   Report Post  
Posted to rec.audio.tubes
hugeshows hugeshows is offline
external usenet poster
 
Posts: 29
Default Restoring a Sherwood S-5000

On Wednesday, July 23, 2014 11:49:00 PM UTC-4, wrote:
"C24/B - 250v 204v"



Hi, did you figure out why you measured 46v below what the schematic reads?



Sorry if I missed the explanation but I only see how you resolved the bias voltage supply.



Cheers!


Sorry folks, haven't checked in here in a while. I'll take another look this weekend and see if I can answer some of these questions.

Cheers!
  #27   Report Post  
Posted to rec.audio.tubes
Peter Wieck Peter Wieck is offline
external usenet poster
 
Posts: 2,418
Default Restoring a Sherwood S-5000

On Sunday, January 12, 2014 5:11:25 PM UTC-5, hugeshows wrote:
Ok, pics coming soon...



First step was to take voltage measurements off the bias and HV+ rails. Here's what I got on my S-5000. By the way, there are two variants of the S-5000 that I will discuss later, basically the older, longer version and the newer, shorter version. The one I am working on here is one of the shorter types.

A few things out in the deep background he

a) Voltages at the wallplate: These days, with average household electrical use being anywhere between 50% and 200% greater than it was when that Sherwood was 'new', Utilities that have not significantly upgraded their final distribution systems (most) have increased the voltage in those systems. It is not uncommon for us to see up to 130V commonly at the wallplate at our house these days. And 5% over the 'nominal' 120V would account for most of your B+ variations.

Do you have access to a variac such that you might reduce the input voltage to 115V or so (much closer to what would have been the case in the 1960s throughout most of the US)?

b) Selenium diodes decay over time (and when they fail it can be quite spectacular and leave you gasping in amazement). As they decay their resistance increases.

My guess is that your selenium diodes are 'out' about 10% - so the higher line voltage overcomes some of that. NOTE and WARNING: if I am correct in that assumption, those diodes are closing in on the failure point. Get that block (or individual units) replaced ASAP.

I am not above installing the occasional dropping resistor in some of my equipment that was designed against a typical wallplate voltage of 110V or so - most 'stuff' made in the 1930s and 1940s. Post WW-II, nominal was about 115V, into the 1980s, mostly around 120V. And from about 2000, commonly well over that voltage. Filaments do not like voltage in excess of their rating. 5% high typically will translate to a 40% drop in life. AND, despite anecdotal and cult beliefs to the contrary, nor do they like low voltage very much either. Look up 'lazy cathode' and other phenomenon along those lines. Generally, there is nothing much wrong with 5% low. Beyond that and the consequences are worse than the benefits. Interesting aside - clearing 'lazy cathode' (AKA 'rejuvenation' in some circles) involves running filaments at a high voltage under controlled conditions. So be aware.

c) Drifted resistors - resistor technology has changed (mostly for the better) since the 1960s. These days, even 'cheap' resistors are typically well within 5% however they are marked. But older compositions often drifted - usually higher. It is always a good idea to check all the resistors.

Best of luck with this - it is a worthwhile endeavor.

Hum in the pre-amp: Given the extra amplification of the phono-stage, it will exaggerate any hum in the system that may not show up at from the line-level inputs. But, as it happens, most sources of hum in the phono section will be related to bad shielding, and/or a shield that is grounded at both ends (or the one end that should be connected is not). Start with the simple stuff such as physical damage or a failed connection. Then, look for the obvious - caps.

Never mind Andre - he is neither of consequence nor any particular use. Note also that the pictures (of himself) he allows are over 30 years old... There is far more ego than substance going on there.

Peter Wieck
Melrose Park, PA
  #28   Report Post  
Posted to rec.audio.tubes
[email protected] jurb6006@gmail.com is offline
external usenet poster
 
Posts: 2
Default Restoring a Sherwood S-5000

I notice things have died down a bit.

Anyway, I looked and foud that the S-5000 used the Williaamsin configuration but the S-5000A did not. I had an S-5000A for a while. Damn thing got disconnected from one speaker at some point and had an arced over tube socket. Not happy.

But you got the real McCoy I guess.

So, do anything lately on it ?
  #29   Report Post  
Posted to rec.audio.tubes
hugeshows hugeshows is offline
external usenet poster
 
Posts: 29
Default Restoring a Sherwood S-5000

On Sunday, October 26, 2014 5:49:24 PM UTC-4, wrote:
I notice things have died down a bit.

Anyway, I looked and foud that the S-5000 used the Williaamsin configuration but the S-5000A did not. I had an S-5000A for a while. Damn thing got disconnected from one speaker at some point and had an arced over tube socket. Not happy.

But you got the real McCoy I guess.

So, do anything lately on it ?


A bit, actually. Of late I've been on audioasylum more than here, but I certainly don't mind coming to some sort of conclusion with this thread, and I realize there is more work to do. I recently acquired an S-360, a rare monoblock Sherwood meant to turn the S-4400 unit into a complete stereo amp/preamp, and I will be diving into that soon.

Are there any particular questions still outstanding that you had?


Cheers.
  #30   Report Post  
Posted to rec.audio.tubes
[email protected] jurb6006@gmail.com is offline
external usenet poster
 
Posts: 2
Default Restoring a Sherwood S-5000

It's really just curiousity.


  #31   Report Post  
Posted to rec.audio.tubes
[email protected] smartbargain@sbcglobal.net is offline
external usenet poster
 
Posts: 1
Default Restoring a Sherwood S-5000

On Friday, October 10, 2014 at 3:02:00 PM UTC-5, hugeshows wrote:
On Wednesday, July 23, 2014 11:49:00 PM UTC-4, wrote:
"C24/B - 250v 204v"



Hi, did you figure out why you measured 46v below what the schematic reads?



Sorry if I missed the explanation but I only see how you resolved the bias voltage supply.



Cheers!


Sorry folks, haven't checked in here in a while. I'll take another look this weekend and see if I can answer some of these questions.

Cheers!



Hello. This is a great write up on the 5000. I just picked up one of these on Eaby. Its the S-5000 20 + 20 Stereo Amplifier. Its the unit that has the 4 pushbuttons on the left front panel for phone manipulation. The tube compliments are 5 Sovtek 12AX7(1208), 2 RCA 7199, I cant make out what the output tubes are as the ink has been worn off but what is left of the lettering is 6BQ5 and 065-090 and the word organ. I would like to know if I should replace the phone tubes(the two at the far left) with something else, I primarily listen to the phone input. Also would I benefit from different 7199's or output tubes. Much thanks for your advise.
  #32   Report Post  
Posted to rec.audio.tubes
[email protected] emailpastorbrian@gmail.com is offline
external usenet poster
 
Posts: 1
Default Restoring a Sherwood S-5000

Just wondering if these can be used as preamplifiers? Do they have a preamp out? Specifically the s5000ii. Thanks
  #33   Report Post  
Posted to rec.audio.tubes
[email protected] ad4kruit@msn.com is offline
external usenet poster
 
Posts: 3
Default PWR transformer for a Sherwood S-5000

On Sunday, January 12, 2014 at 1:52:54 PM UTC-6, hugeshows wrote:
Hello all,

One of my favorite tube amps has to be the Sherwood S-5000. It's a little gem of an integrated amp that is quite easily underestimated. Most people would put it in the same class as a Scott 299, also a 6BQ5 amp, although the Sherwood is really a 7189 amp, and actually uses the higher plate voltage possible with the 7189. It also has larger output transformers, and manages to put out 24w RMS per channel.

The pre-amp section, despite having dated ideas about tone control and Fletcher-Munson curves (thankfully switchable) maintains a very neutral and open sound. The bass and treble knobs are actually usable and helpful at times, and don't have some insane Q that belies their center frequency. The phono section is startlingly good so long as the original Telefunken 12AX7s are occupying the two sockets in the phono section. There are a handful of other tubes that can work there as well, but filament hum and microphonics plague any U.S. made 12AX7 or 7025 I have ever tried in this amp, shield or no.

The use of 7199 tubes as the phase splitter/driver tubes is somewhat unfortunate since they are hard to obtain these days. The upshot is that they seem to last a very long time in this circuit, and they sound quite good. Some have attempted to use 6GH8A in this position, or modern Russian 7199 that are actually re-pinned 6GH8A, and I would strongly discourage that. They don't sound right at all. Just ask the ST-70 crowd. You'd have to modify the circuit, and I think that in this case, that's just daft. The 7199 last too long and sound too good to make that a useful mod, IMHO.

In this thread, I will be going over the basic steps of reviving a Sherwood S-5000 as I rebuild yet another one of these beauties. This is more or less your standard re-cap job, plus replacing the selenium rectifier in the bias supply. There are however some things that are specific to this amp, little tricks for dealing with the tight chassis space, and other stuff too. The way capacitors are mounted in this amp is a real pain. It uses twist-lock can caps, one of which is mounted at a 35 degree angle.

If -YOU- have an S-5000 or S-4400 and you have any questions about it, please feel free to ask away and I will cover the topic in this thread. I've dealt with just about everything there is do deal with on these amps, as this will be the 6th one I've restored. The S-5000II is a totally different beast using 7591s, and I will not be covering that amp here.

Still trying to figure out where I will post pics and schematics so I can post links here, so give me a little while on that.

For those of you exclusively into DIY, the S-5000 circuit is a very cool and sweet sounding 7189 amp. It's the only amp I've seen that gets 24 watts out of a pair of 7189s. I've made one using the Triode Electronics ST-70 board as a front-end and the result was so good that it sold for $1000 despite being a prototype and not terribly well built. It was in a Hammond box as I recall, but I did engine turn the top at least. So we can also discuss DIY around this circuit in this thread if anyone wants.

This is my favorite vintage amp of all time, so I can talk about it endlessly without getting bored.

Feel free to ask away as I prepare some pics and schematics to get this started.


-forkinthesocket


New guy. Desperate for help.
The post about restoring the Sherwood S-5000 caught my eye.
I sure would like to do that, but....
My poor amp has a blown power transformer.
Any ideas on a replacement?
  #34   Report Post  
Posted to rec.audio.tubes
Peter Wieck Peter Wieck is offline
external usenet poster
 
Posts: 2,418
Default PWR transformer for a Sherwood S-5000

On Sunday, August 2, 2015 at 2:33:49 PM UTC-4, wrote:

New guy. Desperate for help.
The post about restoring the Sherwood S-5000 caught my eye.
I sure would like to do that, but....
My poor amp has a blown power transformer.
Any ideas on a replacement?


It would be helpful to know the make/model/condition of your amp. And what specific part of the PT that is blown, if known. For instance, if the primary winding is bad, then it is pretty much hopeless, as with the B+ winding(s). But if it is a filament winding (6.3V or 5V) you may be able to install a separate filament transformer.

If you have any of several Dynaco products, OEM replacements are still being made, less so for other brands, but still out there.

And, of course, are the usual transformer builders such as Hammond and others that have both a range of replacement transformers and will even make one for you at a reasonable price, especially if it is already templated.

Lastly, there are transformer rewinders out there that do a fairly credible job with units that may not be otherwise available. Just look up "Transformer Rewinding Service" and take your pick.

Best of luck with it.

Peter Wieck
Melrose Park, PA
  #35   Report Post  
Posted to rec.audio.tubes
[email protected] ad4kruit@msn.com is offline
external usenet poster
 
Posts: 3
Default Restoring a Sherwood S-5000

On Sunday, January 12, 2014 at 1:52:54 PM UTC-6, hugeshows wrote:
Hello all,

One of my favorite tube amps has to be the Sherwood S-5000. It's a little gem of an integrated amp that is quite easily underestimated. Most people would put it in the same class as a Scott 299, also a 6BQ5 amp, although the Sherwood is really a 7189 amp, and actually uses the higher plate voltage possible with the 7189. It also has larger output transformers, and manages to put out 24w RMS per channel.

The pre-amp section, despite having dated ideas about tone control and Fletcher-Munson curves (thankfully switchable) maintains a very neutral and open sound. The bass and treble knobs are actually usable and helpful at times, and don't have some insane Q that belies their center frequency. The phono section is startlingly good so long as the original Telefunken 12AX7s are occupying the two sockets in the phono section. There are a handful of other tubes that can work there as well, but filament hum and microphonics plague any U.S. made 12AX7 or 7025 I have ever tried in this amp, shield or no.

The use of 7199 tubes as the phase splitter/driver tubes is somewhat unfortunate since they are hard to obtain these days. The upshot is that they seem to last a very long time in this circuit, and they sound quite good. Some have attempted to use 6GH8A in this position, or modern Russian 7199 that are actually re-pinned 6GH8A, and I would strongly discourage that. They don't sound right at all. Just ask the ST-70 crowd. You'd have to modify the circuit, and I think that in this case, that's just daft. The 7199 last too long and sound too good to make that a useful mod, IMHO.

In this thread, I will be going over the basic steps of reviving a Sherwood S-5000 as I rebuild yet another one of these beauties. This is more or less your standard re-cap job, plus replacing the selenium rectifier in the bias supply. There are however some things that are specific to this amp, little tricks for dealing with the tight chassis space, and other stuff too. The way capacitors are mounted in this amp is a real pain. It uses twist-lock can caps, one of which is mounted at a 35 degree angle.

If -YOU- have an S-5000 or S-4400 and you have any questions about it, please feel free to ask away and I will cover the topic in this thread. I've dealt with just about everything there is do deal with on these amps, as this will be the 6th one I've restored. The S-5000II is a totally different beast using 7591s, and I will not be covering that amp here.

Still trying to figure out where I will post pics and schematics so I can post links here, so give me a little while on that.

For those of you exclusively into DIY, the S-5000 circuit is a very cool and sweet sounding 7189 amp. It's the only amp I've seen that gets 24 watts out of a pair of 7189s. I've made one using the Triode Electronics ST-70 board as a front-end and the result was so good that it sold for $1000 despite being a prototype and not terribly well built. It was in a Hammond box as I recall, but I did engine turn the top at least. So we can also discuss DIY around this circuit in this thread if anyone wants.

This is my favorite vintage amp of all time, so I can talk about it endlessly without getting bored.

Feel free to ask away as I prepare some pics and schematics to get this started.


-forkinthesocket


Yea, I did miss a few details, I guess. I wanted to see if I could work the system before I dove in.
I had read several posts about how good the Sherwood S-5000 is so I bought my own. Nice cosmetic condition but a blown PWR transformer. Primary side..

Main problem with getting a non-stock replacement is the tight fit and the 30VDC filament and bias voltage needed.
The numbers on the transformer are B922J3-5 and A949005.
If I can't find an original replacement, I will have to look at the rewinding option. Seem that would be a bit costly. I'm in no hurry, so I will wait a while.


  #36   Report Post  
Posted to rec.audio.tubes
MarkS[_3_] MarkS[_3_] is offline
external usenet poster
 
Posts: 4
Default Restoring a Sherwood S-5000

On Wednesday, August 5, 2015 at 5:26:31 PM UTC-4, wrote:
On Sunday, January 12, 2014 at 1:52:54 PM UTC-6, hugeshows wrote:
Hello all,

One of my favorite tube amps has to be the Sherwood S-5000. It's a little gem of an integrated amp that is quite easily underestimated. Most people would put it in the same class as a Scott 299, also a 6BQ5 amp, although the Sherwood is really a 7189 amp, and actually uses the higher plate voltage possible with the 7189. It also has larger output transformers, and manages to put out 24w RMS per channel.

The pre-amp section, despite having dated ideas about tone control and Fletcher-Munson curves (thankfully switchable) maintains a very neutral and open sound. The bass and treble knobs are actually usable and helpful at times, and don't have some insane Q that belies their center frequency. The phono section is startlingly good so long as the original Telefunken 12AX7s are occupying the two sockets in the phono section. There are a handful of other tubes that can work there as well, but filament hum and microphonics plague any U.S. made 12AX7 or 7025 I have ever tried in this amp, shield or no.

The use of 7199 tubes as the phase splitter/driver tubes is somewhat unfortunate since they are hard to obtain these days. The upshot is that they seem to last a very long time in this circuit, and they sound quite good. Some have attempted to use 6GH8A in this position, or modern Russian 7199 that are actually re-pinned 6GH8A, and I would strongly discourage that. They don't sound right at all. Just ask the ST-70 crowd. You'd have to modify the circuit, and I think that in this case, that's just daft. The 7199 last too long and sound too good to make that a useful mod, IMHO.

In this thread, I will be going over the basic steps of reviving a Sherwood S-5000 as I rebuild yet another one of these beauties. This is more or less your standard re-cap job, plus replacing the selenium rectifier in the bias supply. There are however some things that are specific to this amp, little tricks for dealing with the tight chassis space, and other stuff too. The way capacitors are mounted in this amp is a real pain. It uses twist-lock can caps, one of which is mounted at a 35 degree angle.

If -YOU- have an S-5000 or S-4400 and you have any questions about it, please feel free to ask away and I will cover the topic in this thread. I've dealt with just about everything there is do deal with on these amps, as this will be the 6th one I've restored. The S-5000II is a totally different beast using 7591s, and I will not be covering that amp here.

Still trying to figure out where I will post pics and schematics so I can post links here, so give me a little while on that.

For those of you exclusively into DIY, the S-5000 circuit is a very cool and sweet sounding 7189 amp. It's the only amp I've seen that gets 24 watts out of a pair of 7189s. I've made one using the Triode Electronics ST-70 board as a front-end and the result was so good that it sold for $1000 despite being a prototype and not terribly well built. It was in a Hammond box as I recall, but I did engine turn the top at least. So we can also discuss DIY around this circuit in this thread if anyone wants.

This is my favorite vintage amp of all time, so I can talk about it endlessly without getting bored.

Feel free to ask away as I prepare some pics and schematics to get this started.


-forkinthesocket


Yea, I did miss a few details, I guess. I wanted to see if I could work the system before I dove in.
I had read several posts about how good the Sherwood S-5000 is so I bought my own. Nice cosmetic condition but a blown PWR transformer. Primary side.

Main problem with getting a non-stock replacement is the tight fit and the 30VDC filament and bias voltage needed.
The numbers on the transformer are B922J3-5 and A949005.
If I can't find an original replacement, I will have to look at the rewinding option. Seem that would be a bit costly. I'm in no hurry, so I will wait a while.


You can check out these guys-

http://www.heyboertransformers.com/tubeamps.shtml

They made a custom power transformer for my LK72 Scott several years ago at a very reasonable price. They may know what specs you need already or you'll have to draw up a spec.

BR's,

Mark
  #37   Report Post  
Posted to rec.audio.tubes
[email protected] ad4kruit@msn.com is offline
external usenet poster
 
Posts: 3
Default Restoring a Sherwood S-5000

On Sunday, January 12, 2014 at 1:52:54 PM UTC-6, hugeshows wrote:
Hello all,

One of my favorite tube amps has to be the Sherwood S-5000. It's a little gem of an integrated amp that is quite easily underestimated. Most people would put it in the same class as a Scott 299, also a 6BQ5 amp, although the Sherwood is really a 7189 amp, and actually uses the higher plate voltage possible with the 7189. It also has larger output transformers, and manages to put out 24w RMS per channel.

The pre-amp section, despite having dated ideas about tone control and Fletcher-Munson curves (thankfully switchable) maintains a very neutral and open sound. The bass and treble knobs are actually usable and helpful at times, and don't have some insane Q that belies their center frequency. The phono section is startlingly good so long as the original Telefunken 12AX7s are occupying the two sockets in the phono section. There are a handful of other tubes that can work there as well, but filament hum and microphonics plague any U.S. made 12AX7 or 7025 I have ever tried in this amp, shield or no.

The use of 7199 tubes as the phase splitter/driver tubes is somewhat unfortunate since they are hard to obtain these days. The upshot is that they seem to last a very long time in this circuit, and they sound quite good. Some have attempted to use 6GH8A in this position, or modern Russian 7199 that are actually re-pinned 6GH8A, and I would strongly discourage that. They don't sound right at all. Just ask the ST-70 crowd. You'd have to modify the circuit, and I think that in this case, that's just daft. The 7199 last too long and sound too good to make that a useful mod, IMHO.

In this thread, I will be going over the basic steps of reviving a Sherwood S-5000 as I rebuild yet another one of these beauties. This is more or less your standard re-cap job, plus replacing the selenium rectifier in the bias supply. There are however some things that are specific to this amp, little tricks for dealing with the tight chassis space, and other stuff too. The way capacitors are mounted in this amp is a real pain. It uses twist-lock can caps, one of which is mounted at a 35 degree angle.

If -YOU- have an S-5000 or S-4400 and you have any questions about it, please feel free to ask away and I will cover the topic in this thread. I've dealt with just about everything there is do deal with on these amps, as this will be the 6th one I've restored. The S-5000II is a totally different beast using 7591s, and I will not be covering that amp here.

Still trying to figure out where I will post pics and schematics so I can post links here, so give me a little while on that.

For those of you exclusively into DIY, the S-5000 circuit is a very cool and sweet sounding 7189 amp. It's the only amp I've seen that gets 24 watts out of a pair of 7189s. I've made one using the Triode Electronics ST-70 board as a front-end and the result was so good that it sold for $1000 despite being a prototype and not terribly well built. It was in a Hammond box as I recall, but I did engine turn the top at least. So we can also discuss DIY around this circuit in this thread if anyone wants.

This is my favorite vintage amp of all time, so I can talk about it endlessly without getting bored.

Feel free to ask away as I prepare some pics and schematics to get this started.


-forkinthesocket


I just checked. It would be $120 plus shipping? Not too bad.
  #38   Report Post  
Posted to rec.audio.tubes
[email protected] clittle@kumc.edu is offline
external usenet poster
 
Posts: 2
Default Restoring a Sherwood S-5000

Dear All,

I am seeking practical advice, further I am not a knowledgeable electronics guy, tube or otherwise -- to say the least.

A few years ago I was fortunate enough to find and purchase a Sherwood S5000 II; I am into 50s cars and hot rods and just wanted the aesthetics and joy of tube hi-fi ownership. A Sherwood expert here in the KC area completely refurbished the unit with no shortcuts taken. He only charged me for parts, not labor. Until recently my 5000S has provided excellent service for about two years of moderate use.

A couple of months ago the amp began generating some sort of signal spike that resulted in conspicuously loud crackling noise through the speakers. Since I do not use the amp's metal dust cover I was able to observe bright light flashes emitting from one of the four identical "power" (??) vacuum tubes situated at the rear of the amp.

I pulled out the offending vacuum tube, which unlike its counterparts showed discoloration at the "top" of the glass, presumably plasma vapor deposited metal.

The tubes, I now know, are Russian built electro-harmonic 7591A units. I was unable to contact the fellow who refurbished the S5000 II, so I went online and found multiple vendors for the Russian 7591A tubes. I bought a "set" of four, which I received and which appear identical to the my "original" electro-harmonic tubes.

Now my reason for this query: The cross-sectional diameter of the electro-harmonic 7591A units are too large to fit properly in the Sherwood sockets. What gives?

A brief search online suggests to this novice that these modern aftermarket tubes are (duh) fatter than the original electron tubes. I see mention of aftermarket pin adapters so that tubes with similar electronic properties, but different pin patterns, can be substituted. Does such an adapter exist for my Sherwood sockets?

Alternatively, because the shape of the electro-harmonic 7591A glass housings are slightly tapered cones (thinner toward the top) if one had a half-inch tall adapter 7591-to-7591 the Russian tubes would then fit without side-to-side glass contact, assuming I alternated adapters at every other socket position. Does such an adapter exist?

As it stands right now the four "new" tubes contact their respective neighbor, with the outermost (2) tubes unable to fit squarely into their socket. Am I correct in thinking that such glass-to-glass contact is not good for electron tube lifetime? This mechanical interference has to be putting stress on the glass, right? Should I pay big bucks for NOS tubes that fit properly?

Any advise or suggestions will be sincerely appreciated. I guess it's not the end of the world if I have to replace tubes often, but the present arrangement seems pretty lame to me.

Thanks,

Charlie
  #39   Report Post  
Posted to rec.audio.tubes
MarkS[_3_] MarkS[_3_] is offline
external usenet poster
 
Posts: 4
Default Restoring a Sherwood S-5000

On Sunday, September 6, 2015 at 3:00:42 PM UTC-4, wrote:
Dear All,

I am seeking practical advice, further I am not a knowledgeable electronics guy, tube or otherwise -- to say the least.

A few years ago I was fortunate enough to find and purchase a Sherwood S5000 II; I am into 50s cars and hot rods and just wanted the aesthetics and joy of tube hi-fi ownership. A Sherwood expert here in the KC area completely refurbished the unit with no shortcuts taken. He only charged me for parts, not labor. Until recently my 5000S has provided excellent service for about two years of moderate use.

A couple of months ago the amp began generating some sort of signal spike that resulted in conspicuously loud crackling noise through the speakers. Since I do not use the amp's metal dust cover I was able to observe bright light flashes emitting from one of the four identical "power" (??) vacuum tubes situated at the rear of the amp.

I pulled out the offending vacuum tube, which unlike its counterparts showed discoloration at the "top" of the glass, presumably plasma vapor deposited metal.

The tubes, I now know, are Russian built electro-harmonic 7591A units. I was unable to contact the fellow who refurbished the S5000 II, so I went online and found multiple vendors for the Russian 7591A tubes. I bought a "set" of four, which I received and which appear identical to the my "original" electro-harmonic tubes.

Now my reason for this query: The cross-sectional diameter of the electro-harmonic 7591A units are too large to fit properly in the Sherwood sockets.. What gives?

A brief search online suggests to this novice that these modern aftermarket tubes are (duh) fatter than the original electron tubes. I see mention of aftermarket pin adapters so that tubes with similar electronic properties, but different pin patterns, can be substituted. Does such an adapter exist for my Sherwood sockets?

Alternatively, because the shape of the electro-harmonic 7591A glass housings are slightly tapered cones (thinner toward the top) if one had a half-inch tall adapter 7591-to-7591 the Russian tubes would then fit without side-to-side glass contact, assuming I alternated adapters at every other socket position. Does such an adapter exist?

As it stands right now the four "new" tubes contact their respective neighbor, with the outermost (2) tubes unable to fit squarely into their socket.. Am I correct in thinking that such glass-to-glass contact is not good for electron tube lifetime? This mechanical interference has to be putting stress on the glass, right? Should I pay big bucks for NOS tubes that fit properly?

Any advise or suggestions will be sincerely appreciated. I guess it's not the end of the world if I have to replace tubes often, but the present arrangement seems pretty lame to me.

Thanks,

Charlie


Hi Charlie,

Glass to glass contact is not great idea. Beyond NOS 7591A's, there are other options. Right up front, I do not have any personal experience with the new production 7591A's, just NOS- but these days, that can be a crap shoot as well. Anyway, JJ makes a 7591A that is the same diameter as NOS so they should fit better. Also, the same company that makes the Electro Harmonix 7591A's (New Sensor) also released a so called "re-issue" Tung Sol 7591A. I believe these are the same diameter as the JJ / NOS but appear to be 2x the price of JJ's. If I were going to new production, I would probably go with the Tung Sols.
The spacer idea is neat but you may have to make those yourself. Use a tube socket and tube base. There was a time when the 6GM5 was an NOS 7591A alternative but had a different base so an adapter was needed. The price of a 6GM5 is up there now an NOS 7591A anyway so the climb might not be worth the view.

BR's,

Mark
  #40   Report Post  
Posted to rec.audio.tubes
[email protected] clittle@kumc.edu is offline
external usenet poster
 
Posts: 2
Default Restoring a Sherwood S-5000

On Monday, September 7, 2015 at 7:45:24 AM UTC-5, MarkS wrote:
On Sunday, September 6, 2015 at 3:00:42 PM UTC-4, wrote:
Dear All,

I am seeking practical advice, further I am not a knowledgeable electronics guy, tube or otherwise -- to say the least.

A few years ago I was fortunate enough to find and purchase a Sherwood S5000 II; I am into 50s cars and hot rods and just wanted the aesthetics and joy of tube hi-fi ownership. A Sherwood expert here in the KC area completely refurbished the unit with no shortcuts taken. He only charged me for parts, not labor. Until recently my 5000S has provided excellent service for about two years of moderate use.

A couple of months ago the amp began generating some sort of signal spike that resulted in conspicuously loud crackling noise through the speakers.. Since I do not use the amp's metal dust cover I was able to observe bright light flashes emitting from one of the four identical "power" (??) vacuum tubes situated at the rear of the amp.

I pulled out the offending vacuum tube, which unlike its counterparts showed discoloration at the "top" of the glass, presumably plasma vapor deposited metal.

The tubes, I now know, are Russian built electro-harmonic 7591A units. I was unable to contact the fellow who refurbished the S5000 II, so I went online and found multiple vendors for the Russian 7591A tubes. I bought a "set" of four, which I received and which appear identical to the my "original" electro-harmonic tubes.

Now my reason for this query: The cross-sectional diameter of the electro-harmonic 7591A units are too large to fit properly in the Sherwood sockets. What gives?

A brief search online suggests to this novice that these modern aftermarket tubes are (duh) fatter than the original electron tubes. I see mention of aftermarket pin adapters so that tubes with similar electronic properties, but different pin patterns, can be substituted. Does such an adapter exist for my Sherwood sockets?

Alternatively, because the shape of the electro-harmonic 7591A glass housings are slightly tapered cones (thinner toward the top) if one had a half-inch tall adapter 7591-to-7591 the Russian tubes would then fit without side-to-side glass contact, assuming I alternated adapters at every other socket position. Does such an adapter exist?

As it stands right now the four "new" tubes contact their respective neighbor, with the outermost (2) tubes unable to fit squarely into their socket. Am I correct in thinking that such glass-to-glass contact is not good for electron tube lifetime? This mechanical interference has to be putting stress on the glass, right? Should I pay big bucks for NOS tubes that fit properly?

Any advise or suggestions will be sincerely appreciated. I guess it's not the end of the world if I have to replace tubes often, but the present arrangement seems pretty lame to me.

Thanks,

Charlie


Hi Charlie,

Glass to glass contact is not great idea. Beyond NOS 7591A's, there are other options. Right up front, I do not have any personal experience with the new production 7591A's, just NOS- but these days, that can be a crap shoot as well. Anyway, JJ makes a 7591A that is the same diameter as NOS so they should fit better. Also, the same company that makes the Electro Harmonix 7591A's (New Sensor) also released a so called "re-issue" Tung Sol 7591A. I believe these are the same diameter as the JJ / NOS but appear to be 2x the price of JJ's. If I were going to new production, I would probably go with the Tung Sols.
The spacer idea is neat but you may have to make those yourself. Use a tube socket and tube base. There was a time when the 6GM5 was an NOS 7591A alternative but had a different base so an adapter was needed. The price of a 6GM5 is up there now an NOS 7591A anyway so the climb might not be worth the view.

BR's,

Mark


THANKS MARK

Just the focused spot-on information I needed. If you ever need any info old hot rods give me a holler.

Charlie
Reply
Thread Tools
Display Modes

Posting Rules

Smilies are On
[IMG] code is On
HTML code is Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Loud buzz on Sherwood S 5000 Ray Smith Tech 1 March 10th 13 11:21 PM
Sherwood S-5000 II Integrated Amplifier Jon Yaeger Vacuum Tubes 1 March 28th 05 06:20 AM
WTB: Sherwood 5000 parts Jon Yaeger Marketplace 1 February 15th 05 04:10 PM
WTB: Sherwood 5000 parts Jon Yaeger Vacuum Tubes 1 February 15th 05 04:10 PM
Sherwood S-5000 II Question [email protected] Vacuum Tubes 0 July 11th 04 09:17 PM


All times are GMT +1. The time now is 03:48 PM.

Powered by vBulletin® Version 3.6.4
Copyright ©2000 - 2023, Jelsoft Enterprises Ltd.
Copyright 2004-2023 AudioBanter.com.
The comments are property of their posters.
 

About Us

"It's about Audio and hi-fi"