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#1
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Dynaco Stereo 70 all original?
How can I tell if my Dynaco Stereo 70 is all original? I have searched
the internet but I have not found specific things to look for. I have found plenty of mods that I am not interested in though. |
#2
Posted to rec.audio.tubes
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Dynaco Stereo 70 all original?
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#3
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Dynaco Stereo 70 all original?
Both of the above replies are dead-on.
But, what parts concern you as to 'originality'. Let's go down the list from 'real' to 'silly': Transformers: These are about the _only_ parts other than the chassis and cover that should concern you in any way, shape or form as to their originality. There are several schools of opinion on the quality of OEM Dynaco Iron. Mine is that it is pretty good, if the rest of the system is pretty good. But (especially) the power transformer is marginal if other components are failed or failing. Tubes: Well, gee whiz.... this would be a function of use and/or abuse. Low use & proper bias = good tubes (if good originally). They would decline from there. Boards: Phenolic boards Bad. Glass boards Good. Phenolic boards Bad. Glass boards Good. Phenolic boards can be rebuilt and made reliable. But OEM even with light use are NOT trustworthy. Period. Depending on what your time is worth, replacement glass boards are cheap. Selenium Diode: Good, bad or indifferent, get rid of it. No ifs/and/buts. Main Filter Cap: Moving target. If the unit runs without even a trace of hum and if the cap stays cool (relatively), then it is likely OK. My direct experience with 40 year old electrolytic caps used in this manner is that they are about to fail if they have not already. Consequences of failure could be anything from a bad smell to destroyed iron.... Bias Supply Caps: As above. Failure here could eat expensive output tubes and conceivably output transformers, a bit of a stretch. Switches and plugs: Your call. All other components on the boards: resistors, caps, etc. Replace the caps. Check _each_ resistor. The caps fail and the resistors drift. Peter Wieck Wyncote, PA |
#4
Posted to rec.audio.tubes
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Dynaco Stereo 70 all original?
':
Transformers: These are about the _only_ parts other than the chassis and cover that should concern you in any way, shape or form as to their originality. There are several schools of opinion on the quality of OEM Dynaco Iron. Mine is that it is pretty good, if the rest of the system is pretty good. But (especially) the power transformer is marginal if other components are failed or failing. The transformers are of good materials and workmanship but the power transformer is underrated and unless the amp is modified for much lower load it will die in a few years of serious use. It can be removed and repurposed. The opt's are assymetrical for DC resistance on the primaries and thus will never be really good in performance. For what misguided yupsters are paying for ST70s on ebay one can have a chassis built and buy a good power and two good output transformers. Just a thought. (Power transformer for late Twin Reverb works great and can be had for $50 if you have dealer account, easy to get, from guitar vendors). If you could get one for $50 it would be good for education but.... Tubes: Well, gee whiz.... this would be a function of use and/or abuse. Low use & proper bias = good tubes (if good originally). They would decline from there. Boards: Phenolic boards Bad. Glass boards Good. Phenolic boards Bad. Glass boards Good. Phenolic boards can be rebuilt and made reliable. But OEM even with light use are NOT trustworthy. Period. Depending on what your time is worth, replacement glass boards are cheap. Suspend the OEM board from a tree or stand and hit it with a 28 gauge shotgun from ten feet. It shatters beautifully. Selenium Diode: Good, bad or indifferent, get rid of it. No ifs/and/buts. Agreed, but it is toxic. Store or dispose carefully. Main Filter Cap: Moving target. If the unit runs without even a trace of hum and if the cap stays cool (relatively), then it is likely OK. My direct experience with 40 year old electrolytic caps used in this manner is that they are about to fail if they have not already. Consequences of failure could be anything from a bad smell to destroyed iron.... The telco grade ones in Marantz sometimes reform beautifully (but the consequences of failure are also much higher). The old ones in Dyna must be summarily executed without mercy or hesitation lest other parts die. But since they are all obtainable... |
#5
Posted to rec.audio.tubes
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Dynaco Stereo 70 all original?
I'm concerned with its value. Wouldn't it be worth more in all
original condition? What can be changed without hurting the resale value? For what misguided yupsters are paying for ST70s on ebay... I guess that's me. I was told the ST70 would be a good first tube amp. I hope they are right. |
#6
Posted to rec.audio.tubes
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Dynaco Stereo 70 all original?
The transformers are of good materials and workmanship but the power
transformer is underrated and unless the amp is modified for much lower load it will die in a few years of serious use. Bret, you keep trotting out this tired old mule at any excuse, sometimes even spontaneously. Define 'a few years' and 'serious use'. I know of one of these beasts that has been run (and is still being run) about 12 hours/day, six (6) days per week, lo these last 8 years of my knowledge, and some more-than-a-few years before that I am told reliably. 4 years ago, I retubed, cleaned up, recapped and rebiased one for a friend that had been going about 3 hours/day, 7 days a week, for 10 years, and is still going strong. And he never adjusted anything at all since he got it from the original owner/builder. Purely anecdotal, I admit... but sure not what you suggest or imply. Put another way, I have yet to see a bad power-transformer on an ST-70. Several fried OPTs, due to user-idiocy, but never a bad power-transformer. Anyone else here? Peter Wieck Wyncote, PA |
#7
Posted to rec.audio.tubes
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Dynaco Stereo 70 all original?
CamMan wrote: I'm concerned with its value. Wouldn't it be worth more in all original condition? What can be changed without hurting the resale value? I don't know. It well may be they are more valuable 100% original. They sure as hell aren't listenable that way. I think some of the more well known PCB conversions have reasonable resale and if you save the original board and parts you could always put it back. For what misguided yupsters are paying for ST70s on ebay... I guess that's me. I was told the ST70 would be a good first tube amp. I hope they are right. Well, years ago when they were giveaway items they were right. Today there is no real good old amp I know of you can buy cheap (at fair market value) and learn on. I would build a popular design from scratch for maximum learning value maybe even one of the little EL84 designs floating around. The Mullard book AudioXPress sells gives very explicit construction details including the chassis size, tag board wiring, so you _could not go wrong_ with that. Personally I hate EL84s for hifi but they are small and inexpensive and okay for educational purposes. A lot of people who like what I call "****slobber" or "cow****ed sound" LOVE EL-84s. (I am always taken to task on that.) You could even start out with using a pair of cheap guitar amp OPTs and upgrade later to minimize your investment. Ya gotta pay your dues to play the blues. Some people think I'm a horrible jerk, but although I concede you could take umbrage with the presentation, you know in essence I'm right as to the consequence. Of course people knew Goldwater was right, too, and he got his ass beat to all hell! |
#8
Posted to rec.audio.tubes
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Dynaco Stereo 70 all original?
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#9
Posted to rec.audio.tubes
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Dynaco Stereo 70 all original?
I guess that's me. I was told the ST70 would be a good first tube amp.
I hope they are right. They are. But not if nothing has been done to it since it left the factory. That is an inevitable and spectacular failure waiting to happen. But with a modicum of basic soldering skills and a few bucks worth of common and easily available parts, they can be made both fit for polite society and also quite sweet-sounding. They also happen to be quite forgiving of other than deliberate idiocy, despite Bret's representations. If you want to be walked through it (the ready-for-polite society routine), Curcio Audio does a nice job of that. Peter Wieck Wyncote, PA |
#12
Posted to rec.audio.tubes
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Dynaco Stereo 70 all original?
My Stereo 70 is 45 years old and I am the original owner. I purchased
and assembled a kit in the spring of 1961, my freshman year in college. The amp has been used for 45 years. Since retirement 6-7 years ago the amp has been used 8-12 on most days. I'm listening as I write this note. A few tubes have been replaced over the years as I have moved 7 times. About 8-9 years ago the amp was recaped (and maybe an output tube replaced, I'm not sure); the boards were checked and any trouble spots fixed. I'm hoping it will run another 45 years. The matching PS2 has on had the selenium rectifier fixed. Gary Spear |
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