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#1
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6AS7 Triode PP Amps-experience?
I was doing some housecleaning and came across the old Audio Anthology
with C.G. McProud. He really likes 6AS7's, but usually with transformer-coupled drivers. The driver xfmr would cost a lot plus, phase shift makes applying feedback difficult. Has anyone built a nice 6AS7 resistance-coupled amp recently with good results? I'm thinking they are good for ten watts with a single tube in push-pull. |
#3
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Yeah, I'm going to build a 6AS7 amp on a testbed (not pretty) basis
using an existing power supply I built for another amp, and if I like it it may become part of a concept amp I've thought about for awhile. I'm thinking of putting a 6AS7 triode PP channel and a pair of big beam power tubes on one chassis with the electronic x/o. That would be great for a two-way (Altec 604s) but I'm using three way speakers-I think the bass will get its own channel and the mid and tweeter will share the small one with an optimized passive x/o. Just a thought. |
#4
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wrote in message oups.com... calcerise wrote, I was doing some housecleaning and came across the old Audio Anthology with C.G. McProud. He really likes 6AS7's, but usually with transformer-coupled drivers. The driver xfmr would cost a lot plus, phase shift makes applying feedback difficult. Has anyone built a nice 6AS7 resistance-coupled amp recently with good results? I'm thinking they are good for ten watts with a single tube in push-pull. John Stuart designed a bootstrapped driver for the 6AS7 output contact Mr Stuart...................GC |
#6
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"george craig" a écrit dans le message de news: ... wrote in message oups.com... [ . . . ] John Stuart designed a bootstrapped driver for the 6AS7 output contact Mr Stuart...................GC Indeed, he is the King ;)) Cheers, Yves. |
#7
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The Glass Audio CD has been on my list of things to order for some
time now, so I will, and not bother you until I have it in front of me if at all. |
#8
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I made a simple 6AS7 PP amp based on a modified Williamson schematic like
this: - a gain stage (1st half of a 2C51/Russian 6N3P, unbypassed cathode resistor) - a DC coupled split-load phase splitter (2nd half of the 2C51) - a choke-loaded driver stage (Russian 6N1P loaded by 80H, 20 mA chokes, unbypassed common cathode bias resistance like in a differential amplifier) - 6AS7 (Svetlana 6S13P) operating in fixed bias at about 230V a-k and 52 mA into a 2K5 a-a load; bias voltage needs to be about -130V with WIDE regulation capability, I found discrepancies like -80 to -150V among the two triodes in the same glass bulb. The driver stage, being choke-loaded, is fed at about 200V / 6 mA per triode and delivers a voltage swing of about 300V peak-to-peak. The only DC feed is provided by a SS bridge thru a CLC filter (100uF/4H/100uF) and then divided between the two channels by a RC filter (47R/220uF per channel). No feedback is used, but some can be introduced (right now sensitivity is about 0.8V p-p for full power). The amp delivers some 14-15W with a very "dynamic" sound and good bass extension due to the very low internal resistance of the 6AS7 tube. Nevertheless it is not an audio tube and its linearity is not as good as (say) a 6B4G, therefore now I'd prefer build a similar unit using a PP pair of these DHTs instead, having lower bias and driving requirements. Ciao Fabio ha scritto nel messaggio oups.com... I was doing some housecleaning and came across the old Audio Anthology with C.G. McProud. He really likes 6AS7's, but usually with transformer-coupled drivers. The driver xfmr would cost a lot plus, phase shift makes applying feedback difficult. Has anyone built a nice 6AS7 resistance-coupled amp recently with good results? I'm thinking they are good for ten watts with a single tube in push-pull. |
#9
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The 6AS7 is specifically not rated for fixed bias use, and generally
most people follow the admonition in all tube manuals against this practice. Simplicity and availability are the motivations behind building 6AS7 amps. The 6B4G is an expensive tube since they are in demand among audio people. (Although many have no knowledge of how to use them, or any other tube for that matter.) |
#11
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#12
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wrote:
I was doing some housecleaning and came across the old Audio Anthology with C.G. McProud. He really likes 6AS7's, but usually with transformer-coupled drivers. The driver xfmr would cost a lot plus, phase shift makes applying feedback difficult. Has anyone built a nice 6AS7 resistance-coupled amp recently with good results? I'm thinking they are good for ten watts with a single tube in push-pull. I used a 400 volt plate supply & cathode bias. Each cathode really does need to have its own resistor to prevent thermal runaway. I tried a common cathode resistor but managed to quickly burn a hole thru one of the grids. Ik for each triode is 52 ma. You could also use bias servos if ambitious! The plate-to-plate load is 2150R, a special made for me by Hammond based on their 60 watt 1650N. There is no need for an IT at all. Nor is the driver circuit complicated. At 10 watts & zero NFB the 2H is down about 45 db while the 3H is down about 42 db. At 25 watts & zero NFB the 2H is down about 38 db while the 3H is down about 28 db. In the final version I used 13 db NFB so that the resulting THD & IMD results were quite good. Clipping occurs at about 30 watts in this arrangement. The 2nd article shows how the circuit can be modified so that the bootstrapping is done without the benefit of UL connexions on the OPT. I've never seen either of these driver circuits ever used to drive low mu triodes by others previously. I believe it to be unique & original. Its simplicity will surprise you! For more information on biasing the 6AS7/6080 family see http://frank.pocnet.net/sheets/030/6/6080.pdf Page 4, Note 6. Cheers, John |
#13
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Calcerise wrote,
wrote in message oups.com... I was doing some housecleaning and came across the old Audio Anthology with C.G. McProud. He really likes 6AS7's, but usually with transformer-coupled drivers. The driver xfmr would cost a lot plus, phase shift makes applying feedback difficult. Has anyone built a nice 6AS7 resistance-coupled amp recently with good results? I'm thinking they are good for ten watts with a single tube in push-pull. Here is another reg. tube amp www.wdehaan.demon.nl/mono/6336.html ...................GC |
#14
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"george craig" said:
I was doing some housecleaning and came across the old Audio Anthology with C.G. McProud. He really likes 6AS7's, but usually with transformer-coupled drivers. The driver xfmr would cost a lot plus, phase shift makes applying feedback difficult. Has anyone built a nice 6AS7 resistance-coupled amp recently with good results? I'm thinking they are good for ten watts with a single tube in push-pull. Here is another reg. tube amp www.wdehaan.demon.nl/mono/6336.html ...................GC That's a "404" here............. -- "Audio as a serious hobby is going down the tubes." - Howard Ferstler, 25/4/2005 |
#15
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Sander deWaal wrote: "george craig" said: I was doing some housecleaning and came across the old Audio Anthology with C.G. McProud. He really likes 6AS7's, but usually with transformer-coupled drivers. The driver xfmr would cost a lot plus, phase shift makes applying feedback difficult. Has anyone built a nice 6AS7 resistance-coupled amp recently with good results? I'm thinking they are good for ten watts with a single tube in push-pull. Here is another reg. tube amp www.wdehaan.demon.nl/mono/6336.html ...................GC That's a "404" here............. I got that too. But got in via http://www.wdehaan.demon.nl/ Then look down the page to the 6336 link. It works OK. Cheers, John Stewart |
#16
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"Sander deWaal" wrote in message ... "george craig" said: I was doing some housecleaning and came across the old Audio Anthology with C.G. McProud. He really likes 6AS7's, but usually with transformer-coupled drivers. The driver xfmr would cost a lot plus, phase shift makes applying feedback difficult. Has anyone built a nice 6AS7 resistance-coupled amp recently with good results? I'm thinking they are good for ten watts with a single tube in push-pull. Here is another reg. tube amp www.wdehaan.demon.nl/mono/6336.html ...................GC That's a "404" here............. Try http://www.wdehaan.demon.nl/mono/mono/6336.html -- "Audio as a serious hobby is going down the tubes." - Howard Ferstler, 25/4/2005 |
#17
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"Fred Thompson" said:
Try http://www.wdehaan.demon.nl/mono/mono/6336.html Thanks Fred (and John, too) . I was too lazy do do that myself :-) -- "Audio as a serious hobby is going down the tubes." - Howard Ferstler, 25/4/2005 |
#18
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RC-something-which one?
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#20
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"John Stewart" a écrit dans le message de news: ... wrote: RC-something-which one? AFAIK the referenced circuit appears only in RC-16. The tube driving the 6AS7 is a 6SN7 running 450 volts on its plates. Somewhere in my pile I have copy of an article describing the circuit. The description is not in RC-16. JLS Perhaps this one (just one page, there is 16-12 printed at top left corner) www.dissident-audio.com/Yves/276.gif Yves. |
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