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In Reply to: RE: Looking to build a 6V6 amp! Thoughts? posted by mikeyb on August 15, 2014 at 12:18:18
DHT's. Just want a simple amp. Other suggestions would be nice!
Follow Ups:
O.K. Getting back to your original question, I usually separate the power supply from the amp using separate chassis, and interconnect them with a cable of less then 3 feet in length. Unless you can find a magnetically shielded power transformer, the fields around it can couple into other components (e.g., output and interstage transformers). I've done it both ways, but prefer separate chassis. I built a stereo amp with separate power transformers\chokes for each channel on a single large chassis. It weighed a ton and got really hot.
The speakers you settle on have an ENORMOUS influence on everything else.
I gave you some ideas for a no GNFB triode wired design. It will sound fine, but 2 WPC is all there is. If you employ speakers whose sensitivity is in the 94 to 96 dB. range, look to a full pentode setup that uses regulated g2 B+ and employs both Schade and global NFB. The bulk of the NFB should be in the short, Schade, loop. Only a few dB. will be needed in the outer, global, loop.
Whenever GNFB is employed, use a 1 pole high pass filter that "corners" in the 15 to 18 Hz. range, to gain protection against O/P trafo core saturation. Suppress infrasonic trash! Also, employ high gm small signal types. High gm provides resistance to HF error correction signal induced slew limiting.
Eli D.
I built a push-pull 6V6 ultralinear amp with used Dynaco Z-565 outputs and a single, current-sourced, long-tail differential 6SL7 driver. I used some 0.22uF Facon paper-in-oil coupling capacitors.
There's barely enough excess gain to provide any negative feedback. The amplifier has a nice midrange but sounds pretty shut-in. I might try changing to poly coupling caps to see if it opens up a bit. The amp makes about 11 Watts per channel.
This was a junkbox project and I've never tried to optimize it. It was supposed to be a loose adaptation of Poindexter's "Musical Machine."
IMHO, not really a success. Listenable, but not extraordinary. I know, not what you were looking for, but sometimes it's good to have a data point, even if it's not a positive one.
I think adding another stage of gain would lower the distortion and give a more incisive sound. If you're going to run almost pure open-loop, you probably want a very linear output stage. And a more robust driver tube.
LOL.
-Henry
Henry, that's a very clean layout. A shame to see it sitting idle just because the first rendition didn't wake up. Have you made basic measurements like frequency response and the like? Much as I like octals, I believe 6BQ5s produce better dynamics than 6V6 in PP designs. Can't prove that, it's just my gut feel after years of hearing both.
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Buy Chinese. Bury freedom.
Thanks. The amps haven't gone to waste. I sold them to my friend, Bryan who was using them in his system which is notably more high-end than mine. About a year ago I brought my new solid-state amplifier over to his house and it sounded so much better I took pity on him and gave it to him on semi-permanent loan. I use the tube amps to watch movies on my TV.
The amps aren't horrible, they just don't have that "sparkle" or "see-through transparency" of the solid-state amp.
-Henry
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