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In Reply to: more posted by Lew on February 14, 2006 at 08:20:50:
Lew, got it. Thanks for the clarification. A 6sl7 might make a better CCS because it has more gain but I don't think it will stand up to the current. Well, maybe. It's really plate dissipation, not current and with it in the cathode circuit the voltage would be low so...that might be fine.
Thanks again...Tre'
Have Fun and Enjoy the Music
"Still working the problem"
Follow Ups:
I agree. The plate dissipation of an SL7 is something I no longer can quote without looking it up, but I think it would be a stretch to use it as a CCS in an Atma-sphere. I don't know how much current is now being used in the dual-differential cascode, but lets assume at least 2mA per phase for a total of 4mA seen by the CCS, more likely it's higher than that, and then too one has to be able to bias the SL7 within the -300V available from the B- supply. But if it works, it works.
Here's the link to the original discussion. I see Lew had his doubts back then, also. Thanks for the replies, Tre' and Lew, I do appreciate them.Frank
"Here are some tweaks if you want to use the 6SL7 as the V3 CCS tube:Change the cathode resistor on V3 pin 3 to 32K.
Add a second 47 volt zener diode in series with the first on the grid of V2, raising the grid voltage up to roughly 90 volts. The 499K resistor could be changed too (but its not too critical) to 332K or thereabouts.
Distortion is further reduced and dynamic range is slightly improved.
Finding decent 6SL7s is a problem- most of the current production tend to be microphonic. This is a problem in the circuit as microphonics in the CCS tube are definately audible. "
I would say if you follow the above it should be better than stock. But you need to make the circuit changes not just throw the tube in.
Tre'
Have Fun and Enjoy the Music
"Still working the problem"
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