• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Help with 6SN7 preamp

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I agree with Tom’s advice on layout ease. But if the two channels are side-by-side, you might entertain using one section in each tube for each channel. Channel separation will suffer, but if the rest of your layout is decent, not by much. The second tube would then have the two channels’ CFs, and its heater could be biased separately from the first tube’s heater, to the same voltage as the cathode or just above.

Unsolicited comment on this oft-posted circuit: Whenever you have a cathode follower “following” a common cathode stage, try to connect the CF grid directly to the plate. The voltages usually can be worked out. You may have to diddle with the resistor value in the CF cathode to keep quiescent current the same. This avoids passing the signal through the second coupling cap. Obviously you won’t then need the 220K, and the 820 and the 10K become one new resistor (or maybe a CCS). The note on the bottom about a stepped attenuator makes no sense to me. If you can be reasonably sure that you have no source component with DC on the output, then leave out the first coupling cap, but keep the 1M resistor to ground on the first grid as a safety resistor, no matter whether you use a pot or a stepped attenuator as a volume control.
 
An externally hosted image should be here but it was not working when we last tested it.

i would like to use this ps .i would leave out r1 r2 and c1 c2 and connect r19 to the 250v b+ .what bias voltage do you recomend.
i want to use 5y3 instead of 6ca4 so i will have to learn how to use duncuns psu program to get right part values,this ps is from ax84_m35 filaments will be the 6sn7 not tubes shown
 
Brian Beck said:


...Whenever you have a cathode follower “following” a common cathode stage, try to connect the CF grid directly to the plate. The voltages usually can be worked out. You may have to diddle with the resistor value in the CF cathode to keep quiescent current the same. This avoids passing the signal through the second coupling cap. Obviously you won’t then need the 220K, and the 820 and the 10K become one new resistor (or maybe a CCS).


So you are suggesting to direct couple the stages and do away with the bootstrapping of the second stage while possibly replaceing the cathode resistor with a CCS? I have never CCS'ed a direct coupled stage before. With a CCS, how would you go about insuring the correct DC bias reference voltage for the secong stage considering the high DC coming off the plate from the first stage?

Would LEDs in the CF cathode be a viable option here?
 
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