• 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.

I'm looking for 6an8 (as V1) schematics

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tricomp

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Joined 2004
tricomp said:
I agree with you calculations of Va ~ 40V of the input-pentode. I arrive at the same conclusion as Ik is close to 1mA. However, measuring the actual voltage with a DVM with an input-R of 10Mohm shows Va ~ 125V. Now, that can't be true, but the scope confirms it and reveals no self-ocsillation that might cause distorted readings. Any explanation?
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No, no, no, I can't believe what I'm saying! Actually that topic came up when I made the amplifier last year; I just forgot.
What I'm measuring at the anode with the DMM and the scope is of course true. The voltage read at the cathode includes screen-grid current so the anode-current is well below 1mA. The Va of 125V is true and therefore the pentode isn't operating quite as bad as first feared.
I'll still try your suggestions out and now I have actually found a complete discription of how to calculate gain of the pentode in this boot-strapped set-up with 'artificially' high anode-load.
More on this later when I am doing the actual suggested 'upgrade', which I hope it will be.

rgds,

/tri-comp
 
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