Answers to various questions

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This is an amplifier I bought that had seen little use. When I baked the tubes as a precaution to degas them, using a low voltage, high current, and therefore a positive grid voltage, I was able to measure that the tubes exhibited "normal" curves like those of Eimac (they are metallic Eimacs). So, apparently, the tubes are not dead.

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Here's the principle of the bias system I use.

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I tested it with a single tube (it's easy) and I'll do it again. What I noticed then was that the gain was lower (why?):

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For only one tube, CW (1900 V)

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9 W -> 100 W? Ia=170 mA (10.4 dB)

23 W -> 200 W? Ia=220 mA Ig=10 mA

39 W -> 250 W?? Ia=230 mA

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For only one tube, SSB (2600 V)

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8 W -> 100 W Ia=180 mA (10.9 dB)

18 W -> 300 W Ia=230 mA (2550V)

31 W -> 300 W Ia=270 mA (2500 V)

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That's why I went back to the two-tube situation.

I don't have any 4-250Zs, and I wanted to stay on the ground grid.