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Okay, typical operation shows 105 V both plate and screen, resulting in 43 mA plate current, 4 mA screen current and about -5V control grid bias.
The tube simply will not work with such a low screen voltage, I firmly believe.
Estimating 4 mA screen current, add about 10k or so from screen to B+, then capacitively couple the audio to the screen. This will require a substantial audio signal, perhaps 20V, not easily obtained from every audio generator and certainly not from a microphone or phono pickup. So a 'speech amplifier' is needed.
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