Re: Valve failures
As the DC conditions are close I would be cautious about your conclusions. Touching a pin does not always result in a response as it depends on the impedance of the circuit at that point. The grid is connected to the IF secondary which has very low resistance, you will only be able to inject noise at the resonant frequency and even that is going to be affected by the probe.
Do you get any noise when you switch between the MW and LW bands? With the waveband switch on MW, measure the voltages on V2.
PS: with this circuit you can tell the valve is conducting as the screen is fed by R7 and it is dropping the correct voltage.
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