[Station X]

The only non-electrolytic capacitor known to fail in these receivers is C34, the audio coupling capacitor, which I know for a fact you've changed in one of your receivers. It's also been explained to you how to test this capacitor by checking that there's no positive voltage on the control grid of the audio output valve.

Only replace the electrolytic smoothing capacitors if they're leaking electrolyte, get hot, or there's excessive mains hum.