Most of the strong AM signals received on my National HRO are affected by hum.

I put a ceramic capacitor in parallel to each of the 80-type vacuum diodes
with no noticeable improvement. Does anyone remember which other cure was
proposed to solve the problem?

Before someone gives me a simple answer, I confirm that the electrolytic
capacitors were checked to be good and the DC HV is perfectly filtered. No hum
in absence of signal.

73

Tony I0JX