"Antonio Vernucci" wrote in message news:47bf2ba9$0$36443$
My problem is called "tuneable hum". It has nothing to do with filter
capacitors, transformers coupling, cathode to filament leakage, etc.

It only shows up on certain stations. It depends on the path followed by
RF
signal (e.g. if it passes through the rectifiers).

Typical cures a

- bypass capacitor across the power supply rectifiers
- bypasscapacitor between mains and ground.

Tony I0JX


Tony

Have you tried using an external balanced antenna? Is this problem occuring
with a random length antenna wire that is using the AC lines, etc. as the
counterpoise for the antenna system? Some more information on the antenna
might provide some clues. Tuneable hum shouldn't be a problem when
using an external balanced antenna.

Pete k1zjh