[Amps] Alpha 76A - 120hz hum on 160m only

[peter chadwick]

I'm guessing a bit here.....but the numbers should be 'ballpark'.

The 'cold' end of the plate choke is bypassed with maybe a total of around 5000pF to ground. That's about -j17 ohms. The plate choke is say 250 microhenries or +j 2800 ohms.  The HV is around say 2500 volts so the plate swing is around 1500 volts rms. This gives around 500mA of RF through the choke, and so the 'cold' end of the choke will be at about 8.5 volts of RF. If you haven't got another choke and bypass  as you work back to the PSU, you're impressing that back on the rectifiers. 

The situation would be worse on 160, of course. something like a small 50 or 50 microhenry choke (even wound on a bit of lossy ferrite) and another bypass - 0.005 or even 0.01 microfarads should help. So would a 50 ohms glitch resistor with a bypass on the PSU side

Of course, you may already have a choke between PSU and plate choke, in which case this is horse feathers...

73

Peter G3RZP