"Antonio Vernucci" wrote in message
...
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?

73

Tony, I0JX

Tony

I'm assuming you're talking about tuneable hum, where the AC line frequency
modulates the received carrier.

Does the receiver have AC line bypass caps from each leg of the AC power
to the chassis? Have you tried grounding the chassis to a good earth ground
to see if the hum modulation level is reduce? If grounding helps, you
should
check to see that the bypass caps are installed. Also adding ferrite snap on
cores on the power may help along with the ground connection.

pete k1zjh