Batboard

I have a UHF N1274A which buzzes after a few seconds on TX. The buzzing is a physical noise coming from the amplifier, not a noise heard through the speaker. Sometimes it only buzzes on unkey. Other times it buzzes continuously on TX. It is less likely to buzz in the morning when it's cool.

Recently my converta-com had a day when a poor RF out connector caused the external amplifier's load-sensing relay to wildly click as it opened/closed rapidly. The amp started buzzing shortly after this. Power output is also down, from about 25W to 18.

Before I open the case, any pointers what I should be looking for?

Thanks,

T

Likely there are some high valued electrolytic capacitors in the circuit usually for A+ to ground and/or bias circuitry to ground. Usually these are there to supress low frequency(audio) oscillations. I would start by checking/replacing the two or three of these that are part of low frequency decoupling networks.
I have tuned RF amplifiers in the past using a sweep generator and spectrum analyzer/scope-diode detector and had these capacitors literally blow up(they don't like the rapid charge-discharge that occurs when RF is repeatedly reapplied to the amp).

After much experimenting, I'm ready to conclude: It's the radio, not the amp.

The converta-com wasn't charging the HT properly, and on TX the power output was very low, under 1 watt. With low power in, the amp would drop out, causing the buzzing.

A fresh battery in the HT cured the problem. This converta-com seems to perform a whole lot better, by the way, when the radio is not left in it - even when the radio and converta-com are both off. Leave it out and it acts happier. Too bad; I had wanted to lock it when not in use.

Thanks for suggestions offered.