[Amps] TL922 problem

[Steve Wright]

Greetings,

I have a TL922 that has a severe distortion problem - ONLY on the 80m
band.  At full power into a perfectly matched antenna, transmission
starts off quite normal but quickly gets a raspy edge on it and then
descends promptly into the "completely unreadable" territory.  One tube
is running quite a lot brighter - and it even does this with no drive at
all, which leads to thinking there is a capacitor conducting a bit of DC
somewhere in the 80m output circuitry. On 40M I can tune up and push it
hard with 100W drive all day without any hint of the problem.  Other
bands not tested.

The antenna is a RG85 coax-fed dipole at 30ft height with no balun, no
tuner, better than 1.1:1 SWR in the middle of the band, and 20m of coax
laid on the back lawn as an RF shunt outer-to-ground.

Is this just RF coming back down the coax braid outer?

Any suggestions?


Thanks,

Steve ZL1BHD