[Amps] TL922 problem

[Ron Youvan]

   Steve ZL1BHD Wright wrote:

> 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?

   DC Voltage on the grid (or cathode) can be measured it with a Volt
meter with no drive, compare the two tubes.

   I don't recall RG-85, but if it is suppose to be RG-58  it will pass a
kW as long as the reflected power is minimum, but tune up on the wrong
band and you will toast it.

   Sounds a lot like a bad tube, or you lost a grid RFC on one tube, if
any.
-- 
   Ron  KA4INM - Youvan's corollary:
                 Every action results in unwanted side effects.