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.
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