Sounds like the classic RF in the shack. 30 feet (of height) is not very far
away from your equipment. Un-plug all other equipment from the radio other
than the amplifier and the microphone. Try a different microphone.
Does a single carrier in RTTY mode without a microphone plugged in sound
distorted over the air? How about CW with a hand key or two pieces of wire?
Lots of stuff on Jim, K9YC's site about using a good balun at the feed point
along with lots of other helpful information.
73
Jim W7RY
-----Original Message-----
From: Steve Wright
Sent: Sunday, September 03, 2017 2:18 PM
To: amps@contesting.com
Subject: [Amps] TL922 problem
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
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