[Amps] TL922 problem

[Jim Thomson]

Date: Sun, 3 Sep 2017 22:40:27 -0700
From: Jim Brown <jim at audiosystemsgroup.com>
To: amps at contesting.com
Subject: Re: [Amps] TL922 problem

<On 9/3/2017 12:18 PM, Steve Wright wrote:
> Is this just RF coming back down the coax braid outer?

<Very unlikely. More likely related to one tube running much hotter than 
<the other.

<73, Jim K9YC

##  But he just stated that the tubes run balanced on 40M.  What he needs is a
dummy load, then test it on 160-10m, and see what happens. 

##  The TL-922 has the filaments  wired in SERIES, with 10 vac across the series
filaments. 

##   IF one of the grid chokes went open, you would have NO path for DC grid current 
for that one tube.   IF one of the grid bypass caps is semi flaky, you can get distortion and RFI.

##  Ideally you want to remove ALL the  grid bypass caps  and also the RF grid choke from each tube. 
Then bond all 3 x grid pins to the chassis..for each tube.

##  he could also swap tubes and see if the brighter tube follows or stays put.  But if the amp runs fine on 40m,
and unbalanced on 80m, it could be the use of NO balun at the ant,  ant too close to the shack, etc.  I have see
that once before, where RFI etc existed on 80m, cuz of a lousy balun at the 80m yagi.   Quick fix was to use  30 inches
worth of bead baluns, slid over 213 coax... right at the output of thr amp, problem solved. 

##  seen  a similar issue on 6M, where severe distorted audio resulted... cuz of a lousy balun used.  Again  the temp quick 
fix was to us a string of beads over 213u.... right at the output of the 6m amp. 

##  In his case,  audio starts off good, then deteriorates quickly.  It could be a bad grid cap, grid choke, or perhaps a 
80m padding cap if the 922 uses a padding cap for either the  tune and or load cap...  and probably no padder at all on
40m band, which might explain why its good on 40m.   It could also be lousy padder contacts on  80m. 

##  It could also be lousy bypass caps at the cold end of the fil choke, or at the base of the plate choke.

Jim   VE7RF