This is both a little repository of information about the Kenwood TL-922 and TL-922A amplifiers that I’ve found online as well as a list of repairs I’ve done to my own unit.
Here’s a list of modification sites and what seems good/bad.
W8JI has a great analysis of modifications done to a TL-922. Some are good; some are bad.
As well as a great writeup on protecting your metering circuit and the reasoning behind it.
The modifications that look sensible here include:
However, the suggestion to disconnect the RL-2-1 normally closed contact seems a bit questionable. Others have pointed out that the tube should be biased high when not in use so it doesn’t become a white noise generator. So, perhaps instead a fuse should go between the filament transformer primary and the mains supply.
Now, if you’re interested in where the modifications W8JI disagreed with came from, here’s a great starting point.
There are a bunch of what look like useful and not quite useful modifications here.
The useful modifications:
The 1A 250V fuse in the plate B+ supply seems sensible, but a 250v fuse may not blow clean (ie, it may blow short.) It looks like a sensible idea though in general and finding a 3500v rated 1A fuse seems .. tricky at best.
A 1A slow blow fuse in the filament transformer seems like a good idea. It looks like it is supposed to avoid melting the transformer if there’s a grid-to-filament short.
There are disagreements on the value of that glitch resistor in series with the B+ supply (10 ohm? 22 ohm?) and whether you should also remove the first choke in that circuit. I need to read more and do a bit more math to see what makes sense.
The not-quite-useful modifications:
Note that so far I’ve been unable to find an output power peak using load on 80m and 160m; I may need to re-check the bandswitch and padding capacitors.
Also, don’t try to run the amplifier at the load knob at 0 or 1 right now; it may be too little coupling there and grid current could get a bit hilariously big and cause things to go “pop!”. It can also lead to higher grid current than needed and cause the output to go non-linear. So, don’t do it. Over-couple things a bit and just don’t run too much power too long!
I’ve done the following to my amplifier.
The TODO items.