It's not the first time I've scratch built a TL-922 from a collection of original parts acquired from various 2nd hand parts sources on-line but this is the first time I've attempted to document the process. I started collecting the parts for this project in 2010 or earlier so it has been a slow process for me.
The TL-922 was a well designed and mechanically sound H.F. Linear Amplifier built for the Amateur Bands in the 1980's. It's mechanical construction is equal to or better than any others I have seen offered for sale in that era. The circuitry is very basic and mostly reliable given the thousands of units that would have been manufactured over the years of production. There was no emphasis given to protection circuitry other than the basics. Also of note, is the fact that there were really no changes to the circuitry, if any at all, that I am aware of from the first to last production units. This says something about the quality of the original design!
I bought my first used and broken TL-922 in 1998 and over the last 20 years or so repaired and/or updated many more of these amplifiers for Australian hams that have acquired them on the 2nd hand market in VK. I have also rebuilt at least four of these TL-922 amplifiers from parts acquired on eBay USA and other used parts sites here and overseas. It has not been the cheapest way to go but I have enjoyed the experience and learned somethings along the way.
I'm not an engineer although I am a qualified Radio & Electronics Tradesman with 40 plus years of experience in the commercial Two-Way Radio Industry so I do know about fixing equipment and making gear more reliable.
The original antenna relay is repurposed in the step/start circuit. The 110V/240V taps that reside behind the rear panel inspection cover are removed and rewired permanently for either 110 or 240. A small piece of aluminium sheet can be formed to fit into the compartment and this then holds the step/start components and associated wiring.
As an option, D3 to D7 could be replaced with a NPN transistor and Zener diode to provide tube bias.