a lot .
once I replaced the HV caps, screen resistors, cathode resistors, rewound a plate choke, rebuilt a band switch, gave it a complete tune up, and put all the filters in it.
It's essentially a "Gold Label" 830 now.
I do have one aberration. I get a consistent complaint from "one" operator about the "thump" from my MC-50 Mic. If I ask, others will tell me it's there but this one boojum insists on calling attention to it not just every time I join a conversation but every time I unkey!
In case you're wondering the screen laid over and shorted to, well, everything. It wasn't so much abuse as I don't expect much more than 100w on all but 10m. It was just age. Same with the band switch.
CK is fortunate that it's an 820 in at least one way. The external VFO for the 820 is a lot easier to find. Now to find a TL-922A. Yeah there's better but it would at least look at home next to the 830.
The "other" hybrid is the Uniden "Henry" Tempo 2020. That is a whole book of different right up to the 12BY7A and the 6146's. The PA's are essentially the same. (I have three 2020's)
I just like them. A lot.