If you’re old enough you might remember seeing one of these in a drug store, grocery store or even Radio Shack. You could pull all the tubes from your radio or TV, put them in a paper bag, and take them down to your local store to test. And hopefully you wrote down which one came out of which socket. Once you found the bad tube or tubes, the store proprietor would unlock the bottom and find new replacement tubes. And the price list is taped right inside the door.
There are also testers in carry-cases.
And there are companies that sell tube amp kits with very detailed instructions, some based on the Dynaco specs and designs from the 50s-70s. Repro parts are still made. Dynaco sold Dynakits back then.
The tubes are mostly Chinese or Russian made, possibly some in Ukraine.
Thing to remember is they run very high voltages and they can self destruct when one’s back is turned.
This vendor has been around for decades and has a supporr forum… http://tubes4hifi.com/