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variacs come up on ebay now and then. if you have a surplus store near by they sometimes have them.
the best ones are really a lot more than just a variac, I have one that has a meter on both the output voltage, current and its isloated from the line with an isolation transformer.
a standard variac is just a variable tapped autoformer, and provides NO isolation from the line. you can vary the output from 0-140vac (approx) but you still have to be careful since one side of the output will be hot with respect to the ground. Your set has a power transformer so this isolation takes place there, but on other sets this may or may not be the case.
Back in the day manufactures would incorporate interlocks that would prevent the set from geting power with the backs removed due to the shock hazards of lack of isolation from the mains (transformeless sets) and the metal chassis was always mounted in such a way as to prevent any metal screws from contacting the metal chassis and being exposed. this is also why its important to not replace plastic knobs with metal ones on some sets.
A reg autoformer variac isi fine as long as you are aware of the shock hazard and you have some way of monitoring the circuit being powerd up. Again the best way to do this IMHO is a voltage and current reading on the B+ right off the output of that 5U4.
Tube testers are on ebay all the time, but of course the operating status is a big gamble. If you mainly want to do TV works then I would stick with a later model emission tester, something that can test the later compacton tubes.
google tube testers, there is a good site, lizard tales or somethng like that that goes into great detail on testers.
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