I have been working on a Philco 49-905. I had concerns about its 35c5 audio output tube. I checked it, and then checked about 5 more in two of my tube checkers. The others were NOS tubes. They all showed shorted and bad emissions, etc. I triple checked my settings on both checkers. Is there something I'm doing wrong.

Also, could I sub a 50C5 for that one?

Thanks,
David

Sure can. Will help with the increased line voltage we have now. Just curious, test a 50c5 on the same tester. Same results?

David

A 50C5 will work. Good idea if line voltage is high. It just takes longer to heat.

You mentioned tubes are NOS. Are you sure? These tubes will get heater to cathode leakage after a lot of use.

I recently acquired a lot of tubes from an old TV shop. As far as I can tell, these 35C5's are not used, but then, how do you know? Thanks for the fast response.

If the tube matches the box it's in, you have a better chance of a good/NOS tube. Some techs replaced weak tubes, and they can be used in certain set just fine. A tester, and a radio are your best bets!