Good morning.
I’ve just purchased over a thousand second hand and nos, various vacuum tubes.
Obviously there are quite a percentage that have no, or only partial identifying numbers.
Is there a way to test a tube to find out what tube it would be matched to, or being unmarked are they useless??
Cheers Darren
GE manufactured tubes are etched into the glass, so luckily they will always have identification. The others are not uncommon to lose their writing. RCAs have a circular box around the number. There are a few ways to ID a tube if all else fails. Depending on the lighting, you may see a faint outline where it was. Use your breath to add some “fog” to the glass, this could make it appear. Worst case, you can determine style and pinout then figure out the elements inside. Then you go to your reference material (I have a few tube books) and see what comes close. Also you could carefully use a power supply on the filaments to get an idea of heater voltage.
I have a number of these tubes, if anything they are great visual effects haha
Radios + Tubes + Scopes + Cars= Nothing better!