Q's about Tubes ("JFETs with pilot lights") Answered
Recently I acquired a couple vacuum tubes for $35, and I gave them about 7V filament voltage, and randomly probed around with a 50V 200mA HP lab power supply to see if I can get them to do anything.
I found that the most I could get was 40mA between the heated cathode and the closest gate on the pentodes, and a few mA when connected "properly". I guess I just don't have a high enough voltage. :/ I don't want to mess too much with direct mains, and I don't have an isolation transformer.
I have a bunch of different tube numbers, although they all look the same to me. (some of them have different inners though!) So my questions are:
* Any cool project ideas? I'm thinking FM radio w/ bluetooth tube speaker thing (obviously w/ a separate module) Maybe a nixie display too??? IDK!
* What do I need to know to get started with messing with them?
* How do I know if I am pushing them too hard or damaging them? I got the anodes glowing, and the current drops proportionally. Bad?
* Most of them are labeled "radio tubes" some probably were in early TVs as well.
* How much current/voltage do these things typically require? Can I do any sort of dark tricks to get them to operate well at or under 48V? I know some tubes were special and can run at 12V due to design.