$3 tube amp bias probe....

[electra225]

....made in under 30 minutes. I think I'll build one of these. You could do the same with a miniature if you used a test socket. Neat idea, and cheaper than buying a ready-made one.

https://www.youtube.com/watch?v=WjhNSbQI_9M

[TC Chris]

Nice link.

Chris Campbell

[electra225]

Would we need two of these if we were working with push-pull amps? Many of the ones you see pre-made are sold in pairs.

[TC Chris]

Likely just a matter of convenience, to avoid turning off/moving to other socket/turning on, then repeating until they're biased equally. But unless you had two meters, you'd be turning off/on anyway.

Chris Campbell

[electra225]

I have the stuff to make two and I have a couple old digital meters I don't really use anymore. I need to figure out how to do this with miniatures without using a spendy test socket. Getting a usable base from a miniature tube will be the issue. Wonder if you could use a glass cutter to take a miniature tube apart, or would it implode when you penetrated the glass envelope?

Maybe these would work economically for the miniature tubes.

https://www.ebay.com/itm/201096401982?h ... R8r_7urTYg

[TC Chris]

Or bypass the tube-base component altogether. Just solder some solid wire onto the new socket, same gauge as tube pins. Cut a little disc of plastic or wood, drill a circle of holes in the same pattern as the tube base socket, epoxy it to the wires.

Chris Campbell

[electra225]

I think the idea of the base is so you can isolate the plate pins. You measure current in series with the plate pins.