Mutron III type Vactrol build.

[digi2t]

You are all welcome.

I had a ton of stuff on Photobucket, which as we all know, went poof over night. If there are any other of my past posts that you come across that you would like pictures re-upped to, just let me know.

Cheers.

[Bigbadwolf68]

Before capping the ends, you can also test to see what kind of resistance you will need to set the range. By testing on a breadboard, you can swap different resistors, turn out the lights, and then see the LED light up through the epoxy. Once you've figured out the resistance range, you can cap it.

You lost me there... would you mind elaborating on this particular procedure?

[digi2t]

Before capping the ends, you can also test to see what kind of resistance you will need to set the range. By testing on a breadboard, you can swap different resistors, turn out the lights, and then see the LED light up through the epoxy. Once you've figured out the resistance range, you can cap it.

You lost me there... would you mind elaborating on this particular procedure?

With ends uncapped, you'll be able to see the LED light up, and how intense it gets. With the vactrol in place, and with lights out, you get a visual sense of the how much resistance you'll need to set the right range. Too high, and you're into dog whistle territory. Too low, and there won't be any whonk. This is all dependant on how bright or dim the LED ranges. Having a visual clue makes it easy to figure out whether you need to go up or down in resistance. It's also a good check to make sure that the darned thing works!

[Audiotrove]

I'm in the midst of troubleshooting and repairing a 1973 Mu-Tron III.  While this Vactrol build is genius and looks like it's pretty straightforward, I'm really hoping this 1973 version is still working: