What do you use to hold a bias pot in place?

[DrGonz78]

I am wondering what sort of sealant you would use to hold a bias pot in place so it won't vibrate and change over time. I have read of using silicone, hot glue or even nail polish to do this. What would you use to just dab a bit to hold the shaft in place?

[g1]

Nail polish.

[DrGonz78]

Nail polish.

Any specific color . Just kidding!! Okay I thought that would work good too, but I wasn't sure if silicone or something was more preferred.

[Leo_Gnardo]

In cases where I can't use the Fender style CTS kind of panel mount pot, or don't want to drill extra holes in the chassis to fit one, I use what I call the "blue cube," a Bourns trimmer resistor. Here's the Mouser part # for the 10K version: 652-3386W-1-103LF . Regardless of the picture they show you, in this version there are 3 wire terminals out the side. It measures approx 1/2" square, or 1.2 cm for the rest of the world. Besides 10K, there are lots of choices for you. I keep a few 20K & 50K besides the regular 10K. A pea size dab of RTV holds the trimpot body in place. I've never had a problem with the adjustment walking off from where I set it.

Those trimpots like the Piher types you find in modern Fender Hot Rod Deluxe & similar, it looks like Fender schmears a wipe of pink nail polish on. Good enough for me. Go to the ladies' cosmetic section & pick your favorite color. I can't decide between plaid or paisley...

[DrGonz78]

I got some hot pink color on hand!! I swear I don't use the stuff on a regular basis either

[Leo_Gnardo]

I got some hot pink color on hand!! I swear I don't use the stuff on a regular basis either

I'm sure! Maybe I'll settle down for fluorescent safety yellow-green. Popular color lately. Lots of folks wearing Tshirts in that shade in the last couple years. "Don't pretend you didn't see this!"

[DrGonz78]

Gotta a glow in the dark version too but that might be a little extreme.

[g1]

Any specific color . Just kidding!!

I got some hot pink color on hand!! I swear I don't use the stuff on a regular basis either

That is actually what I use (or some pink variant). I needed some 'loctite' variant some 25 or so years ago doing field service. I asked the guy if he could find me some nail polish. He asked around and brought me a pretty much full bottle and I'm still using it.
a) when I see it in an amp I know I was in there before.
b) a dab in a non-obvious spot on tools acts as a recognizable mark as tools tend to 'wander'.

[John_H]

In cases where I can't use the Fender style CTS kind of panel mount pot, or don't want to drill extra holes in the chassis to fit one, I use what I call the "blue cube," a Bourns trimmer resistor...

Those were specified on the parts list for a pedal that I have in queue. Thanks, I'll use your nickname for them.

[SoulFetish]

If you want/need to use a panel mount potentiometer for a bias control (Which I use on the back panel of my amp), these offer a lot of security and flexibility in choosing parts.

https://www.alliedelec.com/product/a.../181/70927380/
These particular ones are manufactured by HH Smith/Abbatron, but I've seen other variants as well. The ones I currently use, I must have acquired in some bulk parts deal at some point. They work a little differently in that they are molded composite material which screws onto the bushing, exposing just the tip of a slotted shaft. It uses friction to prevent any the shaft from rotating.

[Leo_Gnardo]

They work a little differently in that they are molded composite material which screws onto the bushing, exposing just the tip of a slotted shaft. It uses friction to prevent any the shaft from rotating.

Way back when I bought a box of Allen Bradley Ohmite pots, all sorts of values. Many had this locking feature, handy for bias adjustment. BUT none of them were values handy for amp biasing. Anybody need a 500 ohm locking pot, heavy duty mil spec? I got a box half full...

[Chuck H]

Way back when I bought a box of Allen Bradley Ohmite pots, all sorts of values. Many had this locking feature, handy for bias adjustment. BUT none of them were values handy for amp biasing. Anybody need a 500 ohm locking pot, heavy duty mil spec? I got a box half full...

Is the shaft size inconsistent with other standard pots? I'm thinking you could just swap the mount and and collar nuts.

[Leo_Gnardo]

Is the shaft size inconsistent with other standard pots? I'm thinking you could just swap the mount and and collar nuts.

On the AB's the collar bushing is an integral part of the pot, so no swappage there. And ... swapping the resistor disc isn't an option either, like you can do on some standard pots like CTS.

[SoulFetish]

Way back when I bought a box of Allen Bradley Ohmite pots, all sorts of values. Many had this locking feature, handy for bias adjustment. BUT none of them were values handy for amp biasing. Anybody need a 500 ohm locking pot, heavy duty mil spec? I got a box half full...

Right! That's why I'm glad I found these. They fit right over standard pot bushings, can either be used with-or replace the standard nut.
Interestingly, I just serviced an old Matamp Orange lead 200. All 4 KT88 had their own bias control via externally adjustable panel mounted bias pots. Each pot was fitted with this kind of locking sleeve. I'm not sure why Matamp didn't just purchase 20k potentiometers manufactured with locking bushings... maybe they couldn't source them readily in England at the time?

[SoulFetish]

On the AB's the collar bushing is an integral part of the pot, so no swappage there. And ... swapping the resistor disc isn't an option either, like you can do on some standard pots like CTS.

Also, in case it wasn't clear in my post, these are fitted for pots that don't already have locking bushings on them. I'll shoot a pic of the other kind I use on my amp as well in a little bit.