bias pot for Ampeg SVT-3 pro.. need recomendation

[Bishop]

Can someone recommend me a good bias pot replacement for the Ampeg SVT-3 pro? I have one that loses bias over time and I'm fairly sure that 10K trimmer pot is the culprit. I'd like to know if anyone has had luck with something specific.

Bonus points for something available from Mouser.

Thanks!

[MarkusBass]

http://www2.mouser.com/ProductDetail...cLxTM7CafZ0%3d

I always secure the trimmer with a drop of a nail lacquer. The trimmer changes its resistance due to vibrations of the amp.

EDIT: I've just noticed that they do not have it available. It's funny because in Poland I can buy it without any problems . Check similar trimmers.

Mark

[Bishop]

http://www2.mouser.com/ProductDetail...cLxTM7CafZ0%3d

I always secure the trimmer with a drop of a nail lacquer. The trimmer changes its resistance due to vibrations of the amp.

EDIT: I've just noticed that they do not have it available. It's funny because in Poland I can buy it without any problems . Check similar trimmers.

Mark

Thanks, I'll probably end up getting whatever will fit and do the nail polish thing. It seems like over the years people have recommended "precision" pots or stuff like that, so I was wondering if anyone had actually done that with something specific.

[MarkusBass]

The trimmers that I mentioned previously will be available at Mouser on 13th October (within a week).
I fixed a lot of SVT3Pro and never heard, used, or seen precision pot as a bias pot in the amp. It's sufficient if you secure the trimmer with nail lacquer.

Mark

[Enzo]

Do you have actual evidence the trimmer is shifting, or just a feeling? Part age, parts change with heat. Mains voltage changes.

I think most of the 10-turn pots in bias circuits are in tube amps. And I think it silly myself. In my years doing service, I can;t think of many times I had bad bias pots, other than whole-amp meltdowns with burnt up the trimmer along with the transistor it controls and a lot more. if your trimmer is defective, most any trimmer would work.

Frankly, at least during service, I want a trim pot I can adjust quickly. if my circuit is overheating, I don't want to have to fiddle with a 10-turn for a while to get it down to the range I want.

[Bishop]

Do you have actual evidence the trimmer is shifting, or just a feeling? Part age, parts change with heat. Mains voltage changes.

I think most of the 10-turn pots in bias circuits are in tube amps. And I think it silly myself. In my years doing service, I can;t think of many times I had bad bias pots, other than whole-amp meltdowns with burnt up the trimmer along with the transistor it controls and a lot more. if your trimmer is defective, most any trimmer would work.

Frankly, at least during service, I want a trim pot I can adjust quickly. if my circuit is overheating, I don't want to have to fiddle with a 10-turn for a while to get it down to the range I want.

Point taken.

It was more than a feeling really, the bias would shift as the I pressed the pot with a chopstick. I just removed the pot and confirmed that it's values changes (sometimes fully opening) out of circuit with minor amounts of pressure.

[Enzo]

OK, fair enough. But know that pushing on a pot can splay the contacts a little and that alone will alter its value. it is hard to test a pot with an ohm meter, other than gross measurements. What I like to do is first use clip wires for a steady connections, but the test itself I use audio. I put the pot in series with an audio signal and listen through an amp. As I turn the control, I don;t really expect much change of volume, but any interruption of wiper contact will be instantly heard. I believe your pot is defective, so for the price of a new one, get a few.