trim pots

[scole]

are these the ones i should use?
http://www.vishay.com/docs/57027/63.pdf

[TheTinMan]

What's the application? PCB? Eyelets? Turrets? And what are you trimming?

IOW if you want a bias trimpot that's accessible without taking out the chassis, the choices are completely different from a trimpot that you want to add to a Blues Jr. PCB.

Chip

[tubeswell]

Yep you could use those ones for bias adjustment. I used even more basic ones on my recent 5G9 build.

http://www.jaycar.co.nz/productResults.asp?FORM=CAT

[stokes]

For a bias adjust pot the cerment type is a better choice.Most standard volume type pots dont take dc very well.With a bias pot you set it and leave it like that for a long time.The dc current,although very low,can eventually burn the trace where the wiper sits.

[tubeswell]

Wow! - I thought trim pots was just trim pots and any one (of the correct resistance range) would do for bias. I thought they were all designed to be permanently set

[stokes]

Wow! - I thought trim pots was just trim pots and any one (of the correct resistance range) would do for bias. I thought they were all designed to be permanently set

I'm talking about a standard volume type pot.Some people use a volume pot for a bias adjust and some years later they need replacing.You know how a volume pot gets scratchy if a cap leaks dc into it?If it is left like that,it will eventually burn the trace,the problem is compounded with a bias adjust since the wiper sits in one place and slowly burns the trace in that spot.

[anson]

I wouldn't recommend using that pot for the adjusting of the balance of filament leads. The "hum-dinger" pot, I mean. That data sheet doesn't specify the power rating of the trim-pot, but I'm guessing it's not as much as you'd need for the hum-dinger trim-pots.

For the hum-dinger trim pots you'll need a 1 W trim pot if it's 200 ohm, and 2 W if it's 100 ohm. I've toasted weaker trim-pots that were rated at 1/4 watt when I used them as hum-dinger trim-pots, because I didn't know any better.
hope this helps, Anson

[anson]

Actually those values are probably a bit overkill. Sorry. But I promise you, I toasted a .25 watt trimpot when I used it as a hum dinger! It took about six months for it to happen though... Anson

[stokes]

1/2 watt pots are common for hum balance.For the record,1/4 watt anything has no business anywhere in a tube amp.