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Old 28th March 2009, 02:18 AM   #1
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Default Advice on trimpots.

I plan to use trimpots in two locations in a new amplifier build, and I'm going to leave them in so I can make adjustments as various circuit parts age. Given that they are to be "permanent," should I go for the $17.00 a piece Bourns cermets or is there a better and less expensive choice, both for durability and performance? I'll be using one 500 ohm 25 turn pot and one 1K ohm 25 turn pot. If anyone has had a lot of experience with trimmers either as a diyer or a pro, and has come to favor one brand and model over another, please let me know.

And just for curiosity's sake, what makes a trimmer worth $17.00 or more?

Thanks.

George
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Old 28th March 2009, 02:26 AM   #2
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Well, when you're spending that much for a trimpot it may be sealed and spec'd for avionics (fire-resistant) purposes.

Take a look at 3266 and 3296 from Bourns. There are less expensive versions at Jameco -- which are of a different make. I use both.

You can also set up the circuit for "clip and trim".
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Old 28th March 2009, 09:53 AM   #3
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You might also want to look into the bulk metal foil trimmers that Vishay makes. I use the cheap cermet types from digikey but I mostly only use them until I find the value I like and then swap in a resistor. If I were going to leave one in by design I'd certainly investigate the foil. The only place I've seen them for sale is Michael Percy. ($9.50 IIRC) and I don't know if he still sells them.
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Old 28th March 2009, 06:55 PM   #4
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Default Re: Advice on trimpots.

Quote:
Originally posted by Colescuttle
I plan to use trimpots in two locations in a new amplifier build, and I'm going to leave them in so I can make adjustments as various circuit parts age. Given that they are to be "permanent," should I go for the $17.00 a piece Bourns cermets or is there a better and less expensive choice, both for durability and performance? I'll be using one 500 ohm 25 turn pot and one 1K ohm 25 turn pot. If anyone has had a lot of experience with trimmers either as a diyer or a pro, and has come to favor one brand and model over another, please let me know.

And just for curiosity's sake, what makes a trimmer worth $17.00 or more?

Thanks.

George
I've got some Bourns 500 ohm and 200 ohm trimpots sitting around that I no longer have any use for.
Yours for the cost of postage.
Let me know....
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Old 28th March 2009, 11:13 PM   #5
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If any are for bias, I suggest wirewounds. It takes serious abuse before their wiper lifts.

Cheers!
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Old 29th March 2009, 04:31 PM   #6
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Default Re: Re: Advice on trimpots.

Quote:
Originally posted by MCampbell


I've got some Bourns 500 ohm and 200 ohm trimpots sitting around that I no longer have any use for.
Yours for the cost of postage.
Let me know....

Thanks for the offer Matt, but I think I will go for wirewound pots as suggested by Gregg. Even if it's overkill, it'll give me some peace of mind since I'll be running these amps in overbiased class A, and one of the pots will be used to adjust AC current gain.

George

Thanks, everyone for the advice.
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Old 29th March 2009, 05:37 PM   #7
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Default Re: Re: Re: Advice on trimpots.

Quote:
Originally posted by Colescuttle



Thanks for the offer Matt, but I think I will go for wirewound pots as suggested by Gregg. Even if it's overkill, it'll give me some peace of mind since I'll be running these amps in overbiased class A, and one of the pots will be used to adjust AC current gain.

George

Thanks, everyone for the advice.

No problem! To be honest, it sounds like a smart move!
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