Trim pots

[calman46]

How critical is to used the factory values on the trim pots for DC offset and idle current ? Like subbing a 2k for the original 2.2k on bias and a 1k for the 680 on DC offset . I have recapped some Mitsubishi DA A10DC amps and would like to put in so sealed trimpots. Mouser an Digi Key have a limited selection now. As a general rule can you go to the next value ? either up or down in value ? I have one more question , if wiper contact is lost does the circuit " see " the trim pot value ? Thanks

 

[dlucy]

Going up or down is fine... you're just losing a little adjustment.

If you put in a 2.2k for a 2k, that will work fine and you'll just lose a little finesse in values as the turn you make covers 10% more value than before. No problem. This would be my choice.

If you go down, say 500 ohm for an original 680 ohm, then you'll lose all the values between 501 and 680 ohms... so you may not be able to dial in as well. But it will still fundamentally "work".

If you go slightly UP in value and switch from a single turn trim pot to a multi trim trim pot, then you regain all the finesse... and have all of the original range... plus some.

 

[jhjove]

I have one more question , if wiper contact is lost does the circuit " see " the trim pot value ? Thanks

If the pot is used as a voltage divider "tap"; lug 1 is the input, lug 2 (wiper) is the output and lug 3 is circuit ground.
From the wiper lug circuit POV, if lifted, it's an open circuit.

If the pot is used as a variable resistor, (you short lug 2 to lug 3) then with the wiper failing you'd have the complete trim pot value. I've seen most of the DC offset and idle current pots done this way.