Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: shaun on May 28, 2020, 12:41:47 pm
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Heyo,
I'm rebuilding an old stereo amp with a dual gang volume pot that incorporates an on/off switch as a push-pull knob. Very hard to find a replacement. Tubesandmore has this:
https://www.tubesandmore.com/products/potentiometer-bourns-audio-solid-shaft-dual-mini-push-pull
But it's rated at a mere 0.1 watts, designed for guitar installation. As it's the nearest thing I've found, I wondered if anyone knew whether a 0.1w rating would suffice in a stereo amp. Of course, I'm open to suggestions.
Thanks for any help.
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Any pot will work.
There is no DC voltage on amps pots.
This one is ok
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Thank you Latole!
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If the switch is for the AC voltage coming in from the wall, I don't think that it will work. While it's true that there is no voltage on the resistive elements of the pot, there is AC voltage on the switch. The Amp/Volt rating of the switch is of concern. The switch should be rated for something like 6 amps at 125 volts AC or 3 amps at 250 volts AC.
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It is not just the DC. The AC voltage, squared, divided by resistance, is audio Watts in the pot.
You managed to give _NO_ actual conditions.
Ass-ume audio signal is 1 Volts average (may be 5V speech/music peaks). And ass-ume pot is 100k. 1^2/100,000 is 0.000,010 Watts.
A 0.1W pot appears to be much bigger than required.
OTOH, the OUTput of a large PA amp may be 70 Volts Audio. Put that on a 20 Ohm pot (once used for car radio faders) it is 250 Watts on a 5W-rated pot. Smokin!
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If the switch is for the AC voltage coming in from the wall, I don't think that it will work. While it's true that there is no voltage on the resistive elements of the pot, there is AC voltage on the switch. The Amp/Volt rating of the switch is of concern. The switch should be rated for something like 6 amps at 125 volts AC or 3 amps at 250 volts AC.
Ah yes, thanks. That rating is usually easy to find, but the amp rating is not printed on the switch itself, unlike some. This from their spec sheet, but no mention of the switch rating:
Power Rating
Linear......... 0.2 watt
Audio ........0.1 watt
Maximum Operating Voltage
Linear ........200 V
Audio .........150 V
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It is not just the DC. The AC voltage, squared, divided by resistance, is audio Watts in the pot.
You managed to give _NO_ actual conditions.
Ass-ume audio signal is 1 Volts average (may be 5V speech/music peaks). And ass-ume pot is 100k. 1^2/100,000 is 0.000,010 Watts.
A 0.1W pot appears to be much bigger than required.
OTOH, the OUTput of a large PA amp may be 70 Volts Audio. Put that on a 20 Ohm pot (once used for car radio faders) it is 250 Watts on a 5W-rated pot. Smokin!
Thank you PRR. It seems I ass-umed too much. Or, being from NZ, I arse-umed to much. I appreciate the math explanation and hopefully will not need to ask that question ever again:).
The amp is an old stereo I'm trying to rebuild, 2* SE 6V6's. Probably 4-6watts output per side, maybe, and very low level input from a modern turntable, straight into the volume pot.
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Are you committed to keep the switch attached to the volume control? If you were to separate the On/Off switch from the volume control, there would be more options available. If this is collectible vintage hifi gear ($$$$), I can understand the desire to keep it as original as possible, otherwise not so much.
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Are you committed to keep the switch attached to the volume control? If you were to separate the On/Off switch from the volume control, there would be more options available. If this is collectible vintage hifi gear ($$$$), I can understand the desire to keep it as original as possible, otherwise not so much.
Yep, it's an old RCA console, so I'm trying to keep it looking original.