installing a volume pot

[Hurricane Bob]

can I use a Fender Squire tone pot for my Ampeg G-18 volume pot? The squire pot is 500k. Got it all apart and ready to solder--

[Dru Edwards]

What's the pot value on the Amp? Some amps use 1M so you want to make sure you keep the same value.

Also, your Squire tone pot is probably Linear but your amp's volume (and guitar volume as well) is most likely audio tapered. I'm guessing it won't be a good match. If you're all set to solder no reason not to try.

[Hurricane Bob]

It worked! the old pot was 50K and the new one is 500K, hope I don't blow anything. This old Ampeg G-18 has some mojo for a transistor amp, thanks everyone

[MC5C]

You won't hurt anything with that modification. You will reduce the current flowing to the second pre-amp stage, but it's a voltage amp, not a current amp, so no harm as long as it has enough current to work. You may change the way the tone controls sound a bit. If you put in an audio taper pot where a linear taper was, or vice versa, the sensitivity of the volume control will change, it may get more abrupt, all the change at one end or the other. If it's working and you are happy, I would call it good.

[Hurricane Bob]

What are these Ampeg G18 amps worth? Its in mint shape and hardly used. I would consider selling it to fund a Bugera V22

[Dru Edwards]

Hi Bob, did you notice any tonal differences with the volume pot change? Perhaps changing the volume from 0-2 is different than it used to be? Or that it's brighter than before? Those are the differences I would expect on an electric guitar what that pot change.

[jonfields45]

I recently bought a 50K linear POT at Radio Shack. I had to saw the shaft to the right length. On-line no problem. I would go get the right value (and taper would be nice too, an "A" marking on the pot means it is analog, "B" is linear). 10x is a pretty large change for a tone stack component.

[MC5C]

When I looked at the schematic the volume pot is just a voltage divider function coming out of the treble pot of the tone stack. The value change isn't going to change the voltage divider function at all, although if the taper is different it will react to change differently. The schematic I found didn't call out the taper. Since this is a solid state amp I kind of assumed the input impedance to the next pre-amp stage was somewhat high so I didn't think going to a 500K pot would make much difference, although I didn't do the math.

The tone change you see in a guitar circuit is more down to interaction with the reactance of the pickup coil to create a low pass filter, I always thought, although again I have never done the math.

Some people seem to love those G18 Ampegs.

[Hurricane Bob]

Seems like the tone didn't change at all, the volume pot works as it should at all volumes. Thanks for all the input fellas, its a cool amp but I am a tube amp lover. If anyone is interested I am willing to sell it for $150.00 or so.

[Dru Edwards]

Glad to hear it worked out well, Bob. Knowing how to solder comes in handy for guitarists.