Quote from: Tassieviking on April 18, 2023, 10:13:36 AMI would be 99% sure that the pots are standard 16mm with 5mm leg spacing...

You are correct. I replaced the factory pot with an Alpha 16mm diameter 5mm spaced 25k short pot and it fit perfectly, no issues. Purchased here: https://www.mojotone.com/25KB-16MM-Short-6-5mm-Split-Shaft-PC-Mount-Potentiometer

The push-pull pot was going to be a PITA to source from what I could tell. Too many spacing issues, 25k isn't common in a push-pull, etc. I just epoxied half of the shaft from the busted post I replaced above and now the knob fits fine, doesn't fall off when pulling it, cost $0, and a lot less effort overall. Sometimes the simple solutions are the best.



Thanks to everyone for entertaining my questions and poor ability to measure 4mm vs 5mm leg spacing with my cheap digital calipers.

My general review of these series-II amps are they're really nice. Very dynamic compared to some other solid state amps like a Peavey Bandit. Reverb that's nearly on par with Fender tube driven surfy reverb. Seemingly easy to work on with lots of space in the chassis.

For shoegazey tones I still prefer the Roland JC-120 as the tonal curve in that amp just has a really revealing top end that lets you hear all of the details in chorded passages even with fuzz. The Yamaha is a little darker and more obscured in that specific regard even when trying to tweak it with EQ. But otherwise, my ears generally prefer the Yahama, and it was vastly superior reverb than the dinky little tank the JC-120 has. My back definitely prefers the G50-112 and it's definitely more appropriate for bedroom use.

Good tip. On these amps the boards are mounted upside down in the chassis with all of the solder pads oriented upward.

QuoteI personally would remove the PCB and then mount it from the outside of the case by tightening all the pot nuts before soldering the new pots in, that way the pots are aligned before the solder locks them in position. You really want the pots tight against the panel before soldering, if you solder them first and then tighten up the pots you could put strain on the pots and solder joints.

Onto my next adventure.

QuoteI think it might be best if you remove the bad pots and clean the solder up with solder wick so you can get an accurate measurement of the hole spacing on the PCB.
I have not come across any 16mm or 5/8" pots with 4mm leg spacing before

Another alternative I thought of was to just purchase a panel mount pot with the correct shaft length and diameter so everything looks normal from the outside, rotate the pot 90 degrees, then run wire to the PCB.

That might have been what @Tassieviking was suggesting.

Some photos, including my attempt to measure using a cheap digital caliper.

As best I can tell the non-switched pots are approx 16.5mm in diameter with 4mm leg spacing.

Already ran them all through with DeOxit. The bass control pot has something crunchy inside in the first 1/3 of the travel and doesn't work quite right. The gain pot is missing 1/2 of the split shaft but is otherwise functional. Hmmm, might be less effort to epoxy on half a shaft from a sacrificial pot if I can find a match.

Will bust out the camera and my cheap digital micrometer and post the info soon.

Note that Yamaha was of no help, as expected.

QuoteYou are correct in that the parts for that amp are obsolete. We can only really reference parts to a specific model the are associated with, as we have so many models and part numbers. So, I'm not able to cross-reference  those parts to another amp, unfortunately.

I picked up a Yamaha G100 212ii and need to source a couple of replacement PCB mounted pots. The schematic has part numbers but I've come up empty trying to reference those. Does anyone know what the current production replacement units would be?

* Channel 1 bass potentiometer A25k for bass pot on PA2 (channel 1) #401000HS310760
* Channel 2 gain push/pull A25k with switch for gain pot for PULL FAT-B (channel 2) #401000HS310770