Vintage Gibson Titan Medalist Amp Power Switch

[GT5283]

I have a vintage guitar amp that I needs the rotary power switch replaced. It is a SW78A. I believe it to be a 4 position, 4 pole switch. I have attached a pdf with a few pics and a schematic.
Gibson Titalist Rotary Switch.pdf
Can anyone tell me what a good replacement part would be? Thank you in advance for all your help!

[Chuck H]

It looks to me that this switch may have already been replaced or altered in function from the schematic. Then again, Gibson amp schematics are notoriously different from the actual amps so it's hard to be certain. Shown in the schematic is a four pole switch which should have at least ten leads connected. Your switch wouldn't appear to have ten leads connected.

I don't expect you'll find a suitable replacement for that switch. I think you'll need to change the arrangement to something more standardized. But you'll first need to know what that switch is actually doing in the amp in front of you and not just as per the schematic since they seem to be different.

Looking strictly at the schematic The A pole functions to engage the AC. The B pole is a polarity switch for a "death cap". This is strange since the amp appears to be earthed though there are some amps from the era that did this. No polarity cap or "death cap" type arrangement needs to be in this circuit so that pole could be eliminated. The C pole provides DC to the preamp circuit as a sort of "standby" function. There are other/better ways to do this though it would still require a rotary switch since it's clear there's only one control hole for this purpose on the amp. Another option would be to add a separate standby switch that functions differently in the circuit. This is what I would do even though it detriments originality and therefor collectability. I'd put it on the back of the amp to minimize cosmetic offense. Pole D controls the different pilot lamps that indicate if the amp is on and in play or standby mode. This function could be moved to the new standby switch. So now the standby switch would be a standby/indicator lamp control switch. They do make three and four pole toggles that can do this. So now you would have a power toggle and a standby/play toggle. And that's it.

I'm entirely unwilling to try and walk anyone trough all this modification unless you have confidence and experience working on electronic circuits and understand everything I've written above. Otherwise you should take the amp to qualified service individual to have the work done safely and correctly.

And there's still the matter of what that switch is actually doing in the amp now and how it may differ from the schematic. That would have to be known and navigated differently to do the work I've outlined.

[g1]

And there's still the matter of what that switch is actually doing in the amp now and how it may differ from the schematic. That would have to be known and navigated differently to do the work I've outlined.

The four power switch positions as labelled are off, standby, on, on. The second 'on' moves the AC 'death cap' to the opposite side of AC line.

[Chuck H]

The four power switch positions as labelled are off, standby, on, on. The second 'on' moves the AC 'death cap' to the opposite side of AC line.

Yep. I saw that pretty clearly. But there aren't enough leads connected to the switch in the photo for it to be accurate to the schematic. To be accurate to the schematic there would need to be ten leads connected to that switch. It's not clear in the photos but I count four.

[The Dude]

I like Chuck's idea of just using 2 switches and rewiring for a more standard power and standby configuration. That said, if you are dead set on keeping it original looking, I found this:

https://www.ebay.com/itm/18268439371...aX5YQ&LH_BIN=1

It is a 4 position 2 deck rotary switch. If you ignore the death cap switching, you only need a deck for power and a deck for standby. You should be able to make this work using your DVM to find switch contact positions that work for the application. You may need to jumper some of the pins together for it to work. If it doesn't work, you're only out 6 bucks.

[GT5283]

Thanks to all of you for your input.

I will take a closer look at Chuck's idea and the rotary switch that "The Dude" found on ebay.

Thanks again!

[Chuck H]

I like Chuck's idea of just using 2 switches and rewiring for a more standard power and standby configuration. That said, if you are dead set on keeping it original looking, I found this:

https://www.ebay.com/itm/18268439371...aX5YQ&LH_BIN=1

It is a 4 position 2 deck rotary switch. If you ignore the death cap switching, you only need a deck for power and a deck for standby. You should be able to make this work using your DVM to find switch contact positions that work for the application. You may need to jumper some of the pins together for it to work. If it doesn't work, you're only out 6 bucks.

I might be concerned with the actual specs for the switch. Current, voltage, make before break, etc. That's the only reason I didn't suggest a modern rotary switch. Though I have used similar switches to that one in HV circuits without issue and Ceriatone used them in high-ish current circuits (though they doubled the pole duty for that). In reality I doubt the original switch would be much better but it does look pretty burly for the AC mains switching deck.