Gibson G50 hums...

[matthewdfisher]

Hey, everyone, just picked up a Gibson G50 SS amp and it's got a hum. I can also hear the tremolo circuit "pulsing" in the hum, even when the effect is not engaged. Would replacing the big can capacitors be a good place to start? If so, here's a picture of the bottom of one of them, and I can't seem to find a direct replacement. It's a 2000uf 35V cap:

Probably dumb questions, but which lug is positive and which is negative, and what might be an acceptable replacement? Thanks in advance!

[Leo_Gnardo]

Yes replacing the filter caps would be first order. Not a dumb thing to ask which end's which, because most can caps are can negative, terminals positive BUT rarely you find one that's reverse built. Two things real quick, you probably won't find can caps in your needed values, just as well, they'd be very expensive figure $40 each. Replace 'em with individual caps of similar ratings. To double check your can caps' polarity clip voltmeter leads, one onto ground, the other on the the cap's terminal. You'll probably see a positive voltage, 30V or so, then you know which end's which when you solder in replacements.

The pulsing will likely disappear once you have working power supply caps in place.

One cap that looks like a filter cap is probably used for DC blocking on the audio output. You'll want to replace that one too, and make sure its polarity is correct.

And a hearty "welcome aboard!" You aren't by chance Matthew Fisher from Procol Harum? I'll bet you get asked all the time.

[matthewdfisher]

Thanks for the response, Leo, that's pointed me in the right direction. What do you mean by individual caps, though? Do you mean the much smaller axial type? (I'm not a 100% rookie, I just don't want to blow anything up or start a fire)

I am, unfortunately, not the Matthew Fisher from Procol Harum, although I was certainly aware of him. Same name, way different talent...

[g1]

Modern equivalent and more common would be 2200uF, to make room for the higher wall voltage we have today, you may want to go with higher than 35V, 50V should be common.
For the blue cap in your picture, the 4 lugs around the outside that connect to the casing are negative, the inner lug is positive.
But you are not likely to find a can that mounts the same way, unless you want to spend a lot. The modern equivalent will be much smaller, like this: http://www.digikey.com/product-detai...5187-ND/245046
You will want to mount it in the chassis, disconnect the old and leave it in place for looks, then connect your wires to the new one you mounted inside. The new one will have the negative lead marked.

[52 Bill]

There are two twist-lok caps in you photo, one silver color (partially hidden) and one with a blue sleeve. The blue sleeve may be used as an insulator to keep the case from grounding to the chassis. So that one might actually be for the negative supply voltage. You need to check into this.

Every can type cap made back in those days was stamped with the value and with information as to what terminal was what value and what was positive and what was negative. Some would be stamped something like "can is negative". Inspect the caps and find out how they are marked and you will be able to replace them with modern equivalents.

[matthewdfisher]

Thanks for the replies! Nice to think I might get this thing running better for only a couple of bucks.

[g1]

Schematic is attached. There are two 500uf 25V caps and two 50uf 16V caps that should probably be replaced while you're at it. You can use 470uf 35V and 47uf 16V.

[g1]

As you mentioned tremolo, it may be this schematic instead. In that case it wouldn't have the 50uf16V caps.