Gibson Super Medalist 4/10 Problems

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Gibson Super Medalist 4/10 Problems

Postby tomcurrie on Wed Sep 14, 2011 1:58 am

I picked up a Gibson Super Medalist recently. It was working fine until all of a sudden it started making this massive squeal/hum sound. When I power on the amp it sounds like crackling which I suspect would be dirty tube sockets or bad solder joint. When I plug a guitar into it is when I get the massive squeal/hum sounds. It's pretty deafening.

Any ideas of what my issue could be?
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Re: Gibson Super Medalist 4/10 Problems

Postby PeterS on Wed Sep 14, 2011 3:31 pm

Check the ground connection to the input jack...
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Re: Gibson Super Medalist 4/10 Problems

Postby tomcurrie on Wed Sep 14, 2011 10:13 pm

Turned the amp on today and plugged a guitar in. A little bit of crackling but no crazy noise/hum. Still no guitar signal coming through.

Any ideas?
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Re: Gibson Super Medalist 4/10 Problems

Postby PeterS on Wed Sep 14, 2011 11:23 pm

Wiggle the tubes in their sockets and listen...
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Re: Gibson Super Medalist 4/10 Problems

Postby tomcurrie on Thu Sep 15, 2011 12:47 pm

I wiggled the tubes. It didn't do anything.

I cleaned the tube sockets with contact cleaner. Still nothing.

When I first turn the amp on it makes a slight crackle for a few seconds then goes away.

When I plug a guitar into the amp, I get nothing.

There is a very very slight hum when the amp is on. Nothing unusual.

Any ideas?
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Re: Gibson Super Medalist 4/10 Problems

Postby PeterS on Thu Sep 15, 2011 1:38 pm

If you've got spare tubes try swapping them in (especially the preamp).

I dunno how comfortable you are poking around in there, if it was me I would open it up and try probing to see where the signal disappears --- with great care not to get electrocuted. If you have no test equipment take a length of wire (say a foot) and strip one end a bit, and tape up the other end. Try touching the bare bit to the grid connection of each stage of the amp in turn, as you work your way from the power stage towards the front end, at some stage doing that won't make a noise... you can find the schemo on the net...
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Re: Gibson Super Medalist 4/10 Problems

Postby tomcurrie on Thu Sep 15, 2011 7:20 pm

One of the power tubes tests extremely bad. The other tests really strong. I would figure you'd still get sound out of the amp with a bad power tube. It just wouldn't sound good.

you think a bad preamp tube could make it have no sound?
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Re: Gibson Super Medalist 4/10 Problems

Postby PeterS on Thu Sep 15, 2011 10:12 pm

I would figure you'd still get sound out of the amp with a bad power tube.


Yes you would.

A preamp tube with a blown filament (which you can see because the tube won't light up) would give you no sound at all, but that's a fairly rare failure, most 'bad tubes' just sound bad, not silent. At this point it's more likely you have a broken resistor or something of that sort, which you might find by visual inspection. However it would be a lot easier to troubleshoot with a voltmeter, and if you get one I can talk you through finding the fault with it.
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Re: Gibson Super Medalist 4/10 Problems

Postby tomcurrie on Fri Sep 16, 2011 3:23 am

All preamps tubes tested good.

I have my voltmeter.

Where should I start?
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Re: Gibson Super Medalist 4/10 Problems

Postby tomcurrie on Fri Sep 16, 2011 3:52 am

By the way, the guy I bought it from said it was working properly then all of a sudden it kind of freaked out and started making all that noise/hum.
And then he got no guitar output from it. There was no smoke or anything coming from a transformer. Nothing inside either chassis looks burned at all.
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Re: Gibson Super Medalist 4/10 Problems

Postby tomcurrie on Fri Sep 16, 2011 5:59 am

Also, I can't find a readable schematic for the Super Medalist 410. The power section runs 2-EL34/6CA7's and a 12AX7. The preamp section runs a 12AX7, 2-12AU7's and 3-6EU7's.
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Re: Gibson Super Medalist 4/10 Problems

Postby PeterS on Fri Sep 16, 2011 1:02 pm

The lack of a schematic is a nuisance but it's not a showstopper. The first thing to do is measure the cathode voltages of all the preamp tubes.

On the 12ax7 and 12au7 that is pins 3 and 8. For the 6eu7's that is pins 4 and 9.

Most of them will be in the ballpark of 2 volts, so measure them all, ignore the ones that are between say 1.5 and 3 volts, and report the rest here...

Does this amp have a transformer phase splitter? (How can I tell, you ask)... there's a power transformer and an output transformer and a choke (maybe) and a reverb driver transformer (maybe), if there's one more small one it's the phase splitter...
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Re: Gibson Super Medalist 4/10 Problems

Postby tomcurrie on Sat Sep 17, 2011 9:04 am

Got it working. Thank you PeterS for your help.
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Re: Gibson Super Medalist 4/10 Problems

Postby P-Dawg on Sat Sep 17, 2011 1:27 pm

tomcurrie wrote:Got it working. Thank you PeterS for your help.


And the fix was???

Inquiring minds want to know.
If you believe in coincidence, you're not looking close enough-Joe Leaphorn
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