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Old 5th February 2012, 03:22 AM   #1
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Default Old guitar amp question

Hi,
I've recently come into possession of an old '65 Supro 16T guitar amp. It's completely original and I tried it briefly to see if it still worked. It powers up fine and plays well but has a slight background hum. I see it has an old Mallory FP capacitor in the power supply. Am I courting disaster powering this thing up? I haven't turned it on since I noticed the hum.

Edit: I can't find a Supro schematic but it's apparently the same as this Gretsch.

Last edited by rntlee; 5th February 2012 at 03:25 AM.
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Old 5th February 2012, 03:34 AM   #2
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yes you are courting disaster. Old amps have a predilection for exploding their electrolytic caps with messy, smelly and destructive results.

Do a quick search in here on resurrecting old amps - there are plenty of threads on the subject
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Old 5th February 2012, 12:12 PM   #3
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Just one other question,
I can't find the correct value 3 section FP cap (450v 20-10-10), is it ok to use a 525v 20-20-20 in it's place?
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Old 5th February 2012, 12:43 PM   #4
eyoung is offline eyoung  United States
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you could try it or just use individual caps , don't forget the cap on the 12ax7...

Elwood
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Old 5th February 2012, 12:48 PM   #5
GloBug is offline GloBug  Canada
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Generally you can go up in voltage.
You should be careful raising the capacitance.

In this particular case you are OK. The 20uf in the Gretsch schematic is the first filter cap after the 5Y3 rectifier. You don't really want to raise this much, if at all, it will stress the 5Y3.

The other two should be OK to go from 10uf to 20uf.

You don't have to by a "Can cap" you can buy single smaller capacitors and install them inside the chassis.
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Old 5th February 2012, 12:49 PM   #6
GloBug is offline GloBug  Canada
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Quote:
Originally Posted by eyoung View Post
you could try it or just use individual caps , don't forget the cap on the 12ax7...

Elwood
What cap?
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Old 5th February 2012, 01:36 PM   #7
BB62 is offline BB62  United States
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If that cap physically fits it should be OK. The preamp and tremolo are both cathode biased. If anything it should have a little less AC line hum than the original circuit. Be careful in there.
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Old 5th February 2012, 05:55 PM   #8
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Thanks for the help, guys. I was thinking that an FP cap would be more "original"...though I guess I could leave the old one mounted anyway. It's a kinda desirable amp...the last one on ebay went for $700.
This is the interior: http://i247.photobucket.com/albums/g...e/CIMG4850.jpg
Would I also need to replace the black and the orange cap? Not all the ceramics too I hope?
Sorry about all the dumb q's.
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Old 5th February 2012, 05:59 PM   #9
GloBug is offline GloBug  Canada
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Yes give that orange and the black one a swap too, it also appears to be electrolytic.

Yes for resale value, keep the the old cap and tack the new caps underneath, or "restuff" the cap with three smaller ones.

The ceramics should be OK
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Old 6th February 2012, 08:49 AM   #10
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Leave the ceramics alone, they are the soul of your tone!
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