Doing a 3-prong mains cable upgrade on an old amp

irishstu

irishstu

really experienced
Hi all,

I'm doing a bit of work on an old Silvertone 1481 amp (torn speaker, missing back cover). However, I've advised the owner that first and foremost it would be wise to upgrade the old 2-prong cable to a 3-prong one.

The schematic is available here: http://www.prowessamplifiers.com/schematics/silvertone/Silvertone_1481.html

Anyway, I've drawn out the wiring from the wall to the transformer (as shown on that schematic) and also what I believe the mod would be. Can anyone comment on if I've got this right? Thanks.

silvertone-mod.jpeg
 
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Here you go. The only thing that I could see different is the placement of the fuse.

These schematics are the input AC section to a 5E3 amp but applies basicially to all conversions. Mainly - get rid of the Death Cap!

Wiring Diagram.jpg
 
Yep, new diagram is correct in both cases. The issue with the "death cap" is that if it ever shorts across, it lights up the whole chassis.
 
I had a tech replace the 2 prong plug on my 63 Princeton. Everytime I sang and touched a mic I'd get a nasty shock. In fact if I was in my bare feet on a cement floor and touched the guitar, I'd feel that electricity flowing.
 
Cool, thanks. Is getting rid of the death cap going to end up giving me more hum? If so, is there a workaround for that?

By the way, the amp currently (excuse the pun) works fine if I plug the plug in in one direction, but I get a pretty uncomfortable shock if it's plugged in the other way if I touch the amp chassis or even the guitar (I realise this is pretty common for these old amps - crazy).
 
irishstu said:
Cool, thanks. Is getting rid of the death cap going to end up giving me more hum? If so, is there a workaround for that?

By the way, the amp currently (excuse the pun) works fine if I plug the plug in in one direction, but I get a pretty uncomfortable shock if it's plugged in the other way if I touch the amp chassis or even the guitar (I realise this is pretty common for these old amps - crazy).
Click to expand...
If it does, there's a thing you can do, I've done it, with just a resistor, maybe a cap also and some wire. Can't remember what it's called, at the moment. Raising the center tap bias on the tube heater supply, or something.

I have CRSA disease.

Can't Remember Shit, Anymore,

If that wanes, as it does, sporadically, I'll let you know. Meanwhile, Google is God.
 
BoomBoomBigelow said:
A universally acceptable, even mandatory, mod to a vintage amp, but some folks save the old parts for the corksniffers.
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Sniff sniff. Zee bookay! The tech gave me back my cord and death cap. I am keeping them just in case I ever sell mine to such a person.
 
OK, all done. Everything appears to be working fine. Thanks again for the help everyone.

Before:
Silvertone-0.JPG



After:
silvertone-1.JPG


silvertone-2.JPG


silvertone-3.JPG
 
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