Sears silvertone 1481 - Shocking sound!

[Rubbersalt]

Couple of days ago, I was playing my silvertone, everything was fine. Took it home, then brought it back to my buddy's house yesterday to play it again. Plugged it in, it shocked the crap out of me. It was turned off when it shocked me. It felt like 110, but I couldn't find anything inside that was grounding out. I got shocked through the tip of the on/off switch and the guitar cable - the sides of the plug, not the tip.


I've got it apart, the caps should be discharged at this point(shorted them out). The fuse is fine, but i don't really see any type of ground circuit.

My question is, how do I add a ground cable? Do I just directly ground it to the chassis?

[Wittgenstein]

You will need to replace the 2 prong power cable with a 3 prong cable, attaching the ground to the chassis (a dedicated bolt with lock washers). Also make sure to remove the death cap. This still might not make your amp 100% safe depending on how they run the mains. The safest thing to do would be to also add a 1:1 line isolation transformer if there is no power transformer. Here is some more reading below.

http://music-electronics-forum.com/t16486/
Silvertone Model 1430 Amp Modification
http://music-electronics-forum.com/t17440/

[52 Bill]

The schematic that I found shows that this amp has a power transformer, so adding an isolation transformer is unfounded here. Changing the ac cord to a three wire one and rewiring the ac section will fix this.

Were you standing on a concrete floor in bare feet?

[Rubbersalt]

Nope, I had my boots on. I sat on a bed - still shocked.

I'm trying to locate the "death cap" to remove it, I have a good power cable with a ground.

Edit; think i found it. Goes from the fuse to the chassis. There is a 0.05 cap rated at 600volt. There is also 2 68k ohm resistors, both go to the 6x4 tube, not in parallel

[Wittgenstein]

Nope, I had my boots on. I sat on a bed - still shocked.

I'm trying to locate the "death cap" to remove it, I have a good power cable with a ground.

As you can see in the schematic here, it is the .05uf cap with one end attached to mains and the other soldered to chassis. Just make sure that the fuse is hooked up to the hot side of the mains, and not the neutral.

[Rubbersalt]

Basicaly, i just to make sure I'm doing this right.

I remove the old 2 prong wire, i remove the cap going from the fuse to the chassis.

I reconnect my new cable, the hot wire goign to the fuse, the nutural going to the switch(where current 2 prong is) and the ground connects to the chassis.

Right?

[Rubbersalt]

Looking at my new - well used power cable chopped off something i forget the name of, i noticed the color code may be off. Just for clarifications, the small slot(right) in an outlet is hot, while the big slot is neutral(left) and the round hole(bottom) is ground?

The cable I have is colored like so. Small prong=white, big prong=black, and the ground is green.


Tested with my multi meter

[Rubbersalt]

Good morning everyone.


bump!

[Wittgenstein]

Looking at my new - well used power cable chopped off something i forget the name of, i noticed the color code may be off. Just for clarifications, the small slot(right) in an outlet is hot, while the big slot is neutral(left) and the round hole(bottom) is ground?

The cable I have is colored like so. Small prong=white, big prong=black, and the ground is green.
Tested with my multi meter

When looking at the 3 prong cable with the plugs facing you, the bottom is ground, top left is neutral, and top right is hot.

For old polarized 2 prong cables, the small terminal is hot, the bigger terminal is neutral.

[sgelectric]

Rubbersalt,

When you wire the new cable into the chassis it should be as follows:

Black wire(hot) to fuse tip>fuse sleeve to switch>switch to transformer primary
White wire(neutral) to other transformer primary lead
Green wire(ground) bolts to chassis

The transformer primary leads are often black
Do not switch the neutral wire as you proposed in an earlier post.

SG

[Rubbersalt]

Thanks guys, this is exactly what i needed to know. Ill get it fixed up tonight and report back if i get shocked or not !

[Wittgenstein]

Thanks guys, this is exactly what i needed to know. Ill get it fixed up tonight and report back if i get shocked or not !

Just make sure that the amp is unplugged and the electrolytic caps are discharged when working on your amp. You can make a simple discharge tool in no time. No since trying to fix your amp and shocking yourself in the process.

[RWood]

Btw, those 68Ω resistors are the artificial center tap to ground for the filament circuit.

[jmaf]

Thanks guys, this is exactly what i needed to know. Ill get it fixed up tonight and report back if i get shocked or not !

Before you switch it on, with the amp plugged in, take your multimeter on the AC volts scale, one probe to the chassis, hold the other with your right hand and read the voltage. If you read a voltage, it's not good. And if you see anything above 50 to 70 volts it's awful wrong and it'll shock you - no need to test it the painful way.

[Rubbersalt]

Well, I tested it with the multimeter. Turned off, 1 end of my multimeter and other on the chassis ground.

I get a voltage reading of 40volts AC.

Is this good or bad? Will i get shocked?