#1
So I got a pretty good, big, loud solid state amp from the 70s' recently for about $25. The reason it was $25? It's got all sorts of electronic quirks. Most of them i've fixed, but the one thing i'm not sure about is the power cord. It's two-pronged, not grounded, and given that it's duct-taped together where it goes into the amp it looks like someone replaced the original power cord with it. Coincidentally, the amp also appears to have grounding issues. It's given me a tingle a couple times, and there's one particular guitar I have (an old used bass) that will make it hum if your fingers aren't touching the strings or a knob.

The conclusion i've come to is that the power cord needs to be replaced with a grounded plug, but I don't really know a lot about electronics, so I have no idea if i'm right. Would a non-grounded plug cause the issues i've seen, or should I look inside the amp for other causes? And where would I even get a replacement plug/cord?

While I'm here, I've heard that the solder connections in solidstate amps will generally break after a while just from the vibration of the speakers, and will need to be repaired. Is there an easy way to tell if a solder connection is broken or not?

(As a sidenote, the original owner was selling it was because "it only turned on half the time." Reason? The plug is still polarized, but the prongs have no indication of which is which, so half the time he would plug it in the wrong way. Three seconds with a sharpie and it turns on all the time. )

Thanks
#3
The chassis not being grounded can give you a tingle on old school amps w 2 prong plugs. I replaced the one in an old ampeg I had. Is the current one even polarized, one blade is bigger than the other? The ground or green wire I attached to a screw on the chassis.
#4
What I find odd is that it only works with the plug in one way. it should work with it inserted either way. One way would make the chassis hot and plugging it in the other way would make it neutral.
#5
Quote by Tackleberry
The chassis not being grounded can give you a tingle on old school amps w 2 prong plugs. I replaced the one in an old ampeg I had. Is the current one even polarized, one blade is bigger than the other? The ground or green wire I attached to a screw on the chassis.


No, the current plug isn't even polarized. Looks like this quick google image search result: http://www.washington.edu/computing/global/plug_c.png Only even more old-looking and with flat blades. So are you saying I need to replace the plug and attach the ground wire to the chassis?

And yeah, if it's not plugged in the right way it doesn't even turn on, at least the five or six times I've tried it. I figured house current is polarized and the power supply could only accept it one way? I guess? The amp is a Randall Commander II btw, if that means anything.

Still don't know where to buy plugs :/ I'll try radioshack, I guess.
#6
Not sure how you even plug the cord pictured into an american wall socket. No a plug like that wont be polarized. So yea it could be plugged in backwards. But another issue is if it has a foreign plug on the cord then its probably set up for a different voltage anyways. The one pictured is 16a/250v.

My 60s era ampeg I went to home depot/lowes and bought a 3 prong power cord. But it was still an american amp set up to run on 110v AC. So it wont be that simple for your amp Im afraid to just swap cords. It may need a new transformer.
#7
Sorry, that was probably a bad choice of image. The plug definitely fits in an my american wall sockets, it's just not polarized. I'll take a look at the power supply and see if i there's anything written on it.
#8
My ampeg had the same nonpolarized plug. Not knowing much it took me a while to figure out plugged in one way touching the amp to change settings would give you a tingle, other way it was fine. The chassis is connected to ground internally. A polarized and grounded modern power cord fixed the problem.