Question for the electric guru's out there.

[Fordman]

Hello All,

I aquired a 1965 Magnavox Astro Sonic Console that works and looks great. I want to make a touchscreen jukebox out of it, on the side where the records are usualy stored. I found some extra RCA plugs to plug in a tape recorder or anything else. I used my mp3 player to plug in, switched the knob to AUX and it played great. But, when I picked up the mp3 player, I could feel electrical current running through it. A neighbor says its because the stereo isnt grounded.

Question is: How would I make it a grounded unit? I'm no electrician but I can probably do it with clear explanation. From reading on the net, it has an old tube amp. Are tube amps able to be grounded? I dont want to shove a computer in there and a touchscreen for it to go 'Zap, Crackle' Pop' because there is some eletrical current flowing through the RCA to 3.5 mini plug cable into the back of the computer's sound card.

Any thoughts?

Thanks,

Fordman

[orion]

If you can get to the insides of the RCA jacks themselves you can solder a ground wire to the sleeve connector of the RCA jack (the negative lead...usually the black wire) and run that to a ground. If you don't want to go that route and if you aren't afraid to spend a little money for a much simpler solution you could go with a direct box like this one http://www.whirlwindusa.com/dirbox.html#pcdi and some XLR to RCA adaptors. Basically a direct box is just a fancy transformer that you would run between the mp3 player/pc and the amp.

[Ed_McCarron]

Don't ground it.  Is it a tube amp?  Its probably designed that way.

Try one of these:

http://www.radioshack.com/product/index.jsp?productId=2062214&tab=summary

It breaks the electrical link between the two devices.

[orion]

Don't ground it.  Is it a tube amp?  Its probably designed that way.

Try one of these:

http://www.radioshack.com/product/index.jsp?productId=2062214&tab=summary

It breaks the electrical link between the two devices.

I have never had much luck with that product from radio shack, in every application that I have ever tired to use it, I always still had a hum.. and that's the reason why I recommend the whirlwind. Those things just work. Of course if there is no hum, it might just do the trick. Worth a shot, I'd say, good call.

[richms]

If you are feeling a leakage current then it should be tripping out your RCD or whatever you call them there...

Without knowing how it is currently wired its hard to say how to sort it out - chances are it has a 2 pin mains cable, but some old stuff actually did have a live chassis with things exposed to the user.

if thats the case then an isolating transformer is in order. If it has a proper power supply then it could be leakage thru some capacitors to the incoming power to remove noise, so removing them and fitting a proper power noise supressor and a ground would do.

Whatever, dont just ground the RCA's or connect to something that is grounded since if it is a live chasiss then you will blow stuff up.

[digitaldj]

Try rotating the A/C plug and give that a try. It may just be all about polarity like the new A/C line cords.

[Ken Layton]

Look to see if the unit uses a power transformer to run the tubes. Chances are it does not and is a "hot chassis" design so popular back then.

Don't even attempt to ground a hot chassis amplifier and be very very careful about what you hook up to the amplifier. You can literally destroy something in the blink of an eye not to mention zap the hell out of you.

[orion]

Look to see if the unit uses a power transformer to run the tubes. Chances are it does not and is a "hot chassis" design so popular back then.

Don't even attempt to ground a hot chassis amplifier and be very very careful about what you hook up to the amplifier. You can literally destroy something in the blink of an eye not to mention zap the hell out of you.

"Hot chassis" Why does every product from the 50's and 60's seem so eager to kill and mame people?  You could consider gutting the thing and sticking one of these bad boys in http://www.samedaymusic.com/product--MACM4000  (You'll also need to upgrade the speakers)