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Author Topic: Help with Vintage '68 Champ Amp  (Read 4395 times)

DeeJay

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Help with Vintage '68 Champ Amp
« on: January 28, 2014, 11:46:21 AM »
Hello All,

In the late sixties when I was around 10, I found a Fender Champ Amp under the Christmas tree. Next to it was a blue Harmony dual pick-up solid body electric guitar. The Harmony was given away a long time ago by my mom, but the Champ sat idle in the attic collecting dust for many years.

The amp is now once again with me and, except for a bit of oxidation on the chassis and few dried out wires, it powers up and sounds as good as it did through my teen age years.

I have one small issue for which I am hoping you can provide me some guidance. When I plug in my new Epiphone Sheraton II, I feel a slight tingle in the strings, and there is a noticeable hum from the amp. The hum disappears when I touch the strings. I recently swapped out the two-pronged power cord with a 3-pronged grounded plug, and removed the 'death cap' as recommended on a few bulletin boards.

I am living in Qatar and am using a 220 to 110v step down transformer to power the amp. I've tested my Epi with a 220v solid state Marshall amp and all plays well. I'm wondering if the old wiring is leaking voltage to the chassis? I'm also wondering about the grounding in this villa. The construction quality is less than desirable and it wouldn't surprise to discover there isn't a true ground.

Can you provide any suggestions to solve my problem, or should I simply shelve the amp until I return to the  U.S.?

Any feedback is greatly appreciated.

Orson Maxwell

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Re: Help with Vintage '68 Champ Amp
« Reply #1 on: January 28, 2014, 01:13:17 PM »
Hi!

This potential can indeed be leaking via the transformer's parasitic capacitance, and unfortunately I don't remember what trannys they used back then.

Where did you connect the third (ground) wire of the new cable in the amp? Is the 220/110 step down transformer grounded?
If you want something done well - do it yourself.

Roly

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Re: Help with Vintage '68 Champ Amp
« Reply #2 on: January 28, 2014, 09:34:08 PM »
Hi DeeJay, and welcome.


Quote from: DeeJay
In the late sixties ... it powers up and sounds as good ...

You are lucky.  Amps left for such extended periods often give trouble, in particular the power supply caps "dry out" and require gentle re-forming (or replacement) before they are put back into service, so you have got lucky with this one.

Quote from: DeeJay
I'm wondering if the old wiring is leaking voltage to the chassis?

No.  That's not how it works.

Quote from: DeeJay
I recently swapped out the two-pronged power cord with a 3-pronged grounded plug, and removed the 'death cap' as recommended on a few bulletin boards.

That's good, but to be specific, you did connect the new three-core ground wire securely to the chassis, didn't you?


This effect could be due to dubious earthing of the building, but some stepdown/isolation transformers aren't brilliant at carrying the earth through to the appliance either.
If you say theory and practice don't agree you haven't applied enough theory.

DeeJay

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Re: Help with Vintage '68 Champ Amp
« Reply #3 on: January 29, 2014, 11:07:13 AM »
Thanks for the feedback (no pun intended) to all.

I may have solved the issue. The transformer I am using is a 2-prong, french style (round pegs) plug that I was told is not grounded.

I'm wondering: If I attach a wire (speaker wire for example) to a screw on the transformer box and connect it to the wall socket, will this provide a ground?

Yuppers, I grounded to the chassis. I had an electronics teach as my office do the soldering based on a wiring diagram. (I know just enough about circuits to be dangerous, but haven't smoked a device yet! :dbtu: )

Cheers,


phatt

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Re: Help with Vintage '68 Champ Amp
« Reply #4 on: January 29, 2014, 11:32:14 PM »
Hi DeeJay,
I'd suggest you get advice from a qualified electrician in your part of the world as messing with this by print can easy lead to confusion causing DEATH. 8)

You likely need the *correct plug* and some help from experts who know exactly how to wire up in a safe manner.
Phil.

Orson Maxwell

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Re: Help with Vintage '68 Champ Amp
« Reply #5 on: January 30, 2014, 03:55:37 AM »
We have a set of standard regulations regarding electrical wiring in living areas here in Russia that are obligatory for following. If you mess with these and someone gets hurt because of this - you go to jail, so it is serious stuff
Naturally they changed over time, and any old equipment is always a pain in the side, therefore I totally agree with phatt - its better to consult with a certified electrician.
If you want something done well - do it yourself.

Roly

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Re: Help with Vintage '68 Champ Amp
« Reply #6 on: January 30, 2014, 07:41:06 AM »
Quote from: DeeJay
The transformer I am using is a 2-prong, french style (round pegs) plug that I was told is not grounded.

That's right, 2-prong can't be, must be 3-prong in to be grounded, and 3-prong out to carry the ground through to the appliance (amp).

But I agree, safety grounding is tricky enough and important enough that you need skilled assistance on the spot.
If you say theory and practice don't agree you haven't applied enough theory.

J M Fahey

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Re: Help with Vintage '68 Champ Amp
« Reply #7 on: January 30, 2014, 04:57:19 PM »
Please search for the correct French page describing how is grounding accomplished there, electrical safety rules, etc. , and post links here.
Pas de probl├¬me pour lire Fran├žais ici ;)

Roly

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Re: Help with Vintage '68 Champ Amp
« Reply #8 on: January 31, 2014, 10:11:16 AM »
http://en.wikipedia.org/wiki/Mains_electricity_by_country
Qatar
240V 50Hz




Basically British standard.

I'll bet the stepdown tranny doesn't carry the input earth through to a the output socket - new three-pin (US) socket required with proper safety earth available.
If you say theory and practice don't agree you haven't applied enough theory.