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#1 2012-07-15 20:16:47

RickyLee
New member
From: Riverside CA U.S.A.
Registered: 2011-06-06
Posts: 3

Ampeg V4 Front Panel Removed While Powered ON

Had a strange thing happen with this '73 Ampeg V4 I am troubleshooting looking for an intermittent bug. I am hoping I can find someone with some experience working on Ampeg amps here. Basically I am trying to find out if this front panel piece is known to cause some strange incidents with B+ shorting to Ground/Common.

The front controls PCB is mounted to a metal piece section that is screwed down to the rest of the main chassis. I removed all the screws and slightly pulled back this front panel to be able to see this controls PCB a bit better. I then powered ON the amp. When I went to plug my guitar into the front input, I was holding on to the chassis and got a slight tingle and shock from the chassis. As I let go of this front panel piece and main chassis, the front panel moved around slightly. Then there was some loud crackling, power valves flashed and the amp shut down. End result was it tripped my GFCI wall receptacle when this happened.

The standby switch circuit is the B+ voltage completed/return path to Ground/Common. So when I moved that front panel around, it acted like the B+ was shorted to Ground - a loud crackle, power valves flashed and tripped my MAINS GFCI on the wall. The only thing associated with the B+ on that front panel piece is the standby switch. But when the panel was secured with screws, I wiggled wires and could not repeat the incident. There is one wire coming off that controls PCB that acted a bit suspect when I wiggled it. But I could not see anything with B+ associated with that front controls PCB. I will look into that wire when I work on it again.

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#2 2012-07-15 20:29:47

RickyLee
New member
From: Riverside CA U.S.A.
Registered: 2011-06-06
Posts: 3

Re: Ampeg V4 Front Panel Removed While Powered ON

I should add that I narrowed down the location of this intermittent problem to the tone circuit. I am going to change out those concealed components/"integrated circuit" with new components when I can order/get them.

Also should add that the POWER ON lamp flickers quite a bit and will flicker/dim slightly with the load pull on the amp while playing it. Was wondering if this lamp or the resistor should be replaced? And is the resistor inide the black wire/shrinkwrap?

Also, I should add that this is my second Ampeg V4, not the one I aquired last year. This one I am having the problem with is from early '73 and I already added a Grounded power cord to it.

Last edited by RickyLee (2012-07-15 20:31:00)

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