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Post subject: Problems with a SF VibroChamp - HELP!
Posted: Tue Apr 20, 2010 9:35 am
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My first post 8) I posted this elsewhere but I've read loads of interesting comments here so I might as well have a go, hope you can help me out :)

I'm having trouble with a '78 SF VibroChamp that started sounding ugly a few weeks ago.

The amp has lost about 60% of its volume and it sounds pretty distorted, like a broken radio. It produces a low distorted and fuzzy sound, even when I push it up to 10.

I tried new valves, still sounded awful. Tried swapping different preamp valves, nope. New rectifier, nope. New 6v6.... nah...

I've checked all voltage readings on the layout and there's nothing wrong there, some drift a bit but there's nothing out of the ordinary. Resistors are ok, caps I haven't checked yet but the voltage readings are ok on all caps.

Next step is to start reading the values of every darn component, desoldering the annoying ones, etc. funny thing is the voltage readings are ok? Never come accross something like this...

(It's a 78 model - I changed the bias resistor and cap to 1k 1W and 50uf50v and added a 470 Ohm 3W grid resistor but that was AFTER it started sounding like crap)

Help pleeeeeeeeaaaaaseeeeeeee


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Posted: Tue Apr 20, 2010 2:14 pm
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Joined: Fri Feb 05, 2010 4:31 am
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Have you try another speaker ?
Are you sure your guitar and wire are good ?

Have you a good voltmeter ? Brand :______


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Posted: Tue Apr 20, 2010 5:59 pm
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I repaired a '72 Bronco (or '74) with the same problem. Check the ground wires that come off the board to ground. The one I repaired looked fine, but didn't have a good connection. Reflow the solder on these and all the eyelets on the board. The ground for the 6V6 was the culprit in my case.


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Posted: Wed Apr 21, 2010 4:13 am
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rjake, you are right about solder around the 6V6. Or all circuits that feed the 6V6

I didn't know that amp have circuit board (printed circuit). That's made big difference in repair ( re point to point wiring).

Distorsion and low power look like a bad solder or contact aroud the 6V6. Or burn copper connexions between two parts.

Or at power resistors on the power supply that feed 6V6 and output transformer.

Bestron, Check all resistors and copper wiring go to your 6V6, reheat solder
Do you have the schematics ? If yes, can you send it or send the web adress where I can find it"

I look at many that I know and can't find it


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Posted: Mon Apr 26, 2010 2:26 am
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thank you very much guys, it was a faulty cap in the end!

this baby needed a recap so I simply replaced everything in there and now it's sweeter than ever :D

thank's for your time



:)


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