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Fender Champ question


 
10/7/1998 11:50 PM
Mark
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Fender Champ question
I have two questions concerning my mid seventies Fender Champ. The first question concerns a drop in volume that occurs when the amp has been on a few minutes. It happens intermittently and sometimes never at all. The volume never drops completly out. This is very irritating . I have never changed caps on this amp . I have however changed the power, rectifier and preamp tubes. ( the preamp tube was slightly used though.) My second question probably wont be as straight forward. I have played on several other Champs and Vibro Champs from this time period. Most of them gave a nice overdrive when cranked. Mine soundx trebly and does not break up smooth at all . What gives?
 
10/8/1998 6:53 AM
J Fletcher
Sounds like it could be the speaker.I've seen these same symptoms before, and it was an intermittent in the the speaker coil. Could be lots of other things too, but I'd check that speaker,since you've already replaced the tubes. Connect a good speaker up and see if your problem clears up...
 
10/8/1998 9:03 AM
Whit
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Mark,  
 
After checking the speaker like Jerry suggested, the next culprit could be some of  
the electrolytic capacitors inside the amp.  
 
I'd be suspicious of the power supply caps and the cathode bypass caps, particularly the bypass cap on the 6V6GC power tube.  
 
The cathode bypass caps boost the gain, volume and bass response in this circuit, so if they were flaking out (due to heat?) you'd end up with a trebly not so overdriven sound.  
They'd be the little 3/4 inch cans with 25/25 marked on 'em. (25uf, 25 volts).  
 
Remember above all else that lethal voltages exist in this amp, so if you've never been in there before, seek qualified help.  
 
... Whit
 
10/8/1998 9:49 PM
Mark
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Thanks to both of you for your input and advice! I have been in there Whit and I will be extra careful. One thing I would like to know, Do I need to form those caps with a variac and is there any way to check the voice coil accurately? And also what would be a good (economical!) replacement speaker?
 
10/9/1998 12:48 AM
Bruce
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If it is an 8" 4 ohm speaker, the only guitar speakers I know of are Eminence and Ted Weber's custom speakers.  
Which, by the way, are way cool.  
Anyone else?  
The reformation of E caps is a controversial subject Mark!  
Low voltage caps probably don't need to be reformed unless they are absurdly old.  
If the caps are relativly new you probably don't need to reform them either.  
I'm sure Fender, Marshall, etc never did.  
If you are worried about it anyhow, use a highish value resistor in series with the cap supply voltage to limit the current for a little bit of time for a few cycles of on-off.  
Personaly, I've never blown up, or to my knowledge, damaged a supply cap by not reforming it..... even if it was 4, 5 or more years old for that matter, I have never blown up an E-cap at all in a guitar amp.  
I've seen PLENTY of them leaking all over the place in old amps and lots of vents popped in old Fender etc etc....  
While doing 2 way radio repair years ago, I accidently replaced a 1000uF/25v cap with a 1000uF/6 volt cap in split voltage supply ...and it blew up.  
Right on my bench while I was tuning the RF stages! Startled the bejezzes it of me.  
It sounded like small caliber pistol shot!  
It made a mess in there too.  
I made a mess in "there" too.  
 
Bruce
 
10/9/1998 7:00 AM
Steve M.
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Mark,  
 
FWIW, I had a Silverface champ a while back with one of the Eminence speakers Bruce mentioned. They are pretty inexpensive, I think I paid $35 for mine. It doesn't sound all that great, kinda harsh when the amp was overdriven, YMMV. The Weber speaker will probably sound great given their reputation but will probably be double in price of the Eminence. Kendrick also makes a champ replacement speaker but the cheapest I've seen it is about $55 from AES in Arizona. I've also heard that Celestion makes a champ replacement, but don't know for sure, I could be wrong.  
 
Steve
 
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