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blown transformers


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5/22/2000 12:04 AM
bryen blown transformers
hi, i have a 4 6l6 amp and thought the OT was blown. i took it in to a tech i don't really know and he wants to replace both the output AND the power transformer. i didn't think they could both be broken. is it normal or possible for both to go out the same time, or is he maybe trying to do extra work. just wanted to make sure.  
thanks  
bryen
 
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5/22/2000 12:07 AM
Jim S.

What's the exact make and model of your amp, and what were the symptoms?
 
5/22/2000 12:24 AM
Carl Z

Bryen;  
 
I suppose it's possible but I've never seen both let go at the same time. The only thing is maybe somebody was running the wrong tubes and/or had the tubes wayyy underbiased and wants to replace them both just to be on the safe side. Had a Fender in here a while ago with a PT that was rusted beyond belief. Probably should have put a new one in but it still worked and he's not having problems.  
 
I'd say get some clarification on why he wants to replace both of them. Read RG's tube amp FAQ in the tube section to cross reference what the tech is saying. Be sure cause transformers aren't cheap!  
 
Regards;  
Carl Z
 
5/22/2000 1:43 AM
Bruce

Although not impossible, I've never had an amp in for repairs with both blown at the same time either.  
Have you been running the amp with 20 amp fuses because the standard fuses keep blowing?  
Tell him to prove it or take it somewhere else.  
 
Speaking of 20 amp fuses, I had a little tiny Silvertone 6V6GT 5 watt amp in for a minor tune up this week and the owner was running it with a 20 amp fuse.  
Ha ha .. I don't why I think that's funny.  
Bruce
 
5/22/2000 10:46 AM
A.S

20 amp fuses???  
I guess itīs OK to laugh as long as itīs not your amplifier.  
Look at it this way:  
Bloopers like that is what keeps techs like yourself busy.  
 
A.S
 
5/26/2000 1:53 AM
Rick Erickson

quote:
"20 amp fuses???"
 
 
I call those "universal replacement" fuses :)  
fwiw - I'm having a run on power transformers this month. So far I've had a Princeton, Champ, Marshall JTM30 and a Vox AC15 with fried p/t's. Strange!  
 
RE
 
5/22/2000 4:37 PM
Jim S.

I would say that whenever I get an older amp in for servicing, it has the wrong type or value fuse AT LEAST 50% OF THE TIME (might even be closer to 70% -- I should keep track and compile statistics!).  
 
Usually, it's not way off -- maybe there's a 3A slo-blo fuse instead of 2A slo-blo, or there's a 3A slo-blo in there and the schematic calls for a 3A fast-blo. But every once in a while I see something like a 20A automotive fuse in there and I'm glad for the customer that he or she got the amp to me for servicing BEFORE a power tube shorted out. A 20A fuse is no better protection than a wad of aluminum foil (which I've also seen on one occasion -- but in that case it was too late; a shorted screen had taken out the choke before the grid resistor could fully open up).  
 
The moral of the story:  
 
IF YOU'RE A TECH, ALWAYS MAKE SURE THE FUSE(S) ARE CORRECT, FOR EVERY AMP, EVERY TIME !!
 

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