Amp troubleshooting question... Silverface Champ.

Well, you know it's not the bias supply cap... cause it doesn't have one. :-) That's the first thing I look at on Silverface Fenders.
 
It could be this guy:
 

 
Especially if the thing has been stored more than used.
 
The small coupling caps can last and last.
 
I'd take a look at the small electrolytic cathode caps on each tube... tap them with an insulated stick and see if you can excite the problem.
 
I have found that simply playing the old Champs keeps them going ok... and when I store them I have to play them back in to shape.
 
If you can leave it on while being near enough to unplug it... then I'd just leave it on for hours and hours and see if the caps freshen up a bit.
 
I actually went through the process of burning one back into shape just last week.
 
Just for grins, I'd pull the speaker connector (WITH THE POWER OFF) and plug it back in just to clean the contact.
 
Should be a fun troubleshooting project.
 

 
 
 

Hi Julien,
 For what it is worth... the orange drop (a.k.a. Polypropylene) caps are the very least likely to fail.
 
 The little 25uF/25vDc electrolytic caps can get old and dry. They are cheap and the Champ is easy to work on.
 
 I like to figure out what's wrong before I start replacing stuff... but sometimes that's the only way to find out what was wrong.
 
 The big filter cap I posted a photo of is sort of a pain. C.E. Manufacturing is making them on the old Mallory gear but many folks say the old ones were better. You can get one at Antique Electronics if you think that is something you want to mess with. If you do, please REMEMBER that this is the filter cap and it's the one that can knock you through the wall if you don't discharge it before working with it. You should always discharge that cap before poking around inside... but it's especially important if you are going to work in that part of the circuit.
 
all the best,
mike

mike_mccue
Hi Julien,
 For what it is worth... the orange drop (a.k.a. Polypropylene) caps are the very least likely to fail.
 
 The little 25uF/25vDc electrolytic caps can get old and dry. They are cheap and the Champ is easy to work on.
 
 I like to figure out what's wrong before I start replacing stuff... but sometimes that's the only way to find out what was wrong.
 
 The big filter cap I posted a photo of is sort of a pain. C.E. Manufacturing is making them on the old Mallory gear but many folks say the old ones were better. You can get one at Antique Electronics if you think that is something you want to mess with. If you do, please REMEMBER that this is the filter cap and it's the one that can knock you through the wall if you don't discharge it before working with it. You should always discharge that cap before poking around inside... but it's especially important if you are going to work in that part of the circuit.
 
all the best,
mike

Thanks, I've built several 5F1 amps and have been shocked once. I try to always keep one hand in my lap... thanks for the warning though, one cannot hear it enough. I've dealt with AE and CE and have accounts at several other parts companies. I thought it might be a cap but thought I'd ask in case someone had dealt with this particular symptom. I really struggle with schematics, I can figure them out if I really study and if it isn't to complex... but a good wiring diagram like for the early Fender amps REALLY helps me out. FWIW, I really prefer ceramic speakers in my Champs, especially the 5F1s, the alnico speakers get muddy too quick for me. I learned a trick for ALL Fender amps from a friend on a guitar forum... a Boss Bass EQ pedal. It will remove the woof and boominess from any Fender. The regular EQ is good too but the Bass EQ is something I always use with my CVR or other Fender amps,it really makes a big and good difference and it is a cheap addition. Try one with your Fenders if you get a chance, just roll the bass down a tad on the first two sliders... it is an amazing difference.. then if you want you can bump 800 up just a little and put a Marshall spin on it. I have 2x10 Ragin Cajun speakers in my Lux and LOVE it.
Sorry to ramble and thanks for the help! I will be in Thomasville on the 17th, some time when I am going to be in Moultrie for more than a couple of days perhaps, if you have time I can drive down to Tallahassee and buy you lunch... if you want. I sometimes have to drive my parents down there to see Dr. Forsthoefel.
 
Julien

 
I'd enjoy meeting up one day too. I have a gig on the 17th and 18th but I do look forward to meeting up someday.
 
Please keep in mind that I sort of jumped out the gate speaking about the capacitors (mainly because you said it had been stored). If I was playing it and heard it go weak as you describe I'd also consider the output transformer and of course the speaker as possible issues, but frankly I have run Champs well beyond where they should go and I've never hurt either the speaker or the transformer so mentioning it is just CYA. :-)
 
all the best,
mike

ampfixer
The can cap is the likely suspect, as Mike has pointed out. The other thing to check is the cathode bias resistor and bypass cap. There is a 250 ohm resistor on the output tube cathode along with a 25/25 electrolytic cap. I like to change the cap for sure, and the resistor if it's way off spec.

Cool, I will check them. Thanks..
J