[sdiy] Old Fender amps

[metasonix]

At 09:46 PM 8/2/03 -0700, you wrote:
>Speaking of old Fender amps - I have an old Bandmaster head, I think 
>it's about a '67. It definitely is the AB763 circuit. I hadn't used it 
>in years, and I tried powering it up and it blows fuses. So after a bit 
>of research, I figure I need to replace all the electrolytic caps. I 
>opened it up, and sure enough, one of the filter caps has goop coming 
>out of it. So I buy caps, replace them all - and it still blows fuses. 

You forgot to check the bias circuit. It has a small electrolytic (or two) and
a diode, and either one is often bad. No bias means the output
tube grids are not biased negative, thus the tubes are drawing full current.

Also suggest you get new 6L6GC output tubes. Not Chinese, please.
Sovtek, Svetlana or JJ are good quality. You can get them from any
number of online tube dealers. The stuff you get at music stores is
often Chinese, regardless of the brand. Fender, Mesa and Groove Tubes
all sell private-labeled tubes that are really Chinese made. 

Older Fenders often blow up when they get Chinese 6L6s, because of 
high plate and screen voltages. Current 6L6 guitar amps only run about 
400v on their tubes for this reason. The problem is mainly the screen
grid getting too much voltage/current.

>send it to uncle eric. I 'hear' he fixes old Fender amps for $40 or less...
>don't let him try to 'rip you off' by charging you more...
>hah hah hah hah   :^P

I just saved you a $300 service job, Scott....

Did I ever tell you about the Acoustic amp I once saw, a 1978 model that
ran 750 volts on four 6L6GCs? People who own those things are having
real problems nowadays...poor bastards...



uncle eric
metasonix.com