Trying to fix my friend's Fender hot rod deville.

[Loudness250]

I've had my friend's amp for awhile, quite a while. The problem was that it would not turn up loud. It sounds fine but just quiet. Things I have done to the amp are
1.replace preamp tubes with known good ones
2.Replace the main filter caps.
3.Change any resistor that I found dead, which there were a few.
4.Change the large ceramic block resistors.
5.looked for cracked solder joints which I really didnt find any.

Now the amp is slightly louder but not much. If anybody has any ideas let me know, thanks. BTW my friend has another amp but I would still like to fix this thing for him.

 

[Loudness250]

Bump

 

[jamme61]

I had the same problem it was the plate resistor- they're only 1/4 which is to small IMHO. you could trace the signal and see where it dies - (signal tracer) good luck

Try first
OH also try to jump the effects loop with a small patch cable

check this link BYO tracer http://billmaudio.com/wp/?page_id=1254

 

[Travis]

Make sure you are plugged into the right speaker jack. It sounds like really weak signal (or no signal at all) in the Ext. Speaker jack. It should be plugged into the jack next to the fuse. I did that once and was chasing my tail for 30 mins until I swapped the speaker cable and presto: loud amp. After checking that:

Do you have adequate signal if you plug directly into the "Power Amp In"?
If so, the power amp is healthy. There is a problem in the preamp somewhere. A scope comes in handy for this, but you can also tell if signal is getting through certain stages by measuring AC on the "pot" side of any coupling cap (not the high voltage side). You should have pretty big swings in AC with the signal as you play; if you use a signal generator, that voltage will be pretty much constant.
If it doesn't pass signal (or it's weak
Check the screen grid resistors and the plate resistors for the PI (I think they are the typical 82k/100k arrangement). I also remember a problem with the PI and the ribbon cable that connects the tubes to the main board: those solder joints are always pretty sketchy. There is probably a bad solder joint somewhere on the board. Chopsticks come in handy here to find the general area by pressing on the board itself as well as pressing singular components.

Those amps are a nightmare to service if something goes wrong: the boards are pretty awful and they tend to get really hot from the big dropping resistors for the channel switching supply.

I actually heard a Fender rep say once "We only make our amps to last about 5 years out in the field."

That way they sell more amps...