Fender DeVille 212, low low power

[featuringbirds]

I also tried swapping out the power tubes for another pair, same symptoms

[acorkos]

check the preamp and phase inverter plate resistors....

R4 100K
R11 100K
R16 100K
R22 100K
R57 82K
R58 100K

meter them to see if they're in spec, and check for high DC voltage on the tube side of the resistors

[Enzo]

The speaker is plugged into the right jack, OK, but did we test the speaker? Plug the speaker into some other amp. Does it work OK?

Have we decided which half of the amp has the problem?

PLug the guitar into the FX return. Does that sound clear out the speaker, or low and crummy?

Plug the guitar into the input out front, and connect the FX send to the input of some other amp. Does the FX send sound OK coming out the other amp, or does it have the problem. No point in checking voltages all over the preamp if the problem is in the power amp, and vice versa.

[Lee_ranaldo]

those fenders have an IC after the pre-amp stage
yes. an IC. that comes from the reverb recovery stage

They usually short and burn after a tube failure or some mystical intervention
Check it and replace it.

I saw the same problem on a blues deville i had here.
Customer brought the amp
minutes later (of use and testing)
bam, low power, crackled sound..

Check for U2 an TL072 Dual OP-Amp.

[featuringbirds]

Ok. Speakers tested fine.

Plugged the FX send into the input of another amp. Sounds plenty clear, volume control works. Is is safe to say that the pre-amp is OK?

Plugged the guitar direct into the FX return and it sounds quiet and distorted. Master volume still doesn't seem to have any effect on the volume or sound at all, just a small amount of signal passing through.

[Lee_ranaldo]

if i remember correctly the FX send signal comes before the suspicious IC i mentioned earlier.
that's why u get a clean signal if u send the pre-amp output to another amp
but when u plug a signalp into the power amp in , it sounds distorted
because the first thing that signal sees is the U2 TL072 OPAMP that is burnt

Just replace that TL072 opamp! :P

[Enzo]

Costs little to find out. But I woulod point out that when teh FX loop is NOT in use, the signal path does not run through either side of that IC.

[featuringbirds]

How can I find out if the signal is getting past that point? Or can I test the op-amp Lee_ranaldo mentioned before I go throwing parts at the amp?

[52 Bill]

If you read what Enzo posted, the IC is not in circuit when the FX loop is not used. So it doesn't matter if the IC is ok or not until you get the original problem solved, which appears to be in your power amp.

Did you ever try changing the driver tube?
Do you have a voltmeter? Have you checked the voltages in the power amp and driver stages?

Try cleaning the extension speaker jack switch contacts.

[Jerry]

Check R57,58. These are the plate load resistors for the phase inverter and I have seen these resistors open up on a few of these amps.

[featuringbirds]

How can I check resistors in circuit? Or will I need to remove them? not a huge deal either way.

[MWJB]

If you are checking the plate resistors at V3 (pins 1 & 6) you just need to measure the voltage at the tube pins, should be within 15v of each other (see Devilles schem at Fender.com). If one of the pins has no voltage then the resistor that feeds that pin is open & needs replacing.