EARLY 90's FENDER BLUES DEVILLE SOUNDS REAL MUDDY, CAN'T READ BIAS CURRENT

[FriedWires]

Hi, I have searched all the threads on blues devilles & haven't found what I'm looking for. My problem is a friends fender blues deville I'm working on. I have worked on several old tube amps & this one has got me baffled. First it sounds muddy, tubes have been changed & even performed a torres mod to make it brighter- still muddy. OT? Haven't tested it yet. Are these amps just like that? Second when I went to measure the bias current between pin 3 on the 6L6 & the OT centertap, I get no reading! What am I doing wrong? I know there is a test point, but I was looking for the current. If anybody could help me out I'd greatly appreciate it. Thanks

[Enzo]

Pin 3 of the power tube is the plate, and to measure current between there and the OT CT your meter must be set up for current. On my FLuke for example, that means plugging the red probe into a different jack on the meter, as well as setting the meter selector switch to DC current.

Did you try on both power tubes? If the tube you chose was not running, as when a screen resistor is open, then there wil be no current to measure.

Pin 3 on each socket can be inconvenient to access, the push-on termnials for the blue and brown wires t the OT are the same thing and may be more accessible.

Isolate the problem. Run a cord from the preamp out jack to some other amp. How does the preamp signal sound coming out over there? And also, plug the guitar into the power amp in jack. You are bypassing hte preamp, but does the resulting sound come out clear and strong, or does it sound like your problem?

The Blues Deville has no test point. The Blues Deville Reissue has a test point. The Blues Deville has no bias adjustment, so no need for a test point.

Power off, resolder all 8 pins of both power tube sockets.

Powr on, check voltage on pins 1 and 6 of the phase inverter tube. Either one missing? Got roughly 35v at pins 3,8?

Check BOTH power tubes, is there B+ on both pins 3 and 4? Is there a reasonable bias voltage on both pins 5, about -50?

[Krwkka]

... and there is always the possibility that the speaker is kerfunken.

[Enzo]

Very true, or plugged into the EXT SPKR jack instead of the main speaker jack.

[FriedWires]

Hey, thanks guys for the info. I have replaced the speakers & tried another speaker cab(proper ohms load) with the same result. It is in the proper speaker jack. I have a fluke 87, had it set up properly to read DC current in ma. I will retrace my steps & double check everything that you recommended Enzo. I will post my results, hopefully just missed something. Thanks

[FriedWires]

Hey, it was a simple screen resistor like Enzo had mentioned. I replaced both & resoldered the output tube sockets to the board. I have learned my lesson well by not assuming anything is working. The problem was right in front of me! Learn something new every day. Thanks, again

[jhelm_waterw]

Glad you found your problem.
But what I was going to suggest is similar to what you said about not trusting anything INCLUDING the multimeter.
I've pulled out a multimeter to measure current and gotten nothing... scratched my head and retried 20 times only to find I blew the .5 amp fuse inside the multimeter
in a previous test.
I hate those days...

[Enzo]

And we all know WHY we have that fuse blown, it is because we slipped and grounded one meter probe. I have done it more times than I care to admit. Better that little fuse than a dead meter.