Blues Deluxe Reissue-No Sound

[Perkinsman]

Hi guys, the amp powers up, all the tubes test Good, the tubes light & I resoldered the tube pins. I plugged into the FX return and still very low sound. Does this mean that the problem is in the preamp?

[DrGonz78]

Hi guys, the amp powers up, all the tubes test Good, the tubes light & I resoldered the tube pins. I plugged into the FX return and still very low sound. Does this mean that the problem is in the preamp?

If you plugged into the FX return that bypasses everything before it, which includes the preamp. So the problem points to the power amp side of the amp. To make sure the preamp is working plug into the main input and connect the FX Send to another amp. That will test the preamp to hear if it is putting out a strong signal.

Edit: Please post the schematic you are using to diagnose this amp too.

[xtian]

If you plug a guitar into the FX return, the volume will be low, but should be clear. You can also plug a line-level signal (like a CD player or smart phone) into the FX return, and you should be able to get a nice loud (still clean) volume out of the power section.

Also, try jumpering the FX OUT to FX IN jacks with a 1/4" patch cable. This will eliminate any malfunction of the FX switching jack's performance from the equation.

After these tests, if sound still fails to get from the preamp to the power amp, I would suspect a failed preamp tube, and work from there.

[DrGonz78]

If you plug a guitar into the FX return, the volume will be low, but should be clear. You can also plug a line-level signal (like a CD player or smart phone) into the FX return, and you should be able to get a nice loud (still clean) volume out of the power section.

Also, try jumpering the FX OUT to FX IN jacks with a 1/4" patch cable. This will eliminate any malfunction of the FX switching jack's performance from the equation.

After these tests, if sound still fails to get from the preamp to the power amp, I would suspect a failed preamp tube, and work from there.

I re-read the title of the thread "No Sound". So yes Xtian is probably right that it is an high impedance audio source plugged into FX return, so yes try line level signal. Patch cable will rule out bad switching jacks.

[Pedro Vecino]

Is the speaker jack connected where it should be?

[Perkinsman]

I did check to make sure the speaker was in the correct jack. I ran the above tests & still no sound. The preamp tubes are new & tested “Good”, the 6L6’s are not new but tested strong. I do have a question regarding:
“Also, try jumpering the FX OUT to FX IN jacks with a 1/4" patch cable. This will eliminate any malfunction of the FX switching jack's performance from the equation.”.
Does this mean jump fx send to fx return on the same amp? Or do I also plug the guitar into the input as well?

[The Dude]

Yes, jump fx send to return and plug the guitar into the input jack as you normally would. This takes the switching jack out of the equation.

If that doesn't work, I'd also check plate voltages on preamp tubes. I've seen open preamp plate resistors often enough on these amps. Or, just do a quick resistance check of each plate resistor.

[Enzo]

In my experience, my guitar plugged into the FX return makes a nice strong signal. Maybe not full power, but certainly not hard to hear. A CD player works fine too, that was my standard bench signal.

[Perkinsman]

Yes, jump fx send to return and plug the guitar into the input jack as you normally would. This takes the switching jack out of the equation.

Still no sound.

If that doesn't work, I'd also check plate voltages on preamp tubes. I've seen open preamp plate resistors often enough on these amps. Or, just do a quick resistance check of each plate resistor.

All Preamp plate voltages (except V2b) are running approx 240 vdc. All 5 plate resistors were good, not sure which resistor is on the plate of V2b. I can't find a schematic that shows expected voltages but these seem reasonable.

I tested the speaker with a 9v. It clicks but I don't see it moving back & forth. Should it?

[The Dude]

Yes, the speaker cone should move out if battery + is to speaker + (generally). You may have a shifted speaker gap- magnet/pole piece problem. I'd try the amp with a known good speaker. If you push lightly on the speaker cone, it should move in and out. If not and it's frozen, it's done.

[Perkinsman]

I tried another speaker & still no sound, this one is fine. What kind of voltages should I expect from the preamp tube plates? I’m getting around 240vdc but V2b shows zero. 420vdc on the power tube plates. Bias at 59mv.

[glebert]

I tried another speaker & still no sound, this one is fine. What kind of voltages should I expect from the preamp tube plates? I’m getting around 240vdc but V2b shows zero. 420vdc on the power tube plates. Bias at 59mv.

V2b is not used and is grounded out according to schematic. https://www.thetubestore.com/lib/the...atic-Rev-A.pdf
240V sounds right for the plate voltage on the preamp tubes to me. You have 345V node voltage at "x" and if a triode draws 1mA with 100k plate resistors is should drop 100V from the node.
Do you get any sort of pop at the speakers if you probe V3 with the power tubes in? Specifically pins 1,2,6,7.

[Perkinsman]

Yes, I get a pop on each of those on V3.

[Perkinsman]

I do have VERY low volume from channels 1& 2.

[Perkinsman]

I just used my signal generator hooked up to a 1/4” jack to inject a signal at the input (channel 1) & got a strong, clear, loud signal...but when I plug the guitar in, very low volume.