Dead Blues Deville

[WholeToneMusic]

On TP 30-34 everything looked in spec except for TP 32. Clean channel measures +15vdc and the drive channel measures the same. The schematic show the drive channel should measure -15vdc. I will continue to check more voltages and get back to you, thanks Bill.

[WholeToneMusic]

Update on Blues Deville

I ordered a couple of OP-amps and had to wait for them to ship. I put them in and the amp is still weak sounding. At TP4 and 6 I am getting 0 volts AC. TP 5 is 2.00VDC, which is in the park. I am thinking that C4 or C2 is not passing AC like it should. Any one have any suggestions?


Best Regards,
Brian

[52 Bill]

At TP4 and 6 I am getting 0 volts AC.

What is your input signal?

I am thinking that C4 or C2 is not passing AC like it should.

C4 is bypassed when the drive channel relay is on. Does the problem show up in both modes? You can try paralleling another cap across C2 to see if it is the problem. Just make sure that it's voltage is rated high enough.

I don't remember, did you try changing V1? What is the DC voltage at TP3?

[WholeToneMusic]

The signal was a guitar signal oops, I re-tried it with a 1kHz signal and they are in the ball park. I found that CR 24 and 25 were shorted out. I measured infinity out of the circuit on the diode check mode with the test probes hooked up both ways, so I replaced the two diodes. Did not help the power deficiency. Back to the drawing board.

[Mars Amp Repair]

Say,
have you checked the + and - 16V supplies for the opamps? You can access them from pin 4 (neg) or pin 8 (Pos) of any of the TL072 (or 4558) 4 legged IC's in there. glen

[WholeToneMusic]

OP Amp test points

Yes,

On U1-U4 i am getting -16.00VDC on pins 4 and +16.00VDC on pins 8.

[52 Bill]

I have tested the speakers through a different amp and they work. However when I plug the load into the amp there is no hiss or noise whatsoever. I have the speaker wire plugged into the jack that is connected to the secondary of the OT. The other jack is in parallel with the speaker jack.

I carefully re-read the entire thread and noticed this statement.

On the Blues DeVille the main speaker jack is the one not directly connected to the transformer. The extension speaker jack has a switch contact that changes the connection to the transformer secondary from 8 ohms to 4 ohms. If you plug into the extension speaker jack, the main speaker jack will still short the signal to ground.

I've also seen the switching connection on the jack become dirty and need servicing. Try cleaning all of the speaker jack contacts and be sure to plug into the jack that does not connect to the transformer.

[Twist]

One of the most common problems with these amps is cracked solder joints on the tube sockets . They're small and hard to see sometimes. On some I've seen open plate resistors on the PI. Are you driving the power amp input with a large enough signal? A small signal may sound clean but increasing it may reveal an issue in the power amp. I may have missed it in the previous post but what do you read in millivolts across R66 (or whatever it's designation is, it's tied to the output tube cathodes)?

[WholeToneMusic]

I carefully re-read the entire thread and noticed this statement.

On the Blues DeVille the main speaker jack is the one not directly connected to the transformer. The extension speaker jack has a switch contact that changes the connection to the transformer secondary from 8 ohms to 4 ohms. If you plug into the extension speaker jack, the main speaker jack will still short the signal to ground.

I've also seen the switching connection on the jack become dirty and need servicing. Try cleaning all of the speaker jack contacts and be sure to plug into the jack that does not connect to the transformer.

Thank you Bill for your attention to detail and taking the time to re-read the thread. Originally I tried the other jack however this was before I changed one of the switching transistors out that Enzo had recommended to check. I tried the other jack and it works beautifully. Thanks again everyone for your insight and time.

[WholeToneMusic]

Output better, Still no reverb

The amp's output is back however, the reverb is not working, I checked the tank with a meter and it measures within spec. when I shake the tank it crashes. I checked the reverb wire going to the board for continuity and all is well, The problem must be on the circuit board. I put a new OP amp in for the reverb and am still not getting reverb. Any suggestions?

Best Regards,
Brian

[52 Bill]

I checked the tank with a meter and it measures within spec. when I shake the tank it crashes.

What are the resistance readings of the tank's input and output coils?

Try reversing the leads to the tank and shake the tank. Still crash? Is the reverb back?

Signal trace the signal from the amp to the tank input. Feed it into another amp and see if there is any signal going into the tank. If you've already replaced U2 then there could only be a problem with the board or related components. What are the dc voltages on U2 pins 1, 2, 3, 4 and 8?

[WholeToneMusic]

Deville

Hello Bill,

I marked the leads before I disconnected them. The leads are fine. The op-amp had +16V and -16V for the input and output and the other pins measured 0. I will signal trace it when I get back into town. I wanted to get some ideas on it before I got back into town.

[WholeToneMusic]

DC voltages on U2

Hello Bill,

Back at the shop, Tested the U2 DC voltages, The results are

pin 1 78mV - 0 mV (it fluctuates until it hits 0)
pin 2 o
pin 3 .9 mV
pin 4 -16.65 V
pin 8 +16.68 V

Just for giggles I switched the reverb cablesa around and it didnt crash, I used a continuity tester on both in and out rca cables and they test good. I have not signal traced it yet. The input transducer measured 26 ohms and the output measured 200 ohms, thats spot on for the 4bb3c1b which specs at 26/200 so the tank is fine.

Best Regards,
Brian

[Mars Amp Repair]

Hello Bill,
the voltages you're getting on the drive side of the op-amp are normal. If you're not getting a crash from the tank & the tank is good, the...

the voltages you really need to be looking at are the ones on U-2 pins 5,6,7 (reverb recovery). Voltages should be pretty much 0V on all of those pins. BTW, just touch the rca plug that goes to the OUT tank jack & you should hear a hummm. that would take the tank out of the picture as far as the return side is concerned.

If voltages are good, then you may have a problem with the reverb muting circuit Q2. The NOT-reverb line from the foot switch circuit could also be faulty. That is one weird circuit to understand, so check the other more obvious things first.

If the NOT-reverb line is HI (reverb on) to gate of Q-2 , then it could be the FET. Best way to tell is to unsolder the Drain pin of the FET (the one connected to the reverb out signal) & see if your problem is resolved.

There's just not that much left in there to cause this issue. glen

[52 Bill]

Glen: I think he said it stopped crashing after he reversed the reverb cables, so I don't think that it is a recovery side problem.

Brian: Even if you reverse the tank cables there should be some crashing sound, it will be quiter that normal, but it should still make a sound.

You've checked everything there is to check, tank transducers are ok, the cables test ok for continuity and you've already replaced the reverb IC. So, you need to see if the amp is sending a signal to the tank. Scope the signal at the tank input lead and see if there is a signal present. If you don't have a scope, hook the output cable to a small amp or read the ac voltage at the cable end and see if the amp is sending a signal.

The only other thing to check is the RCA jacks and plugs for oxidation, etc. Clean and tighten all of the connections. Use a little Deoxit on a cotton swap and wipe down all of the contact surfaces.