Crate BV120H (older blue tolex) noise problem

[Danglin' Fury]

On V1, between pin 2 and ground reads a short with nothing plugged into the input.

[Helmholtz]

On V1, between pin 2 and ground reads a short with nothing plugged into the input.

Good.

Other answers (V1 out, heater voltages, Sidac disconnected, heater balancing resistors, noise dependence on tone controls, any DC on LDRs)?

[Danglin' Fury]

The DCFIL1/2 Volage is 6.91 VDC. The noise does not stop when I pull V1. The noise is not dependent on tone controls. It is constant in volume and the tone controls cut all the bass, mid, treble like they should, bit the noise does respond with the turning of controls, not in volume, only in bass, mid, and treble content in the signal noise. Across the LDR in the V1 circuit, measuring the legs across the body of the LDR, one reading was 2.5VDC and the other side was 4.1 VDC

[Helmholtz]

The DCFIL1/2 Volage is 6.91 VDC. The noise does not stop when I pull V1.

Ok, thanks.

But in this special case I am interested in the 2 DCFIL voltages wrt ground separately, as I think a damaged Sidac might show in heater voltage imbalance. Also a high energy pulse that caused Sidac breakover might have taken out one of the balancing resistors.

The noise is not dependent on tone controls. It is constant in volume and the tone controls cut all the bass, mid, treble like they should, bit the noise does respond with the turning of controls, not in volume, only in bass, mid, and treble content in the signal noise

.

Sounds contradictory. If the tone controls change the sound of the noise, they do affect the noise and there must be noise signal at them. That's relevant for troubleshooting.

Across the LDR in the V1 circuit, measuring the legs across the body of the LDR, one reading was 2.5VDC and the other side was 4.1 VDC

None of the LDR's (that's the resistor part of the Optos) should have any DCV between its ends (not wrt ground).

[Danglin' Fury]

The DCFIL 1 and 2 are ~3.32 VDC rtg. Both read this. I lifted a leg of the SIDAC. it got substantially worse. In volume and it basically overtakes the main signal. I'm gonna resolder the SIDAC and see what happens.

[Helmholtz]

The DCFIL 1 and 2 are ~3.32 VDC rtg. Both read this. I lifted a leg of the SIDAC. it got substantially worse. In volume and it basically overtakes the main signal. I'm gonna resolder the SIDAC and see what happens.

As said earlier, measure both 470R balancing resistors.

[Danglin' Fury]

Out of circuit, they both read 464 ohms.

[Helmholtz]

Out of circuit, they both read 464 ohms.

Good.

Strange that disconnecting the Sidac changed your noise level. Can't think of an explanation.

[Danglin' Fury]

I reconnected it. Now it is a wall of noise that keeps getting louder til it is unbearable.

[g1]

I think there is another issue and the SIDAC is just coincidental. Suggest you leave it disconnected til the problem is resolved, then reconnect it to see if it is ok.
As you are working in that area and it seems to be affecting the noise, may be solder joint related. Does flexing board with a chopstick have any effect on the noise?

[Danglin' Fury]

I'm not sure. Now when I turn the standby off, like I said, the noise gets louder and louder until it is unbearable. I will know more tonight.

[Danglin' Fury]

Good.

Strange that disconnecting the Sidac changed your noise level. Can't think of an explanation.

I also forgot to mention that I changed C1 and C9. C1 is the .68uF cap in parallel with R3, and C9 is the coupling cap after V1, going into the Optocoupler and then into V2. I did those the same time I removed the leg of the SIDAC. Thats when the noise became a WALL of noise. I then replaced the Sidac and put the old caps back in and the wall of noise is the same. Completely unbearable. What would the consequences be of removing the Optocouplers completely and putting jumper wires there?

[Helmholtz]

We got sidetracked with this Sidac thing.

As things have changed, I would start again with pulling preamp tubes one after the other.

[Danglin' Fury]

I will do this as soon as I get home. I also noticed something. Befire it all went to shit, the noise is on both channels but the clean channel volume knob, I could move it around and it seemed to affect the noise. But that doesnt make sense for the dirty channel. Ya know, I could have easily busted some solder pulling the board out and putting it back in. First thing when I get to my bench, I will start pulling preamp tubes.

[Danglin' Fury]

Hey all... sorry but I've been busy with my Mom..anyway.. as soon as I pulled V1, the noise went mostly away. It is a very quiet crackling when I pulled it. Also, when all the tubes are in it, the dirty channel sounds pretty damn good. I can only perceive typical white noise. The clean volume does not make the signal go away. According to my meter, the pot is operating properly out of circuit. In circuit I read a short between the center wiper and the ground side when it is at zero, but the signal is still pretty loud. When I turn the volume up the signal does get louder but at zero it never goes away. I have also tried a different 1 meg pot. Same thing. The 50k midrange pot was reading 66.5 ohms at zero, even out of the circuit so I replaced it. No joy.