Crate Blue Voodoo BV-120 Repair question

[jgcable]

Well, my great sounding BV120 (it sounded so good most of my musician friends were shocked) broke for no apparent reason. The 2 left power tubes stopped working and the 2 fuses blew for their lights. There are no cracks anywhere. The only thing I found was one of the fuse holders needed to be resoldered. I resoldered the fuse holder and I replaced the fuses. I fired it up and the 2 tubes wouldn't light up and the 2 fuses popped again. These are 1/4 amp fast blow fuses so I assume they are probably just for the lights.

Anyway... while I was poking around in there I found a few things that I can't figure out (I am not a full technician).

#1. The amp is running E34L's. Everything that I have found shows the amp should be running 6L6's.


D25 (which is a 1N4007 diode) has one side of it clipped. I have no idea why.

Everything else looks untouched.

I have a local repair tech shop that I could bring the amp to but he is SO expensive. It would probably cost me more for him to repair it than the amp is worth. I have never walked out of his shop with a bill less than $200 no matter what he ends up doing. Most techs around here are that expensive. $50 just to look at the amp.

Any ideas?

[paranoid]

I am not a tech by any means, but if I did not want to spend much money on it I would follow the tracks from the fuses and test each part in that line until I found what was blowing the fuses. Shorted caps, transformers, and diodes are big fuse blowers. resistors normally should not cause a blown fuse, but are easy to test.

[jgcable]

I am not a tech by any means, but if I did not want to spend much money on it I would follow the tracks from the fuses and test each part in that line until I found what was blowing the fuses. Shorted caps, transformers, and diodes are big fuse blowers. resistors normally should not cause a blown fuse, but are easy to test.

I can't find anything that tests bad except for the 1N4007 diode that somebody had clipped one side of it. I have no idea why that was done. I also can't figure out why my amp has E34L's in it instead of 5881's. I did 2 gigs with it so it worked with the clipped diode and the E34L power tubes. Then.. suddenly... it crapped out as explained above.

[toejam]

I also can't figure out why my amp has E34L's in it instead of 5881's. I did 2 gigs with it so it worked with the clipped diode and the E34L power tubes.

I'm pretty sure the BV series were able to run both EL34s and the 6L6/5881/KT66, you'd just have to make sure it's biased correctly for whichever set of tubes you want.
I had a BV60 head one time that came with KT66s and it sounded incredible.

[DonP]

You did try new tubes?

The diode is a protection device to keep from blowing up the output tranny if a tube shorts out. The fast blow fuses are also to protect the tranny. The trannies are the most expensive parts in an amp.

[jgcable]

You did try new tubes?

The diode is a protection device to keep from blowing up the output tranny if a tube shorts out. The fast blow fuses are also to protect the tranny. The trannies are the most expensive parts in an amp.

I didn't try new tubes but I did swap them around and the same side didn't work.
Any idea why the 1N4007 diode had one side clipped? Could it be some kind of mod so the amp could run E34L's instead of the 5881's.
The BV60 can run either. No bias pot either. The BV120 doesn't appear to be able to run EL34's from what I found online unless it has some extensive mods. Mine absolutely doesn't have extensive mods. The only thing I found is that 1 diode with 1 side clipped.

[DonP]

If the diode was fried, that might explain why it was clipped. Test the diode to see if voltage flows one way or both ways. If it flows both ways it is fried.

If it's not designed to run EL34's I'd be worried, especially if you can't set the bias. The tubes might be running hotter than the amp can handle.

Although most amps sound best when they are on the brink of destruction

[toejam]

Weird. I thought both the BV120 and BV60 could run either/or EL34s and 6L6. Guess it was modified in some way if it's not supposed to run EL34s normally.

[zeegler]

This is going back a ways, but I seem to remember that the 60 watt combo could run with EL34s or 6L6s, but the 120 watt head was strictly 6L6s. Of course I could also be completely making that up.

[cliffs_trip]

I had a BV60 which had a bad EL34 in it and it blew that diode in half. It also blew the 1/4 amp fuse for that power tube. The BV120 has the same setup as the BV60 except the diodes are on the power tube circuit board. I replaced all the diodes and put a set of 6L6's in and followed the auto-bias procedure on the BV60 and it came back to life.

The BV120 doesn't have the auto bias feature.

It does have a bias pot to adjust the fixed voltage going to the power tubes, though 6L6's are the only tube I've ever used in them, and am unsure if the power transformer could handle the current requirements for EL34's. I would stay safe and stick with 6L6's.


This gives me some fun ideas for an old BV120 of mine.

[jgcable]

UPDATE>.... I replaced the 1N4007 diode and 1 of the cement wire wound resistors. I put fresh tubes in and biased it to 42mv. It holds a fairly stable bias but I have another problem that popped up. Even though the amp sounds great and everything works fine it has a VERY VERY NASTY ground buzz.
Here are the symptoms...
No instrument cable plugged in... DEAD QUIET
Instrument cable plugged into effects return with guitar plugged in... DEAD QUIET
Instrument cable plugged in to input jack with guitar plugged in... TERRIBLE 60hz ground hum. Almost sounds like when you unplug your guitar and let the cord flop on the ground. If I touch ANY part of the metal on my guitar the buzz goes COMPLETELY away.
I have tried different cords, different guitars, different outlets, I even tried a 2 prong adapter that lifts the ground. No change.
It seems like something simple but I can't figure it out. Its not the input jack. I tested everything on it.
Any suggestions?

[cliffs_trip]

Is the buzz constant on both channels? If so I would say it is a part of the circuit they both share. Since we know it doesn't affect the effects return it can be narrowed to between those two points.

Have you tried pulling the preamp tubes one by one to see if the buzzing goes away? That may help to narrow down what part of the circuit the buzz is coming from. Shouldn't be a need to pull the phase inverter since it exists after the loop in the circuit. Have you switched out preamp tubes to make sure there aren't any bad ones?

Do any of the potentiometers affect the buzz?

Do you have an audio signal probe? They aren't too hard to build, if not. They can be used to pinpoint where in a circuit noise is being introduced. I would only use this option if you are aware of the dangers and safety precautions needed to be taken when working on high voltage equipment while it is on and operating.

Sometimes when caps fail they will introduce noise into the signal.

[jgcable]

Is the buzz constant on both channels? If so I would say it is a part of the circuit they both share. Since we know it doesn't affect the effects return it can be narrowed to between those two points.

Have you tried pulling the preamp tubes one by one to see if the buzzing goes away? That may help to narrow down what part of the circuit the buzz is coming from. Shouldn't be a need to pull the phase inverter since it exists after the loop in the circuit. Have you switched out preamp tubes to make sure there aren't any bad ones?

Do any of the potentiometers affect the buzz?

Do you have an audio signal probe? They aren't too hard to build, if not. They can be used to pinpoint where in a circuit noise is being introduced. I would only use this option if you are aware of the dangers and safety precautions needed to be taken when working on high voltage equipment while it is on and operating.

Sometimes when caps fail they will introduce noise into the signal.

The buzz is in both channels. Obviously.. its louder in the gain channel but its definitely there. I tried swapping and pulling preamp tubes with no change and none of the potentiometers affect the buzz. It sounds EXACTLY like when you unplug your instrument cable from the guitar with the amp on.
When its plugged into any guitar all I have to do is touch the strings and the amp is perfectly quiet.

[Ripley7t]

Bad jack/connection in the send/return of effects loop? Looking at the amp info, the two channels are totally separate, maybe something in the loop circuit. I had a Peavey XXL long ago that had issues due to the loop and also the tight/loose switch as well.

[jgcable]

Bad jack/connection in the send/return of effects loop? Looking at the amp info, the two channels are totally separate, maybe something in the loop circuit. I had a Peavey XXL long ago that had issues due to the loop and also the tight/loose switch as well.

The effects loop works perfectly plus the amp has a button that bypasses it or pads it and they both work fine too.