Crate Blue Voodoo BV-120 Repair question

[cliffs_trip]

Going back to what you said in a previous post, Since the amp buzzes unless you touch something metal, that is usually a sign of a ground connection not being made properly. Had an issue with an output transformer not having a secondary ground a few weeks back and the amp hummed loudly unless you touched the chassis or metal on the guitar.

The input jack is a shorting jack, which means it shorts its self to ground when you pull the guitar cable out. So if the buzz stops when you pull out the cable or touch metal, it gives the signal a path to bleed off to ground.

I would check all of the inputs and speaker jacks to make sure all the solder joints are not broken or compromised. A failing connection can cause some noise, but it is usually a crackle type noise, though bad grounds hum, and hum badly sometimes.

I had a JFET go out in a Crate Stealth I have and it caused the clean channel not to work as it shunted all the signal to ground through the broken JFET. Narrowing your issue down may not be easy without a signal probe or oscilloscope, as with the issue I had with the Stealth, when checked with a signal probe, the signal was fine all the way through the circuit until it left the master volume. The JFET was trashed and instead of switching the clean channel back into the circuit path, it shunted it to ground instead. It even made the Master volume control appear to work backwards for the clean channel.

I have an old BV120H circuit board to look at, but there are a ton of components between where your signal is clean and where it is humming. The easiest way to figure out what is wrong would be to pinpoint where exactly the buzz is coming from. If we know what part of the circuit then we can more accurately diagnose the cause.

Have you cleaned all of the jacks and potentiometers?

Given any though to building an audio signal probe?
Here's a link to a video of a person demonstrating how one is used to find a problem in an old tube radio.

https://youtu.be/maIJC4J_jZw

[jgcable]

UPDATE..... I found out what the ground problem was. It was a bad power cord. 1st time that has ever happened.
I have another question. I have the amp hooked up with my meter and I am checking the bias to see how stable it is. I notice 2 things....

Keep in mind... I am using a set of 5881 Mesa tubes and a set of 6L6 GT tubes in it. The GT's glow a little blue.

When I set the bias to 42mv... after about 10 minutes of warming up.... it drifts anywhere from 39mv to 46mv.
I also notice that the large yellow wire coming from one of the transformers gets pretty hot. Not melting hot.. not burning hot.. but definitely hot.
Besides those 2 things the amp seems to be running and sounding fine now.
One last question... If I wanted to run the amp with only 2 tubes which 2 would I pull? The 2 left or the 2 right or the 2 inside or the 2 outside?

[DonP]

Pull the 2 inside or 2 outside. You need to mis-match the amp ohm output with the speaker ohm output. Google search - I can remember if it's 8 -> 16 or 16 -> 8.

Bias drift is just bad design. Components are undersized for the current they need to handle and heat up. Heat increases resistance and throws the circuit off.

Blue glow is fine. Red (metal plate) glow is bad.

That hot yellow wire might make me worry. I'd try to find out what it is doing.

[cliffs_trip]

I believe the yellow wire is the filament voltage. Have you tested your filament voltages? The only reason I would expect it to be hot is if there is a higher current draw than what it is designed for. Could also mean an issue in part of the circuit attached to the filament voltage circuit. I seem to remember they ran the heaters DC in the first couple of stages of the amp then further up the chain switch to regular AC heater voltage.

And just had to look at the schematic since I stated the above.

Preamp tubes V1 and V2 have their heaters using DC. The DC heater voltage is getting pulled from one of the yellow wires. I would look to make sure all components associated with that circuit are ok. There appears to be a rectifier, a cap, two resistors and it specifically has a chassis ground as well as a signal ground. Make sure the grounds are making contact as well. A zener diode is being used in the circuit. I am guessing it is being used to regulate the voltage going through that side of the filament winding so it doesn't pull the other side too low, which would throw the AC heater voltages out of wack and could affect the DC heaters as well since it would allow more voltage to be drawn possibly.

The whole heater circuit is fuse protected, so if it pulls too much current the fuse should pop(As long as it is the correct fuse!) and you should have minimal damage hopefully.


It may be normal for the wires to get warm. If they are getting hot, say, to where you can't touch them, that is a concern. Heater circuits pull a fair amount of amps dependent on what tubes there are in the circuit. 4 6L6 and 4 12ax7s is somewhere around 5 amps for the heater circuit. Schematic calls for a 6.25A fuse.

[DonP]

EL34's pull way more current than 6L6 style tubes. Can be rough on the power tranny if it isn't designed for it. The extra heater current would pull down the available B+ and lower the power output.

[jgcable]

So... I biased it again and I found out why the bias was drifting. It was stupid me. I was playing through it while the bias probe was on. I didn't realize that as you push the tubes the bias changes. Once I stopped playing the bias stayed at 42mv. I let it run for about 2 hours with no issues.
The next day I turned it on again and was jamming on it. It sounds great. I was looking at the power tubes (5881's). I have 2 of them in it so its running at 50 watts. I noticed that one of the tubes didn't appear to be lighting up. The amp sounded great. The clean and gain channels worked and sounded perfectly with a ton of power. When I touched the tube it was cold. The amp was running on 1 power tube for about an hour at least. How could that be? Doesn't seem possible.
I think I know what I need to do. I need to remove that power tube board and hardwire all the leads on the left and the right instead of using those push in connectors. I have a feeling those inline sockets and pins are not making good connection. In either case.. I don't understand how the amp could be working with 1 tube only.

[DonP]

An amp will run with one tube, just not clean. The loop sided output would have a lot of clipping unless it was running Class A. If you are feeding it a lot of distortion you would have a hard time telling. If you like the sound play it as is and you have a 25W amp.

[cliffs_trip]

Did you take voltages across pins 7 and 2 of the sockets on the power tube board? Just to make sure it wasn't a tube with a bad filament? Out of all the things to go wrong on Crates, I've strangely never had an issue with the power tube board pins. Cold solder joints on the other hand ...

[jgcable]

Did you take voltages across pins 7 and 2 of the sockets on the power tube board? Just to make sure it wasn't a tube with a bad filament? Out of all the things to go wrong on Crates, I've strangely never had an issue with the power tube board pins. Cold solder joints on the other hand ...

The tubes are fine. I swapped them and the same side doesn't light. Here are more details.... The amp is 100 watts so it has 4 power tubes. I pulled 2 tubes and I am only running it at 50 watts. If I leave the inner 2 plugged in the right side doesn't light up. If I leave the outer 2 in the right side doesn't light up.
I believe the straight pin connector on the right side is responsible for the 2 right tubes and the 2 yellow bulbs for those tubes.
Here is the strangest thing of all... with only one tube working (believe me.. the other tube is COLD), the amp sounds exactly the same as it did with both tubes working. Its super loud and powerful and the clean channel is super clean and super powerful. It just doesn't make sense to me.

[DonP]

FYI, using a tube where the heater isn't working but hooked up to high voltage is like turning on an amp without letting it warm up first. Bad for the cold tube.

[cliffs_trip]

Makes sense now! The pins on those boards are small and can get dirty and bent easily to where they wont make contact. I own a BV120h and have worked on it several times in addition to several other Crate amps which use the same setup for the power tubes.

Were you able to trace the 6.3V all the way to the header where the power tube board plugs in(The connector side of the main board).

Will you be just stretching a couple of wires from pins 2 and 7 on the left side to pins 2 and 7 on the non working side? That seems it would be the fastest solution and would make it to where you could remove the power tube board. You may want to pull out or cut the pins which supply the heater from the connector if you do this.

[jgcable]

Makes sense now! The pins on those boards are small and can get dirty and bent easily to where they wont make contact. I own a BV120h and have worked on it several times in addition to several other Crate amps which use the same setup for the power tubes.

Were you able to trace the 6.3V all the way to the header where the power tube board plugs in(The connector side of the main board).

Will you be just stretching a couple of wires from pins 2 and 7 on the left side to pins 2 and 7 on the non working side? That seems it would be the fastest solution and would make it to where you could remove the power tube board. You may want to pull out or cut the pins which supply the heater from the connector if you do this.

FIXED!!!! I took the amp apart and I pushed down on the tube board while the amp was running on 1 tube only and sure enough... the tube lit up.
I then loosened the screws and seated it and reseated it a few times and I tightened the screws up securely. Amp is running great.
What a crappy stupid design. If they had only used ribbon connectors instead of those inline pc mounted connectors I bet most of the Blue Voodoo's that crapped out would still be running. If it happens again I will just do the flying lead mod.

I will say one thing that I mentioned when I first got this amp. This amp sounds pretty frikkin good. The clean channel is very nice and the gain channel can absolutely handle just about any genre of rock and metal.

[DonP]

Does the amp sound better or worse with push pull (2 or 4 tubes) working?

Louder?