Crate Blue Voodoo 2612 smelled funny then not working right

[DreamTheater]

I just picked up a 2612 BV combo for 120.00 Took it home and tested it out and seemed to be working properly for about 3 minutes. I then noticed a smell that seemed to be electrical. I did not notice any smoke. The smell was quite strong though. Suddenly the distortion level went way down and sounded almost thin and weak.
Also a significant reduction in output level occurred. The preamp tubes did have an Orange color glow and the power tubes had an incredible Purple glow. I was operating the unit at a high level when the reduction took place. I have plugged my guitar directly into the effects return jack and I do in fact get what I believe to be full output through both speakers. Plugging into the actual instrument jack though still results in the odd response.
I failed to say that I did replace both 6L6 power tubes prier to doing the effects return jack test so I don't know for sure if the amp would have responded the same with the original tubes that were being used at the time of the failure. Anyone have an idea for a safe,simple and inexpensive fix.

[guitardad]

Were any components over heating?

If you jumper the fx loop with a guitar cable or patch cable does the sound still die out? If not, check the connections on the fx loop return jack or you may just have to replace it. Sometimes it is fractured solder at the jack pin or can be the jack itself. Some can be cleaned with Deoxit spray. On most fx loop or Inst jacks, I never trust just cleaning them. I opt to replace them.

Tubes should not glow reddish orange. If they do and have weak output, the tubes are likely "red plating" due to loss of bias. At times bad output tubes may red plate or at least appear to.

[km6xz]

He said the preamp tubes had an orange glow, just as would be expected in a normal amp. The power tubes with a purple glow is another matter. Is the glow faint color tint or bright? In either case, do not turn it on until you figure out a reasonable plan of attack on determing the problem because you risk ruining more expensive things if you continue to run a malfunctioning amp.

If you have any test equipment let us know.
Make sure the fuses are their correct rating. If someone was having problems before selling it and it blew fuses, they likely put in fuses that were higher rating to get it working again. That would mean if there is a reason for the normal fuse to blow, a larger fuse would allow real damage to occur with continued operation.

If you have another amp, try pulling the output tubes and run a cable between the effects line out and plug it into the return line on the second amplifier. That will allow you to determine if the problem in in the preamp or power amp section of the amp. Does it overheat or smell with the power tubes pulled out? If it does, remove the chassis from the cabinet and see what is overheating. Your nose will be very sensitive to warm air currents and detecting the area from which the smell is coming from.

Before delving into anything more complex, let us know what test instruments you have: DMM, scope, signal generator, dummy load, lightbulb limiter etc.

[oc disorder]

DreamTheatre ..firstly is that a typo "2612" perhaps it should be 6212 I presume a Crate BV60 ?
My take on what you posted is that with the new tubes no purple glow and the amp seems good when plugged into effects loop return although without pre-amp its very low volume but appears to have full sound . If this is the case it's highly likely the pre-amp section has a fault ...
The first component I would check is a 47 ohm (Yellow Violet Black) resistor marked R105 that feeds the switching transistors and the leds in the LDR switching do-dackies !
I also suggest replying to Km6xz first..and seriously also consider at this stage if you should take it to someone familiar with this type of repair.
It's a major call for an initial repair project but we all commenced somewhere usually with low voltage projects that are less likely to be lethal apart from Steve who enjoys lighting up his Tesla coils !

[DreamTheater]

Thanks for your responses. to answer GuitarDads question---yes I did jumper the effects loop with a short instrument cable and the result was still very weak distortion and possibly even less output (I did not run the master volume very high during this test).
Replying to Km6xz---The only test equipment I have is a lightbulb continuity tester. I don't know what size fuse is supposed to be used (I will research). I do not have another amp to to do the test so that is not an option at this time. The smell only occurred during my initial testing of the unit when I was operating it at a high level. I have not noticed the smell since. I have not removed the chassis from the cabinet enclosure as I was concerned about safety. I would like to remove the chassis and visually inspect the internal components such as fuses, burnt resistors etc. but don't know what I should be concerned with as far as safety. I know that caps can store voltage and that I should not touch them while they still have a charge but would simply changing the fuses pose a shock risk to me?
As for oc disorder---You are correct, the amp is a Blue Voodoo 6212 2x12 combo with the blue (not black) tolex. It uses two 6L6 power tubes and 5 preamp tubes. I believe that one of those preamp tube might be a 12ua7 while the other 4 are 12ax7. Plugging into the effects loop return with the output of a stand alone ss guitar preamp yielded full volume and full output and sounded pretty good actually. I would like to pull the chassis and inspect but I need to be sure that changing fuses is safe etc. Any additional comments you may have for me after reading this additional information would be greatly appreciated. Thanks.

[km6xz]

OK, that helps a lot. If the power amp works well with an external signal going into the effects return the worries about damaging something and the possibility of an incorrect fuse are greatly diminished.
The preamp used a lot of light dependent resistors for switching channels and paths so it can appear complicated.
If you have a known good 12AX7 try substituting the 12AU7 since all 4 miniature tubes are supposed to be a 12AX7.
If you do not have a good 12AX7 to swap in, try using the 12AU7 in the first socket. and see if that helps.

Here is a link to download the service information for the BV60h
http://elektrotanya.com/crate_blue-v.../download.html


Scroll down the page to see the "Get Manual" is small text.

I tried to attach the file but it does not appear so I edited the post to include the link above

[DreamTheater]

I have a supposedly new 12au7 still in the box (although the box is opened). Which tube of the 5 preamp tubes would be the 12au7. Looking at the backside of the amp...there are 5 preamp tubes that run from left to right. Four of those tubes are basically in a close group while the 5th tube is off to the right by itself. I would think that that 5th tube would be the 12au7 although I see that 3rd tube from the left is actually a 12au7 and I believe that the original owner may have replaced that tube in that position when maybe that 3rd tube should have been a 12ax7. He gave me 2 extra 6L6 power tubes a single 12au7. I know for sure that the 3rd tube is a 12au7 because I can clearly see it spelled out on the tube itself. The other 4 tubes have no markings on them so I really cant be sure that they are 12ax7. I tried to attach a photo but cant seem to get it to attach

[km6xz]

The schematic I saw might not be the correct one because it shows only 4 12AX7s and 2 6L6 tubes. The difference between the 12AX7 and 12AU7 is the former is a high gain dual triode and the latter is a low gain dual triode.
The 4th tube socket from the input jack is where the 12AU7 belongs

[DreamTheater]

Alright...thanks. currently the 12au7 resides in the 3rd socket from the input jack. I will switch out and see what happens.

[Jazz P Bass]

Yeah, V4 is the reverb tube.
It should be a 12AU7.

[DreamTheater]

I switched the tubes around so that v4 was 12au7 and the sound was rather poor. I then replaced the 12au7 with an alleged new 12au7 and the sound seemed improved. Now here's the strange thing.....when I turn the reverb knob up I would expect to hear reverb introduced into the audio, but what I get instead is some type of nasty distortion sound...no reverb at all...only nasty. Can I remove the reverb tank completely without worry and just tape off the rca plugs that plug into the tank. I intend to use time based effects in the loop anyway. My other concern is that smell that occurred when I first fired the amp up. The smell has not returned but is it possible that some internal component fried and even though the amp seems to be working, it might not be working properly.

[Jazz P Bass]

Thouight I should edit my above post :"Yeah, V4 is the reverb tube. It should be a 12AU7."
V4B is the reverb send.
V3A is the reverb return.
V4A is the dry/ reverb mixer.
The fact that the reverb is not working may be a hint.
As to the smell, that could be anything.
I really do not see this amp getting repaired if you do not have at least a simple volt meter.
Can you get one?

[DreamTheater]

very frustrated now...I just discovered that one of the speakers is shot.

[DreamTheater]

This is my first tube amp and was hoping for better. I spent $120.00 on it and thought I was getting a great deal. Now it seems like a piece of junk. I could put a couple new speakers in it and bring this amp into a tech. I don't know what the tech would charge. Really don't want to put tons of money into it. Is it worth trying to make something out of it or do you think that its a sinking ship.

[DreamTheater]

Kind of funny now...I was getting some scratchy sound out of one of the speakers (thought it was in the cab itself) so I removed both from the cab and made up a long speaker cable. Placed both speakers on the floor wired in parallel as they should be and was able determine which speaker it was. I was gently pushing the cone down and releasing it when I heard a physical grinding with each depression. After doing this pressing and releasing several times, the grinding was gone and the cone seemed to move freely with each compression. Not sure what to make of it. Gonna hook them back up and see what I get.