Blue light and slight buzz; problems ahead?

[aowron]

Last night after jamming for a while, I started hearing a slight buzzing from my amp (did though first hear it when we took a shorter break) and the EL34s had a blueish light. When I put the amp into standby, the buzzing and blue light disappeared. After letting it stay powered off for a while and later powering it up again, the blue light disappeared and it was possible to use the amp without any issue.

So, could this be sign of the tubes either having the wrong bias (which doesn't surprise me, the guy who had it before had just popped in EL34:s instead of 6L6:s and flipped the 6L6->EL34 switch on the back of the amp) or reaching the end of their lifespan?

Also, if a tube gives up, could that potentially fuck up the transformers in the amp or would a fuse pop before that happens?

[Hemisaurus]

Ask technical questions in the technical question section, better response time.

Is it like an electric blue or a more purplish blue?



This is a healthy glow, if you're getting something blue and like lightning, arcing, then you've got bad tubes already.

If a tube goes, it has the potential to fuck up many things, screen resistors etc. a transformer might be an extreme case, but it's possible if you left it running a while. Some circuits will have a safety fuse, some may not.

Putting your amp in standby cuts off the plate voltage and just leaves the heaters energised, so yes that would make any glow go away.

If it hasn't been rebiased, go get it done, especially if it's got a bias testpoint, it's so easy, what model is it?

[VOLVO)))]

Sounds like a Boogie or an Ampeg VL1002/502.

The Mesa has fixed bias...

[RacerX]

I think he runs a Laney.

[Hemisaurus]

Peavey and Bugera both have EL34/6L6 switch too, Bugera has an external bias point, you need an RCA phono jack and a meter, it's that simple.

I could deviate into a long bias diatribe here, but the upshot it, yes things will run when incorrectly biased, but they may not run well, and they may not run for long, I believe the Van-Halen brown sound was achieved at the expense of a retube of the amp every show. He'd have been cheaper just buying a Dano power supply with voltage sag. 

[El Zombre]

I could deviate into a long bias diatribe here, but the upshot it, yes things will run when incorrectly biased, but they may not run well, and they may not run for long, I believe the Van-Halen brown sound was achieved at the expense of a retube of the amp every show. He'd have been cheaper just buying a Dano power supply with voltage sag.  

A bit off topic, but I thought the "definitive" answer made the rounds a year or so again, w/ EVH basically saying he got the tone by using a Fender Bassman as a preamp for his Marshall. Like taking direct out (or even speaker out   ?!?) from the Bassman and plugging it into the Marshall.

Found a source , but it also wasn't at all what I claimed it was: http://books.google.com/books?id=DL3I9qQWdeAC&lpg=PA220&ots=AcQqXDVWCQ&dq=Van%20Halen%20bassman%20marshall&pg=PA220#v=onepage&q=Van%20Halen%20bassman%20marshall&f=false

[Hemisaurus]

hence he might have sounded better using a Dano

[RacerX]

This Aowron dude runs a Laney.

[dunwichamps]

buzzing is a bad sign, glow is okay, arcing internally is bad. Best bet is to open the back panel, then play the amp loud while someone watches the output tubes, under low light if you see any blue spark arcing then the screens are failing/about to fail and new tubes are needed pronto!!!!

[aowron]

Thanks for the answers guys. The amp is indeed a Laney (a GH50L).

It has a fixed biased, though the bias adjustment pot is somewhere on the PCB; looks like they intentionally made it a bitch to bias.

Anyway, the blue glow was electric blue. After leaving the amp unpowered for a while, the tubes lighted up as normal, and when checking the tubes while repeatedly striking a powerchord, nothing out of the ordinary could be seen (that blue glow couldn't be seen, guess my bandmate who was watching the tubes would have noticed lightning arcs). Also, the amp didn't buzz after it had been turned off for a while.

Well, I suppose I should go get it rebiased, might aswell get the EL34:s replaced with KT77:s while I'm at it.

[aowron]

Checked the tubes today; after a few minutes of playing, it almost looked like there was some kind of blue "fluff" (or mold) on the inside of the shield thingy in the tube. Is that a tube arcing? Took a few pictures too, though wasn't able to get any good picture of the "fluff".

[Hemisaurus]

Fluff sounds more like a hard-working tube haze, as shown in the above pic?

You can get a haze on brand new tubes, it doesn't mean a thing.

Arcing is like sparks or lighting in your tube.

If it's developed a hum, it could be a bad preamp tube more than a bad set of power tubes, you could try swapping your preamp tubes around (mark them first so you can put them back where they came from), if the hum changes in volume, it's a preamp tube. Basically if V1 is bad, and you move it to V2 the hum should get quieter, as the hum is now further along the amp stage. If the hum is in V2 and you move it to V1, it will get louder, etc.

I'd wonder about the driver tube, if you've changed the tube type, it would be the last dual triode before the power tubes, so V3 in a 3 tube preamp.

[aowron]

So would the sparks/lightning arcs be clearly visible? The blue glow didn't look like what it looked like on the images, it was more fluffy, though since it was behind that shield thing in the EL34:s, it was pretty hard to see it.

I have attached a couple of pictures of the power tubes. The first one shows the blueish glow (though not really clearly).

I'll try and check if I can hear the hum again; I have though only heard it once so far.

Isn't the first tube in the GH series the driver tubes? I believe it looked like that in some simplified schematic I found in the Laney GH*L manual.

Swapping the preamp tubes would probably be something worth doing even if they aren't bad; currently using some boring Sovteks (well, should be Sovteks according to the guy who sold me the amp).


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[Chovie D]

i dont see any blue glow in your pics.

you can take a pencil, use the eraser end, and lighty tap on your preamp tubes while the amp is on and your guitar is plugged in.
If it makes a noise when tapped, could be a problem.

[VOLVO)))]

i dont see any blue glow in your pics.

you can take a pencil, use the eraser end, and lighty tap on your preamp tubes while the amp is on and your guitar is plugged in.
If it makes a noise when tapped, it is microphonic.

[Chovie D]

and microphonic is a problem 

couldnt it be an indicator of other problems with the tube as well?
even reseating the tube can sometimes help it seem slike

discalimer: i dont know shit