#1
I just fired up my Valveking 100 head and it immediatly made a few popping sounds, so I turned it off. After a minute I turned it on again and it didn't pop, but I noticed that the right 2 power tubes were glowing blue whilst the other 2 power tubes had their normal orange glow. After a while it made another popping noise and the blue glow was gone. I played for a while and everything seems fine again..
The amp does buzz and sometimes hiss a bit more since a few months, compared to before. I already switched out V1 and V2, but that made no difference to the buzzing and hissing.

Is this a sign that I need some new power tubes or is it something else? I read it could also be the phase inverter tube?
#2
Umm, if the power tubes were different than they normally are and you're having issues I would try swapping out the power tubes first. . . .

It's always a good idea to have a spare set so if you don't have a spare set this is a really good opportunity.

The power tubes have a finite life anyway.
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#4
The power tubes are probably on their way out. Being blue means nothing though, that's just impurities in the plate flourescing. That's normal.
Phase inverters do tend to wear out faster than the other 9 pin tubes but my money is on the power tubes themselves. Can't hurt to try your spare in the phase inverter though just to be sure before you lash out on power tubes.
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Cathbard Amplification
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#5
Thanks for the replies.

About the blue glow; this is the first time I saw that, normally the tubes are just orange-ish. It did seem to have a direct connection to the extra humming and popping noises (or it was a coinsidence), when I turned on the amp the hum became louder when two of the tubes became brighter blue (or perhaps it was purple, I don't know) and after one of the popping noises the blue glow was immediatly gone in both of the tubes and the amp went back to it's normal noises.
The glow kind of looked like this, but only in the right two tubes. The left two were normal:


I just came home from work and switched the amp on again and all seems fine. I find this makes it hard to find the cause. If the amp was doing it constantly I could just try things till something makes it stop, but it's not that easy now.

I'll try to replace the PI tube in the hopes that the extra humming/hissing of the last few months goes away, but I'm also not sure if that extra humming/hissing is in any way connected to what happened yesterday.
Last edited by Pizza123 at Oct 7, 2014,
#6
The amp has been running fine for 10 days now, with a bandpractice included. So I'm still not sure what's wrong (if anything is actually wrong).

I did find out something new though; When I turn the texture knob towards simulated class A the noise increases quite a bit, though there's also some noise at class AB. But, when I keep the knob at around 4 o'clock (just a bit before the knobs' endposition at class AB) the noise is gone. Does that make things any clearer for anyone as to what's wrong?
#7
Replace V3.
Gilchrist custom
Yamaha SBG500
Telecasters
Randall RM100 & RM20
Marshall JTM45 clone
Marshall JCM900 4102 (modded)
Marshall 18W clone
Fender 5F1 Champ clone
Atomic Amplifire
Marshall 1960A
Boss GT-100


Cathbard Amplification
My band
#8
Just tried replacing V3, didn't make a difference to the noises unfortunatly. But perhaps this will make sure that the tubes don't turn blue and make popping noises again.

The noise I'm getting now (since that last few months) is kind of what you hear when you're talking to someone on the phone and he's standing in the wind. Kind of this uneven crackling noise. Could the textureknob circuit be damaged?

I should also mention that the amp isn't 100% original anymore. I'm not sure what has been changed exactly, but the previous owner told me that he had a mod done to get a hotter bias to the powertubes. The outside of the amp looks untouched, so it doesn't seem to be the popular biaspot mod.
#9
A blue glow on power tubes is 100% normal and nothing to worry about.
Change the power tubes and see if it changes.
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#10
The texture knob is very simple. It is connected to the tail of V3b. If replacing the tube didn't do the trick, I'd be replacing the pot itself. It still could be the power tubes, not because they're blue, that's normal, but because it's the only other thing that could be affected by the texture control. The pot is cheaper, well it is if you are capable of changing it yourself.
Gilchrist custom
Yamaha SBG500
Telecasters
Randall RM100 & RM20
Marshall JTM45 clone
Marshall JCM900 4102 (modded)
Marshall 18W clone
Fender 5F1 Champ clone
Atomic Amplifire
Marshall 1960A
Boss GT-100


Cathbard Amplification
My band
Last edited by Cathbard at Oct 17, 2014,
#11
Thanks again. I decided to wait till after tomorrow before trying new stuff out, as I have a gig tomorrow. But it just popped again whilst I was playing, with blue and now also red glow from the middle of the powertubes. The tone lost a lot of low end and the amp was louder. There was also a slight burning smell. Just to confirm before I place and blow up a new set of powertubes, the burning smell could come from the busted tubes, right?
#12
yes it could have been the tubes. Sounds like they red-plated on you. Did the amp shut off or just a bad noise?

If the amp turned off, you may need to replace the fuse(s) in the amp.
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Morley Bad Horsie 2
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#13
The amp still works, so the fuses are alright. I looked up some images of red-plating, and yes, that's exactly what it was.

I'll see if the tubes are cold enough now to replace 'em.
#14
Yeah you should be fine then. put the new tubes in and you should be good. you really need to rebias the amp, but it isn't going to kill the amp if you don't.

Throw the bad tube away, and keep the other for an emergency spare. That way if anything similar ever happens you can put that one in to get through a gig.
2002 PRS CE22
2013 G&L ASAT Deluxe
2009 Epiphone G-400 (SH-4)
Marshall JCM2000 DSL100
Krank 1980 Jr 20watt
Krank Rev 4x12 (eminence V12)
GFS Greenie/Digitech Bad Monkey
Morley Bad Horsie 2
MXR Smart Gate
#15
Thanks again Robb. Fitted the new tubes and so far so good. The Valveking has a non adjustable fixed bias, so I'm alright in that regard.
#16
2002 PRS CE22
2013 G&L ASAT Deluxe
2009 Epiphone G-400 (SH-4)
Marshall JCM2000 DSL100
Krank 1980 Jr 20watt
Krank Rev 4x12 (eminence V12)
GFS Greenie/Digitech Bad Monkey
Morley Bad Horsie 2
MXR Smart Gate