my valve amp gave me a stroke...

[Keven]

Hey guys

yesterday at band practice my valve amp (a traynor YCS100H with 4 el34's) gave me a heart attack

everything is done as usual, i go down to the practice room, turn standby on, go back upstairs, chat with drummer, plan and plot and everything. about 40 minutes later, i go back down, turn on the power, the third valve from the left glows deep blue, then bright blue... then goes to a deep red. i turn everything off, wait for like 2-3 minutes. turn on the standby, and then turn on the power to the valves.... works like a charm. played all night with it, no problem

 there's a leeetle blue glow but nothing bad. my el84 in my valve junior amp has a much worst blue tint and it still works and sounds good.

something happened while sending the high tension to the valve? just a jitter? did my amp just scream ''retube me!''

what just happened? should i expect a tube meltdown the next time i turn it on?

this is while running the amp with the 30w Triode mode, not sure if that helps.

conclusion?

[Frank]

Happens a lot, probably harmless, good explanation here

[Frank]

also, disregard the stuff about mercury vapour tubes

unless you have these inside your amp

http://www.youtube.com/watch?v=Rt-a8fxgtno

[Keven]

and what about the increasing luminosity going to red? i'm a wuss, but i looked like it was getting hotter and hotter and could've died if i hadn't turned the power off... but then, it should have done the same thing anyway even when i turned it back on, and it didn't...

[Frank]

hmmm, that's not good, are the plates glowing red or is the blue glow turning red?

[Keven]

the blue glow was getting brighter, from a normal blue, to bright blue, to white, then red. then i turned it off, turned it on, and jammed for the rest of the evening and it was fine, same tone as always too. i don't dime the amp i rely on pedals to get my dirt and run the amp fairly clean. it was just one valve too. the plates are a normal color, but from what i remember (it went by very fast...) i could see them turning red as the tube was getting hotter in terms of seconds.

[Frank]

Well first I'll make the usual disclaimer about not being able to diagnose the amp reliably without seeing it.

I can't really diagnose the amp reliably without seeing it.

Though from what you're describing, it's just normal tube glow and I'd guess the change in colour is simply due to the tube heating up.

If your amp is severely underbiased then sometimes an excessive current can run through the valve(s). Sometimes this creates a bright red hot spot which spreads until the whole plate is glowing red hot although often the HT fuse will blow before it gets that bad. I've seen this happen when idiots put 6L6 tubes into amps designed for EL34 without rebiasing.

If you see any metal valve component other than the filaments (heaters) glowing red hot then switch off immediately and get the bias checked. Remember excessive plate current means excessive current in your output transformer and those ain't cheap to replace.

edit: Youtube it! Valve glow is a lovely thing to see. And it would help people here to diagnose your amp!

[Keven]

it did it only once and then worked fine. that's the thing, i wouldn't know how to reproduce it as the amp simply does not move from our rehearsal spot. i just turned it on and it threw this at me :P

i appreciate the wisdom however and it's good to know that it won't kill my amp yet, but new valves are gonna be needed soon.

[Frank]

It's not uncommon but it is disconcerting the first time people notice it. I've seen glow outside of the tubes in badly set up amps as well, that looks very strange. The science people say it's ionisation, I'm happy to take their word for it. So with the usual disclaimer still in place, I'll say you can safely ignore it unless the plates start heating in which case it's time to take the amp to see the doctor.

[Supernaught]

Did you mean to say that you turned the standby on, then the power?     If so thats not going to do your tubes any good at all.     I assume you meant the other way round, so ignore me :)

[HTH AMPS]

hmm, just the one valve glowing red.   its obviously pulling way too much current for that to happen, but now its working fine.  so, its either a problem with the bias supply (if its a fixed bias amp) or more likely just a valve on its way out.

either way, take it to a tech and get some new valves.

[Keven]

to rephrase. i turned the heater power suppler on, then before going to play, hit the switch for the HT.

i think it's a cathode biased amp. it's a 4x EL34 100w amp. there's a bias trimpot at the back.

a customer at my shop had the same amp with the same stock ElectroHarmonix tubes and the same thing happened, his was still under the 3 month valve warranty so traynor just swapped the tubes for another quad and rebiased. on my end though, i'll just dish out for a quad of winged c's and be done with my problems :D

[jpfamps]

A small about of blue glow in a valve is perfectly normal, both within the plate structure and inside the envelope where stray electrons strike the glass.

If the plates in a valve glow red it is drawing too much current and the amp should be switched off.

The most common cause of "red plating" is loss of bias supply to the valve. If the fault is intermittent it could well be that the valve's grid pin in making poor contact with the valve base, and the socket may need retentioning. This was a real problem with JJ-valves a few years ago when they decided to use thinner pins than other valves.

Additionally, excessive blue glow in valve envelope can be a sign of too much gas in the envelope. Too much gas in the envelope can cause grid current which will bias the valve hotter and can lead to thermal runaway.

I've also seen thermal runaway in several new JJ valves, the cause of which we never really established as the valves tested fine for gas.

[HTH AMPS]

it could well be that the valve's grid pin in making poor contact with the valve base, and the socket may need retentioning. This was a real problem with JJ-valves a few years ago when they decided to use thinner pins than other valves.

I remember this being the case when JJ first released their KT77s.  I complained about it to the place I got them from as he'd obviously known about this from the reaction he gave.  I was told that it was 'simply' a matter of retentioning all of the octal valve base sockets ($%&# that).  In the end I returned them, got a refund and bought some winged=C= EL34s from somewhere else.

[Keven]

Well, an update. it turns out the tube was red plating. so i swapped it to another socket. still redplating, and alot of hum. it forced me to pull out two tubes and set my amp's impedance to half the cabinet impedance since i had no spare. i should've done this along time ago! this amp now sounds awesome, it used to be too bottom heavy, but pulling out two power tubes just fixed everything! and as a bonus, it'll cost me much less to replace the power tubes now :D

now, this amp has a 'triode' mode that sets it for 30W ''class A'' instead of 100W class AB. setting it in 30W mode is the only way i can get it to run at half the cabinet impedance, and now, since i have two tubes out, i must be close to 18 watts or something :D