Fireworks

ICBM

A bit late for fireworks night, but I took these pics a few days ago…

This is what happens when a valve gets enough air in it to produce a self-sustaining arc, just like a neon bulb. I think the pink colour is caused by the Argon in the atmosphere, but I could be wrong.

Apologies for the camera shake, I was trying to flip the standby switch on and off for just long enough to get the pics without blowing anything else!

http://i.imgur.com/iozVyu4.jpg

http://i.imgur.com/DMDme29.jpg

The croc clips across the HT fuse holder are going to a current meter - I didn't bother trying to get an accurate reading but it was well over 500mA, which at the roughly 350V HT in this amp makes the arc at least 200W. You definitely don't want that for more than a second or so, or it will fry the mains transformer if the main fuse doesn't blow quickly enough.

ecc83

We had a really good video of a KT88 going into "Purple Death".

This was induced by an ever increasing heater voltage (IIRC it blew at about 25volts!) . HT was about 600+ and a 1A T fuse was made very black.

I shall have a chat and see if anyone still has the vid on file.

Dave.

jpfamps

Argon would a good bet, as it relatively abundant in the atmosphere (around 1% I think), and will not react with the getter.

martinw

I'd be surprised if that's the Argon. Usually air leaks in vacuum vessels result in a red (nitrogen) plasma. I suspect there's more than just a straight plasma going on in there!

ICBM

It is the exact colour of an Argon light though…

http://upload.wikimedia.org/wikipedia/commons/8/87/Argon_discharge_tube.jpg

I'm sure you've seen it too, and it's always that same colour.

ThePrettyDamned

I'm going to say that's argon, but it's been a couple of years since I last worked in a physical chemistry lab...

Whatever it is, it's cool! When my el84 blew up in the mooer, initially, the amp started sounding louder or... Something. I mean, seriously, great for a few seconds, louder, prouder, and better. Then it'd go back for a mo, then it glowed bright blue, then white then dead. Woops! I vaguely remember a popping sound, which might suggest it was no longer a vacuum by that point.

Luckily, only the valve went and swapping a new one in fixed everything.

jpfamps

My argument for it being argon, other than the colour of the discharge, is that if air gets into the envelope both the nitrogen and oxygen in the air will react with the barium in the getter (assuming the getter has not be exhausted, which would not appear to be the case here).

Argon (1% of air, so significant) won't, so will remain the envelope.

martinw

Yeah, kind of, but anyway the fact remains, you can't select a gas to make a plasma with. There's a lot more nitrogen than argon in air, and if argon can get in, so can nitrogen. You can't get an argon plasma from an air leak.

I'd bet there's some fairly complex chemistry going on in there with that hot metal. With a pure plasma it's just voltage and gas particles. Also, the more light emitted, the more the colour moves towards white, and pink can easily be mistaken for purple. A pure argon plasma is purple...very distinctive, like the ends of the pic above.

Dave_Mc

Are you sure that's argon? It looks more like Bugeron to me...

martinw

Dave_Mc said:

Are you sure that's argon? It looks more like Bugeron to me...

Just about to transition into Melton....

jpfamps

martinw said:

Yeah, kind of, but anyway the fact remains, you can't select a gas to make a plasma with. There's a lot more nitrogen than argon in air, and if argon can get in, so can nitrogen. You can't get an argon plasma from an air leak.

I'd bet there's some fairly complex chemistry going on in there with that hot metal. With a pure plasma it's just voltage and gas particles. Also, the more light emitted, the more the colour moves towards white, and pink can easily be mistaken for purple. A pure argon plasma is purple...very distinctive, like the ends of the pic above.

You may well be correct, however there is a mechanism whereby nitrogen is removed from the vacuum inside the valve envelope by reaction with the barium getter to form barium nitride.

By contrast, argon does not react with barium (or indeed anything else), so won't be removed from the valve envelope/

ICBM

martinw said:

Dave_Mc said:

Are you sure that's argon? It looks more like Bugeron to me...

Just about to transition into Melton....

Melton is more commonly produced by bias failure, so the fuse doesn't blow immediately.

http://imgur.com/Ufd4Zjh.jpg

Dave_Mc

)

Actually now I think of it, bugeron is more of a yellow, flame colour

martinw

ICBM said:

martinw said:

Dave_Mc said:

Are you sure that's argon? It looks more like Bugeron to me...

Just about to transition into Melton....

Melton is more commonly produced by bias failure, so the fuse doesn't blow immediately.

http://theangelconversations.com/pics/MeltedEL34s.jpg

I had a pair like that a couple of months back, caused by bias failure on a TSL.

ICBM

martinw said:

I had a pair like that a couple of months back, caused by bias failure on a TSL.

Those came out of a DSL.

jpfamps

Mine came out of a Hiwatt.

http://jpfamps.com/do-you-think-this-valve-has-overheated

ICBM

More fireworks…

This is a Fender Eric Clapton Twinolux which wanted to be a roman candle.

http://i.imgur.com/AKz8WPm.jpg

http://i.imgur.com/rBhxT0u.jpg

http://i.imgur.com/muTTizz.jpg

http://i.imgur.com/sip7YFK.jpg

Some serious temperature has been generated there! That's a ceramic valve socket which has actually vitrified by melting the metal terminal into itself - the little shiny blue-grey 'glazed' spot nearest the camera in the last pic - by arcing between the plate and filament pins. I thought ceramics were supposed to be superior because they don't do this. Ho hum…

(For the other techs) Stupid amp design too - it has filament fuses (unnecessary really, and not blown) for both the main and rectifier filament secondaries, but no HT fuse… which might have prevented this or at least limited the damage. I may rewire it to make one of them a HT fuse since I'll have to replace a fair bit of the wiring anyway.

It smells expensive.

ChrisMusic

I have to say that I am really enjoying this thread.  I assumed when I picked a guitar up again recently that valves would be passé or just niche.  I had a good few valve amps in my past life, but never really new that much about them, so I've made up for lost time with all the sage and interesting discussions on here.  Fascinating stuff, and I love the pyrotechnics too.  Thanks chaps.

ThePrettyDamned

Wow, that's a £2000 amp that's...Surely not that old? What the hell happened?!

jpfamps

ThePrettyDamned said:

Wow, that's a £2000 amp that's...Surely not that old? What the hell happened?!

This was caused by a valve failing by an internal short; nothing to do with the quality of the amp, although as ICBM points out an HT fuse would almost certainly have limited the damage.

ThePrettyDamned

jpfamps said:

ThePrettyDamned said:

Wow, that's a £2000 amp that's...Surely not that old? What the hell happened?!

This was caused by a valve failing by an internal short; nothing to do with the quality of the amp, although as ICBM points out an HT fuse would almost certainly have limited the damage.

Phew.  I'd be so upset otherwise!

Edit: I wish I understood this speak so I'd have some idea of these things! Pretty scary that a simple valve failure can do that kind of damage though...