Orange 200 thunderverb - tube failure

[überfuzz]

Hi!

A friend of mine has a Orange Thunderverb 200. Situation: one or two tubes started to glow, blueish and sort of vent south, a quad of KT88s. (This is would be my friend describing the event.) He vent an bought a quad of 6550, don't know which brand but I think it is TADs. Now the Orange vendor here tells him to get it up on their desk so that they can tinker with it and hefty charge him. Changing tubes is a delicate matter, something else can be wrong etc. I tell him that there's probably noting wrong more then funky tubes. Further, that we can pop the new tubes in the amp next time we get together.

So, now I wonder if anyone here has tinkered with an Orange thunderverb 200. How did you set the bias, that is with 6550s. Anything else I should check while I'm at it?

Cheers!

[nosaj]

Just my 2 cents but popping in a new set of tubes is like popping in a new fuse without looking at the issue. Nobody can sguess what you'll find when you look at it. So just look at it like any other amp. Pull your data then compare with your measurements.
Anything else you should check? Use sight and smell then let us know what is found .

nosaj

[Mick Bailey]

A tube that starts to glow blueish can indicate a gradual loss of vacuum - 'going soft', which can end up being a shorted tube. You say "one or two" started to glow. One I can understand. Two may point to someting else wrong. Do any of the tubes have a white edge to the gettering, or have any gone completely white?

If you get a failed tube you always need to check associated components - screen resistors and tube socket especially.

[J M Fahey]

Situation: one or two tubes started to glow, blueish and sort of vent south, a quad of KT88s.

What does this mean, in English?

the Orange vendor here tells him to get it up on their desk so that they can tinker with it and hefty charge him. Changing tubes is a delicate matter, something else can be wrong etc.

"Tinker"?
"hefty charge him"?
Ok, how much does he want to pay?
What kind of service does he expect?

something else can be wrong
well , of course.
Out of the top of my head, those symptoms may indicate loss of bias ... which will *nuke* the next tubes you plug in there.

Plus I don't understand how he decides to change tube type for some unknown reason and expect not to rebias

Of course, there is some chance he just plugs those tubes there and the amp works reasonably well.
Say, 30% chance, not bad.

I prefer to bet at the Poker table, but, hey, that's me.

[Gtr_tech]

A tube that starts to glow blueish can indicate a gradual loss of vacuum - 'going soft', which can end up being a shorted tube. You say "one or two" started to glow. One I can understand. Two may point to someting else wrong. Do any of the tubes have a white edge to the gettering, or have any gone completely white?

If you get a failed tube you always need to check associated components - screen resistors and tube socket especially.

No, the blue glow is normal. A pink glow indicates a gassy tube.

[Mick Bailey]

A localised flourescent blue glow is normal for power tubes, agreed.

A diffused bluish-white glow (particularly inside the electrode assembly) would be suspicious to me if it suddenly developed in an older or well-used tube. This can be a precursor to a bright pink glow - 'time for bed' - lots of gas bombardment and potential for a short.

[Gtr_tech]

As far as this amp goes, information such as plate supply voltage and output section configuration should be brought to the table before any further advice can be given. If the amp was spec'd for a KT88, I would be leary sticking today's "6550" in there. The old USA made GE 6550A would work great, but that ain't what we have available.

Maybe these would be a good choice (no personal experience):
JJ KT88 Power Vacuum Tube

Or if you want a super durable tube, I just found this new addition to the big and burly game:
Tung-Sol KT120 Power Vacuum Tube

A very interesting tube there. 60w plate? Oh mahn....if they are built well, SVTs would love those.

[Gtr_tech]

http://www.tungsol.com/tungsol/specs...ecs-curves.pdf

Yowza....forget all the 6550 variants. This one looks like a winner.

[Mick Bailey]

That's a real find. I'm just thinking of how that would make a pretty neat SE amp.

[überfuzz]

As far as this amp goes, information such as plate supply voltage and output section configuration should be brought to the table before any further advice can be given. If the amp was spec'd for a KT88, I would be leary sticking today's "6550" in there. The old USA made GE 6550A would work great, but that ain't what we have available.

Maybe these would be a good choice (no personal experience):
JJ KT88 Power Vacuum Tube

Or if you want a super durable tube, I just found this new addition to the big and burly game:
Tung-Sol KT120 Power Vacuum Tube

A very interesting tube there. 60w plate? Oh mahn....if they are built well, SVTs would love those.

Spot on dude, this was what I said to the fella asking me about his Thunderverb 200. I asked him to get a schematics or similar so that we could check basic things. Looking for busted components etc.


Anyone knows the rated plate voltage the power section of a Thunderverb?