I think i Blew a Tube....

You probably did blow it. Get it replaced, and be nice to it. You may need to get it checked out by a tech to make sure you didn't fry something else near that tube.

 

That sounds like there is short between the heater filament and the plates internally. Get that tube out of there immediately before it damages your amp!

 

nice cab btw

 

torn speaker cone maybe?

 

FWIW:

read through this thread the other day and had a question but was wanting to wait till it lost gas to take it on a tangent.

1) Was wondering what part of MB's description led to that diagnosis and what was the potential damage to the amp if that were the case?

2) I've heard that a tube fogging up is not a good sign (tube not sealed or something) but I was wondering about when they "chrome up" what that's an indication of?

New to tubes so I'd like to get some basics down so I know what to be concerned about and what not to be when it occurs.

Also, I buy vintage/used tubes and have no way of checking them out aside from visual inspection before I fire them up, mostly checking all the fillaments are connected, pin condition, just general overall integrity. I've bought about 30 tubes - all pre so far. Most of the guys I've bought from have been pretty reputable and typically have gas/meter read qualifications (which I understand has limitation). But I was wondering if there's anything in particular I need to be looking for?

 

Preamp tubes are cathode, which means pretty much self, biasing, so if one was glowing red it would either be overdisappation or a short. If the cathode were open (no bias) then the tube wouldn't work anyway, so that leaves the possibility of a short causing the plates to glow red.

Since preamp tubes are triodes, you could only have a short from heater to plate (it would blow up the amp so not that) from plate to grid (it would make the tube emit LESS) or from heater to grid (it would knock the bias back enough to drive the tube too hot.)

Since he was talking about the 12AU7 that, IIRC, is the driver tube in that amp. If it were to short itself out, there would be a good possibility it would severely unbalance the output section and cause half the output tubes to go into runaway with oscillations that wouldn't be audible, but would be deadly for the tubes and possibly the output transformer.

FWIW, I think he still has SERIOUS problems but is ignoring them.

If they turn frosted white, they're trash.

The "chrome" is the getter and it's there for good reason, and seing that is a GOOD thing. Leaky or dying tubes start burning that silvery coating away and it turns light brown- THAT's bad.

Get yourself a tube tester if you start messing with power tubes. They're not perfect, but they also won't blow up with a bad tube like an amp can. As long as you stick to preamp tubes, don't worry about it.

 

Guy I bought the THD Univavle from just sent me some parts to the amp he ran across including a Brit Sylvania EL34 tube.

I noticed in handling the tube it "rattles." Like a lightbulb but not as pronounced - pronounced enough to where it was obvious in casual handling. None of the other power tubes I've got do that. I've got one you can stick up to you're ear and tap on it and it's a similar sound but faint at that and definitely nothing that would be heard without doing as much.

Appearance wise, looks fine otherwise. Anyway, thought I'd inquire before firing it up.

 

Sometimes it happens, im sure one of my power tubes rattles, but, there it isnt microphonic (it doesnt come through the amp), so im hoping alls well

 

FWIW:

tube works fine. Appreciate the feedback. I just wanted some input that I didn't have a pat hand for an impending melt-down.

 

how does it sound with the 12AT7s instead of the 12AX7s? is it a lot tamer? and did the 12AU7 make much of a difference? i like the stock sound but sometimes it can be a bit much. im thinking about changing them but i dont know which tubes to buy.

 

FWIW:

don't have a Traynor but in the Uni the pre tubes make a lot more difference than what I expected from what I've read. I expected it to be more like with mic tube preamps. I've bought some 15 different pre used tubes (12a TXUVZ 7 among others) and just in popping them in to check them out they can alter tone as much as some pup changes (and I've done more than my share of those). I've only swapped out a few power tubes but, without actually sitting down and taking a hard look, seems I'm getting more variation between "some" pre tubes than from switching power tubes.

In general it seems like the less gain the softer the tone with less top end. But there are so many variations tube type to tube type, manufacturer to manufacturer, and variables of the same tube within a manufacturer (ie. 12ax7LPS whatever) that it gets real thick in a hurry.

But I can difinitely use a given pre tube to bring out more top end with a given pup or take the harsh top out with another.

 

On the note of trying different tubes, ive got an urge to try a set of KT-90s in my SVT, i dont know what it'll sound like, but it would be interesting im sure

 

You'll have to leave its top off. KT90's are too tall to fit inside an SVT II chassis.

 

That i knew, think you said that before, how would they sound do you think?
Whats the power output of a KT90 compaired to an 88 or 6550?