Winged "C" goes thermonuclear

[x3workshop]

I have a very dear friend and colleague who has a deep appreciation for tube amplification - the sound they are capable of reproducing, as well as the design aesthetic.

As gratitude for her work on various projects we've done together, I have given her a pair of rebuilt Heathkit UA-1 monos as well as a Cayin TA-30 integrated that had Paul Gryzbeck of Tube Audio Design's full upgrades.

I got an email from her this morning with the subject title of: "Do I need the fire extinguisher?" with the following photo attached.


It was tongue in cheek as she had shut it down as soon as she saw it. Well, after she took a picture of it...

She said she had turned it on and went about her morning and noticed it about 15 minutes later. I suspect it had been that way for at least 10 minutes. I'm pretty sure this may have been fatal for some of the components. Especially the OPT. We'll see when I get my hands on it.

Pity if it's toast.

 

[kve777]

Ouch!

 

[x3workshop]

Exactly

 

[AdamAnt316]

Yeah, that's fatal to the tube, at the very least. Hopefully, it didn't take anything with it, and its pair-mate appears to be acting as if nothing's wrong, so the bad tube probably just spontaneously developed a short or whatnot. A shame to lose a tube like that, but that's just how it goes sometimes, methinks.

When I had issues with my ST-70 red-plating, it was within 5 or so minutes of me powering the amp up, and only part of the plate started glowing red. I caught it within 30 seconds of the fault, and shut it down immediately. Swapping the output tubes made the issue go away, with no audible damage to the 'bad' tube as far as I can tell, and the issue has yet to recur ***KNOCK ON WOOD***.

I'm rather amazed that she left it on long enought to take the picture; as soon as I realized what was going on with my ST-70 (like her, I had no signal going through it, just started hearing 'tinkling' noises from the amp), I immediately leapt for the shut-off button. Granted, I doubt it would'ved saved the tube, but it would've prevented any further damage to the amp, if any occurred. In any case at all, yet another reason to not leave this stuff turned on when unattended, especially if there's no signal going through it.
-Adam

 

[whoaru99]

Don't think I've seen a red plate worse than that on single tube.

 

[hugo454]

my Jolida 302 redplated last week.I shut it right down,however it would not turn back on.I thought the worst, took out my meter only to discover the only damage was to the on/off switch.An $11 dollar replacement from digikey and back in biz.replaced all 4 tubes with another set I had also.Hopefully that one will not be as toasted as you may think.fingers crossed.

 

[x3workshop]

I think it's a bit exaggerated in that photo. I'll get it on the bench this week and check it out.

 

[trainbuftony]

If it was red plating like this then the transformer was definitely conducting. The tube or tube socket failed or perhaps a coupling cap? It happens, and usually with tubes everything ends up being ok in the end. Is there a cathode resistor in this amp? Checking it for drift might be prudent after this unfortunate event.

 

[sKiZo]

I'll see your red plate and raise you one ... <G>

(and yah ... that may be a tad bit exaggerated ... )

 

[AdamAnt316]

I'll see your red plate and raise you one ... <G>

(and yah ... that may be a tad bit exaggerated ... )

Dr. Strangetube or: How I Learned to Stop Worrying and Love the Glow

(hears a distorted rendition of "We'll Meet Again" playing at low volume)

 

[x3workshop]

I'll see your red plate and raise you one ... <G>

(and yah ... that may be a tad bit exaggerated ... )

I knew you'd go there.

 

[x3workshop]

If it was red plating like this then the transformer was definitely conducting. The tube or tube socket failed or perhaps a coupling cap? It happens, and usually with tubes everything ends up being ok in the end. Is there a cathode resistor in this amp? Checking it for drift might be prudent after this unfortunate event.

Yeah, I'll be checking things thoroughly.

 

[Dneprrider]

Now for some appropriate music

 

[PakProtector]

I'll see your red plate and raise you one ... <G>

(and yah ... that may be a tad bit exaggerated ... )

If that is a single GZ34 under the mushroom cloud, not all that exaggerated...

Also, I had seen a few pics of tantalum anode, transmitting tube amps running. I then built one myself, and saw nothing like what I had seen in pics. I did get a pic taken of the amp, and the camera can add a few degrees to the glow.
cheers,
Douglas

 

[sKiZo]

Yah ... GZ34. Those tend to be kinda borderline on the Latino amps. Tried the coppercap and didn't much like it and eventually went with a tasty little GZ37. That's been doing the job for several years now and I scored a couple of spares before the prices got ridiculous.

 

[jharris]

I did get a pic taken of the amp, and the camera can add a few degrees to the glow.
cheers,
Douglas

Many cameras will interpret infrared as red, or even white light, especially older (or cheap) digital cameras.

 

[derekva]

Low light can make a bad situation WRT red-plating look worse. I've done long exposures of tube gear in very low-light conditions that look like an impending meltdown, yet under normal lighting, there is no trace of a glowing plate.

For example:

I think in this case, the glow of the heaters on the 6EU7 driver / phase inverter tubes is being reflected off of the plates in such a way that the two outside EL84s look like they are about to melt down.

(but in the OP photo, that Winged "C" is definitely winging its way to the afterlife)

-D

 

[AdamAnt316]

Red-plating isn't always bad. Some tubes in some applications red-plate by default, and can do so for a very long time. Here's a pair of 3-500Z transmitting tubes glowing away happily in a ham radio linear amplifier:

Granted, they won't last as long as an EL34 babied in an audio amplifier, but they're not on the verge of melting down, either. They likely have attributes most audio tubes don't have, like graphite plates. Even audio-type tubes can be coaxed to go well outside of their comfort zone in certain circumstances; some ham radio operators built transmitters which managed to coax 100 watts (in class C) from a metal 6L6 sitting upside-down in a bucket of oil. They likely didn't last very long in said application, of course, but they didn't turn to slag, either.
-Adam

 

[DC]

Red-plating isn't always bad. Some tubes in some applications red-plate by default, and can do so for a very long time. Here's a pair of 3-500Z transmitting tubes glowing away happily in a ham radio linear amplifier:

Granted, they won't last as long as an EL34 babied in an audio amplifier, but they're not on the verge of melting down, either. They likely have attributes most audio tubes don't have, like graphite plates. Even audio-type tubes can be coaxed to go well outside of their comfort zone in certain circumstances; some ham radio operators built transmitters which managed to coax 100 watts (in class C) from a metal 6L6 sitting upside-down in a bucket of oil. They likely didn't last very long in said application, of course, but they didn't turn to slag, either.
-Adam

The Amperex 3-500Z plates in my AL80 amp get all glowy. I try not to look at it...

 

[x3workshop]

Got the amp this morning. Visual inspection shows nada underneath. No roasted resistors or crispy caps visible. I'll measure everything, but it seems that the housekeeper may have dusted a bit too vigorously and knocked that tube askew. Enough to lose bias contact. We shall see.