Air Tight 300B Flame Out

@gareents In your original post you state the 300B tube was "lit up brightly", if so this is red plating, doesn't have to actually have red plates, this is just the commonly used term. In your latest post you mentioned the blue and green plasma. Depending on what you actually saw this could indicate different issues. If you only saw the plasma and tube wasn't lit up more than normal this indicates loss of vacuum, could mean less likelihood of amp damage,  If the tube was indeed lit up brightly this points to greater likelihood of amp damage. After my issue forgot to mention I opened up amp and thoroughly checked for any discoloration on any component and poked about for any possible cold solders. Only after this did I move to possibility of rectifier tube issue.

My suggestion to you is if you did indeed only have the loss of vacuum issue follow what I did. Check internals for any discoloration, don't worry you won't get shocked if you've unplugged amp for several days, capacitors can hold charge for hours not enough over days to hurt you. Then check solders, if no issues with either of these try a cheap 300B, keep close on power up so can shut down immediately, you get no popping after an hour or two good to go, means WE was issue. If you do get popping, this my experience, try a cheap rectifier tube in place of original, no issue means either bad rectifier tube took out WE, or more likely, WE took out rectifier. And if you still get popping after all this, take to tech.

I'll be interested to hear outcome, you may have had same issue I had with new WE, mine went bad after with about 7 hours on it, 2nd power up. In WE statement on web they claim to have recently installed new equipment for extracting air from tubes. Were they having problems previously? Is the new equipment faulty, my bad rube from October 2024 production date?

Gar,

Based on that detailed description, I think you'll find a smoked resistor.  Possibly another component but resistor is most likely.  

I'll let others comment on the tube glow you saw.  the blue is generally electons escapong the plate and decelerating releasing a blue photo.  but I'm not sure how to correlate this to a failure. 

I like manual bias just because autobias circuits sometimes fail.  Not saying that is what happened but it could be.

Glad to hear there is no question of authenticity.

Jerry

@carlsbad2 ​​​​​@sns  @testpilot 

Thank you for your responses.

The little smoke, but strong smell, was only from beneath the 300B tube that went bad. Probably an indication of fried resistor? No discoloration on the tube socket or on the tube pins.

The tube did not show any sparks, nor a red plate. Rather, inside the tube was a roiling aurora borealis of beautiful blue and green plasma throughout the entire tube. Series of crackles and pops and a final louder pop through the speakers, no noise from the amp itself.

The AirTight ATM-300 uses auto bias.

I purchased the WE tubes from Uncle Kevin at Upscale Audio. Assuming they are authentic.....

@carlsbad2  Thanks for the offer of cheap 300B tubes, but I have some other 300B tubes myself. However, given the smoke and burning smell, I am reluctant to put in another tube. Think I will just bite the bullet and have the amp looked at by a good audio technician. Turns out we have one here in the Sacramento area.

Thanks again to you all.

    -GAR

I hae a cheap pair of 300B electoharmonics.  Let me know if you want me to list them for sale.  Audiogon will kick us both off if we try to do a sale without using the classifieds.

What is the cause of red plating, could be bad tube or loss of bias in amp, don't assume faulty tube. One way to test for this, try a cheapo 300B. But then you likely took out bias resistor or possibly something else in amp.with the smoke issue. I recently experienced a WE failure, in my case loss of vacuum, entire tube encased in opaque blue haze followed by a single pop. Since these were new tubes I was watching very carefully at powering up, was able to immediately shut down amp. No smoke in my case, but burned electrical smell.

In order to determine whether I had damaged anything in amp I next powered up with some cheapo 300B tubes, same pop. Immediately shut down amp and made the call perhaps my Mullard rectifier tube was the issue. Replaced with another NOS Mullard, no issues with my cheapo or Psvane Acme for several weeks now. Have the replacement WE, I'll cross my fingers and try again this weekend. So question is did WE take out rectifier tube or did rectifier tube take out WE? Loss of vacuum far different than red plating, my take is WE took out rectifier.

@gareents I've seen what test pilot said.  But smoke is not normal.  I put a wrong tube in an amp, blew a resistor, replaced it and was making music again the next day (had to order the resistor).  In this instance, the burning smell was more noticable than the smoke.

The good news is when there is smoke, there is usually evidence of what failed--blackened, burnt, or paint discolored--so you can easily figure out where the problem is.  I'd open it up myself and look for the overheated component.

Now the bad news would be if the smoke was from a transformer.  failed tubes can take out the output transformer.  the good news is that replacement trasmformers aren't as expensive as you would think (in most cases.  My amp has hand wound transformers from Bulgaria) and they are not hard to replace. 

Tubes don't often short although they sometimes do.  More often they "red plate" where the current goes up in a runaway positive feedback syndrome.  This usually starts with either too high a bias current setting or a faulty autobias control.  Your initial description didn't sound like simple redplating.  Were there sparkes inside the tube or was the plate simply glowing red?

Finally, I've heard rumors (I don't want to spread rumors, so I am just calling this something to consider) that WE 300B tubes have been counterfeited.  I don't know where you bought yours but consider if they might be fake.  OTOH, I've also heard they have a fairly high infant failure rate which is covered by the warranty. 

All of this discussion is because you mentioned smoke.

Jerry

Some amplifiers use a sacrificial resistor to protect the amplifier when a tube fails.  In most instances, this is a simple fix although stressful when it happens to your $15k+ amp. 

Thanks all.

I have basically the same conclusion. I am thinking that the tube failed (arced), and the smoke was from a fried resistor. 

Rather than put in another tube, thinking that having the amp checked out by a tech is the best corse of action.

@carlsbad2

+1

Yep, occationally a tube goes out. Hopefully it did not take out a protective resistor... but it may have. That is why they are there. 

Red plate, from the sound of it. Is there a failure on your bias board?

Use a cheaper tube to test, incase the amp is the problem. 

Yeah your tube definitely went out that's a bummer luckily WE has a warranty program. And as Jerry says try another tube in that slot to confirm it was the tube not the amp. For Air Tight service try contacting the US importer Axiss:

https://axissaudio.com/contact/

Sounds like a simple tube failure except smoking?   where was the smoke coming from?   did you put a new tube in and confirm the amp is good?  

Jerry