Air Tight 300B Flame Out

@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

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

@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?