One tube in my amp is having a problem, it makes a popping noise through the speakers and the glow in the tube changes at the same time. It does the popping like this mostly in the first couple minutes, but it does smaller, scratchier pops every minute or so after that. I've uploaded a video showing it. Is this a sign of a bad tube, or is it something different to check? I've swapped channels and it followed the tube so I'm guessing that's it but I wanted confirmation before spending the money on a new tube. Thanks!
https://sendvid.com/sc817hnv
https://sendvid.com/sc817hnv
I'm not a fan of the EH 300Bs. I had a brand new one develop a short and it caused a 100V cathode resistor bypass cap to explode its guts all over the inside of the amp.
There are too gas within tube (blue ionization), so it's possible damaging.
BTW I use EH300B for more than a decade, and only one died (filament defected).
BTW I use EH300B for more than a decade, and only one died (filament defected).
I was wondering about the blue glow. Both tubes glow like that, but no other tubes I've used do. If the blue glow normal for 300b?
It's indicating, that inside the bulb freed any gas (mostly from metals), so vacuum not perfect.
If it's not perfect, arcing possible.
If the tube filament heating slowly and anode voltage gets up too much (no load) -over the gas breakdown voltage- possible forming strikeover.
The another occurrence of arcing is within the first smoothing capacitor in PSU.
If it's -more or less- self healing type metal (paper, propylene) capacitor, after the arcing continues to work.
Usually in this case the fuse (in the secondary of power transformer) blowing.
I also have EH3000B, no problem. 2 out of 4 have blue blow when bought as brand new but those blue are on the top. That pop is scary. The pop I encountered was cold solder of coupling cap. Yours sound like bad tube.
The blue colour is iirc from the weak plasma that's generated. It actually means the tube is basically in good condition.
Another arcing possibility is within the rectifier tube if the first capacitor is too large.
Once it lost one 300B after the arcing rectifier tube.
Once it lost one 300B after the arcing rectifier tube.
You can get popping sounds from bad contacts - in the tube socket or elsewhere. Or bad solder joints. Can be a pain to find, though.
Blue on the glass is Pretty. Nothing to worry about.
If you do not like that, then send the tube to me, I will be glad to use it.
If that tube ever dies, the death has nothing to do with the blue glow on the glass (another cause, such as shorts, or outgassing).
I did have some 300B tubes that shorted from filament to grid.
Those tubes have not been manufactured by that company for a decade or two.
Blue between the elements is almost always caused by Gas.
Get a new tube.
(do Not feed the new tube Beer and Chili).
If you do not like that, then send the tube to me, I will be glad to use it.
If that tube ever dies, the death has nothing to do with the blue glow on the glass (another cause, such as shorts, or outgassing).
I did have some 300B tubes that shorted from filament to grid.
Those tubes have not been manufactured by that company for a decade or two.
Blue between the elements is almost always caused by Gas.
Get a new tube.
(do Not feed the new tube Beer and Chili).
The lack of glow after the crack is because the motentary arc inside the 300B has charged cathode bypass cap up so the current through the tube is much lower which takes a while to recover. You may have exceeded the voltage rating of these - I would replace too. Nice video! Other than the breakdown the tube looks normal.