How tubes fail

[hryc111]

I am an incredibly satisfied customer of Moreplay and Crack.  I have never been happier listening through headphones or through my Moreplay>Musical Fidelity solid state>KEF metas setup.

But I'm new to tubes and had a couple naive questions about longevity.

1) I understand that one can expect thousands of hours of tube life in these amps, but I wonder what are the symptoms of a tube going bad?  Do they tend to fail all at once?  Is it subtle or obvious?  Does sound quality degrade long before they technically stop working?

2) Cathode poisoning.  I happen to have gotten a Nixie tube clock for my wife (who loved the physical appearance of my amps), and designers using those tubes worry about cathode poisoning on under-utilized elements in the tubes.  So they deliberately program in random number flashes to prevent  the case where un-lit elements degrade the tube is on but those elements are off.

My question:  Does the same apply to these amps?  Is it especially bad to (accidentally) leave an amp on with no signal going through it?  Or is leaving the amp on with no input signal basically the same as having it on in normal use?  I sometimes forget to turn off my amps....

Thanks in advance for any insights.

[Paul Birkeland]

Tubes can either fail by slow degradation or you can end up with a somewhat sudden failure internally that doesn't give any warning.  The slow degradation is very much audible.

We don't have any unused tube elements in our kits that are also heated, so cathode poisoning isn't a problem.  With your amp powered up and running, DC current is being drawn and the tubes are kept happy. 

[Ascari]

I just experienced a tube failure today.   One on a  Gold Lion 300B no less.   It actually started a few weeks ago when I noticed my left channel had just a hair less output.   Of course I suspected the worst such as cartridge output down the line to speaker connections.   I did get some distinct improvement after reseating all of my cables.   I thought the issue was resolved.   That was until tonight.   All of sudden my left channel's hiss was back with a vengeance.   I rechecked ALL of my connections leaving me with an issue with one of my components.   Since I could simply change from one source to the next, I ruled out the Eros, my tape deck and cd player.    That left something in the Beepre.   I started with the 300B's and switched channels.   To my shock, the hiss followed the tube.   I put in one of the original tubes that I had with the kit and......    Hiss gone!       I do have a tube tester, but it just doesn't do power output tubes.  The bad part about this it I paid about $300.00 for a matched pair.   Now they run from $600.00 to $1,200.00 for a set.   GE is starting to look good.   Anyone with any experience?   
 

[Paul Birkeland]

If you don't have a lot of hours on the 300Bs, I would be reheating the pins to reflow the solder. 

[Ascari]

Nope.   Probably close to 3,000 hours.   Maybe more.   Especially since the noise followed the tube.   The dead silence that followed after installing the original is stark.   

[diynewbie]

If you don't have a lot of hours on the 300Bs, I would be reheating the pins to reflow the solder. 

Reheating the pins on the tube (vs. the socket)?

[Paul Birkeland]

Yes, the pins on the tube itself.  There are little holes in the tip of each pin where the solder is added to connect the pin to the internal wires of the tube itself, and sometimes these aren't 100%. 

[Roamconstant]

Paul,

A 300B tube failed at a suspicious time:

I just finished the BeQuiet Attenuator upgrade.  Right channel had no output after I plugged everything back in.  Made sure it isn't a wiring issue and walked through the entire manual again and couldn't find the error.  I swapped the tubes and the error followed the tube.  I borrowed a 300B from my Kaiju and the problem went away.  The BeePre is playing fine through another amp I have right now. 

The pre-amp worked fine before I took the tubes out a few days ago to complete the upgrade.  Perhaps a connection within the tube severed as I removed it from the socket on the amp?  Or super bad timing?  Something I'm not thinking of?  The tube glowed and appears the same as others when amp is powered. 

Heating up the pins didn't fix them as you recommended yesterday.  Time to buy new tubes and move on with life, or should I be critical of the work I just did on the BeePre?

Thanks,
Frank

[Paul Birkeland]

Yes, having a failure like that would definitely have me at least trying to reheat the solder in the pins, as an internal wire may have popped loose from the tube being moved around.