Power Tube Failure

@jea48 

+1

If you change tubes at recommended times it is very unlikely they will "go out".

Tubes age out typically by hardening sound, or lower output. but occasionally will flash, even less commonly pop.

Very occasionally they will crack and blow... very uncommon, but it does happen. Far more likely with old tubes beyond their recommended usage. 

Under the latter circumstances it may take out the resistor next to the tube... placed there for that very reason to protect the rest of the amp. Seldom it it more than that. 

A friend of mine had a problem with a tube amp from Rogue within the warrantee period and they would not fix it because it was tube related... so I will not buy or recommend Rogue products. 

I have run tubes for a couple decades and never experienced a popped tube. It is uncommon but occasionally happens. 

If you think there may be a couple thousand hours on the tubes... I'd just change them out and reset the counter. Then you can be sure of getting the best sound and know where you stand. 

To all:

Thanks for all of the comments. I seems that I may need to go tube-tester shopping...

@paradisecom - special thanks, I did not realize music/guitar shops may test tubes. 

Also, my question is NOT specific to ARC tubes, but to power tubes in general.  ("I own several power tubes and do not know how many hours of service each has provided".)

Thanks again for relaying you experiences regarding power tubes that have died.

Regards,

In 20 years of tube power amps, I’ve had ONE catastrophic failure: a 1-year old Electro Harmonix KT90, in Rogue Apollo monoblocks (6x KT90 per side) suffered a catastrophic short right at the end of a bass-heavy track played at fairly high SPL:

• Sparkly, moderate level fireworks for a few seconds, followed by a pillar of black smoke. I guess the protective fuses didn’t work in time or were bypassed. 
• Fallout: absolutely toasted a metal-oxide resistor on the affected tube. 1cm of black carbon soot. Singed the PCB trace under the resistor & soot (burned off green mask), but trace was still functional. 
• Still under warranty, so Rogue was nice enough to build a whole new amp board. But the original board would have been functional with a new resistor, tube, and fuses.
• I moved to KT120 / KT88 after this, and have never experienced the issue again.
• This is a worst-case scenario that is very rare in the grand scheme of things.
• I’ve also had Rogue amps pop a tube fuse or 2 (over several years of use), with no other harm done.
• Oops almost forgot I had a bad RFT EL34 tube go cherry-red plating in a vintage Eico HF-87 amp. It was just a bad tube in that case (ebay seller) and the amp main fuse popped quick; no other harm done. The RFT’s sounded really good for the couple seconds I did hear them though!

Over the years I migrated over to (much more expensive) VAC power amps. I’m impressed by their protection circuitry: in the 300iQ amp I had a tube go bad and it instantly got flagged with a red LED, and cut off from power. No bad sounds or other events. No trip back to VAC needed. No fuses popped. Even the pre-iQ 450S has  handled this very well. Just yesterday in fact, seems I received a bad octet of Mullard KT88 from Viva Tubes (shame on them). The tubes were noisy on startup (which is NOT normal) during biasing, though they seemed to settle a bit. Soon as I tried to play music one side started a loud scratchy sound but was quickly cutoff by the VAC with that red LED indicator. Put the old tubes back in and everything was fine. VAC’s protection works quite well and I didn’t even need to replace any fuses. Love it! But I’m going back to paying the premium for Upscale Audio tubes - they burn in 75 hours THEN test & match. I can't recall a single problem with an Upscale-sourced tube. 

tester, nice wood case, says working, 

https://www.ebay.com/itm/178076757705?mkrid=711-53200-19255-0&campid=5338381866&toolid=10001&customid=5e1d02e0-466d-11f1-81b3-663134616639

overhauled and calibrated

https://www.canuckaudiomart.com/details/650316207-eico-666-tube-tester-clean-and-working-fine-calibrated/