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Why so many tube changes

Discussion in 'Amp Input - Normal or Bright' started by Birdsong, Sep 12, 2018.

  1. Namelyguitar

    Namelyguitar Most Honored Senior Member Strat-Talk Supporter

    Jun 3, 2009
    Mobile Bay
    There's lots of non-expert advice perpetuated on the web. I hope that some of the healthy 'old' tubes that people replace might be put to further use, later.
     
    abnormaltoy and Birdsong like this.
  2. Robins

    Robins Dr. von Loudster Strat-Talk Supporter

    Dec 22, 2010
    Germany
    My ENGL Blackmore still has the original tubes from 1995 in there. Sturdy russian unbreakable 5881s.
    My JCM800 still has the Siemens (power)tubes in there I bought when I got the amp back in the ´80s.
    Yes, quality tubes can stand decades when you are not pushing them really hard every night on stage.
    I have to add both amps don´t really push the tubes real hard anyway.
    High voltage? yes, but that is never a real problem for (power)tubes.

    All the best,
    Robin
     
  3. rocknrollrich

    rocknrollrich Senior Stratmaster

    Age:
    47
    Jan 8, 2016
    philadelphia
    I have had an output transformer die from a tube failure. A jcm 800.

    I had the amp cranked when it happened. The amp went from very loud, to very weak, to near silence in about 10 seconds.
    Burnt output tube.
    I put in another quad of tubes and no change.
    Yanked the xformer and did some tests on it. 1 half of it was almost completely shorted.
    I actually posted about it on the music electronics forum. I don't know if I'd be able to find the post, as this was years ago. If i can find it, I'll post a link.

    Anyway, i also have been playing thru tube amps for more years than I'd care to mention. Now, this has only happened to me once. And i have had a lot of different amps come and go over the years.
    So i don't want to be an alarmist and advise people to change good tubes for no good reason.
    However, they have a finite amount of hours in them. I wouldn't wait for them to melt before i changed them.
    It just doesn't make good sense.

    As they age (with use), they lose their punch, their volume, and bass response. And eventually , they die.

    So why would a player who values their tone want to play on worn out tubes, and wait for them to die?

    It's just my opinion. I'm not a tube salesman, and i generally don't care what others do with their gear.

    Oh, incidentally, my Marshall didn't blow a fuse when rgis happened.
    I'll look for the link to my post about it if you're interested.
     
    carver and abnormaltoy like this.
  4. Triple Jim

    Triple Jim Senior Stratmaster

    Feb 27, 2018
    North Central NC
    I'm not saying you're wrong, but could the transformer have shorted and caused the tube to fail instead? It would be pretty hard to tell after they're both bad.
     
    rocknrollrich likes this.
  5. rocknrollrich

    rocknrollrich Senior Stratmaster

    Age:
    47
    Jan 8, 2016
    philadelphia
    Well, that certainly could be the case, and I'd have no way of knowing for sure....... but i think the tube taking out the xformer is the more likely scenario.
    Would you agree?
    Tube failure is more common than output xformer failure, in my experience anyway.
     
    Triple Jim likes this.
  6. Stormy Monday

    Stormy Monday Most Honored Senior Member Strat-Talk Supporter

    Jan 19, 2011
    somewhere
    On my first tube amp, VHT Special 6 Ultra, it showed up with a rattling 12AX7. My second tube amp, a VHT 12/20, I started playing with tubes to quiet some noise (generic Chinese 12 AX7) and play with various output tubes to hear differences. I had a 1979 Pro Reverb for a few years that just ran. A couple of months ago the tube (JJ 12AX7) for the reverb on my DRRi started going bad. So I'm ok with this. Doesn't seem excessive. And I am anything but an expert,
     
  7. Triple Jim

    Triple Jim Senior Stratmaster

    Feb 27, 2018
    North Central NC
    I don't know. When it comes to one failing and wrecking the other one, I'm lucky to have no experience. The one thing that makes me think the transformer could have failed first is how fast it all happened. I would have guessed that if the tube shorted it would have taken a little longer to overheat the transformer enough to kill it. But that's only speculation.
     
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  8. roadhog96

    roadhog96 Strat-Talker

    Age:
    67
    306
    Oct 11, 2017
    CT
  9. RJ Squirrel

    RJ Squirrel Strat-Talker

    Age:
    64
    435
    Jan 28, 2018
    Frostbite Falls
    My guess as to the transformer failure would be flyback voltage spikes penetrating the insulation of the OT primary windings. Marshall and other manufacturers added flyback protection diodes between the primaries and ground in later model amps.
     
  10. rocknrollrich

    rocknrollrich Senior Stratmaster

    Age:
    47
    Jan 8, 2016
    philadelphia
    I was thinking the same thing, or if i remember correctly, that is what was suggested to me on the music electronics forum.
    I'm not a tube amp guru or anything, so i was kinda assuming the tube took out the xformer.

    The other reason i was thinking that way is, i have had many really old amps, and i have only had the one experience with a failed ot.

    I've had plenty of tubes die over the years. Only one ot.
     
  11. carver

    carver The East Coast Strangler Strat-Talk Supporter

    ah

    good point about the OT

    that would make way more sense.

    there is a fuse between the power tubes and everything else. if a tube goes bad, the safety net will step in. if an OT goes bad, then everything goes bad.

    @Robins

    correct me if Im wrong.. and no offence to Rich at all..
     
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  12. RJ Squirrel

    RJ Squirrel Strat-Talker

    Age:
    64
    435
    Jan 28, 2018
    Frostbite Falls
    There's no way of knowing the actual cause for failure. It could have been the tube, but more likely flyback voltage IMO. Regardless, changing output tubes as part of periodic preventative maintenance is not a bad idea IMO, especially with new production tubes. RJ Squirrel SWAG puts expected life for current production tubes somewhere between 500 hours and 1,000 hours.:)
     
  13. roadhog96

    roadhog96 Strat-Talker

    Age:
    67
    306
    Oct 11, 2017
    CT
    I’ve read this a few times over the years that MOST new old stock tubes had lives estimated in the 10,000+ hour range. I doubt I will ever find out if this is true or not but it is a fact that the vintage tubes were very robust especially the ones manufatured for the military, JAN.
     
  14. Triple Jim

    Triple Jim Senior Stratmaster

    Feb 27, 2018
    North Central NC
    10,000 hours sounds reasonable. An old TV that was on 12 hours/day took a little over two years to get to 10,000 hours. I would expect a new set of tubes to last that long. 12 might sound high, but I still know families still leave TVs on nonstop during waking hours.

    I'll be pretty surprised if newly manufactured tubes are shot after just 1,000 hours. Maybe I'll end up being surprised though. I have a new 6V6 in my '57 Princeton clone, and that gets used enough that I'll be to 1,000 in a year or two.
     
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  15. RJ Squirrel

    RJ Squirrel Strat-Talker

    Age:
    64
    435
    Jan 28, 2018
    Frostbite Falls
    Some, but not all, of the old production Mullard and RCA tubes were rated for 10,000 hours of use. If I'm not mistaken most tubes were rated for 3,000 to 5,000 hours. Mullard had an EL84 that they rated for 10,000 hours. The RCA Command series and GE 5 Star tubes also come to mind. But even in the 60s and 70s tube failure was not rare. That's why you could buy them at the drug store. My 500 to 1,000 hour estimate may be a bit conservative, but for someone that gigs with their amps, better to be safe than sorry IMO.
     
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  16. JustABluesGuy

    JustABluesGuy Senior Stratmaster

    Sep 3, 2016
    Houston, TX
    Report back on that!
     
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  17. Triple Jim

    Triple Jim Senior Stratmaster

    Feb 27, 2018
    North Central NC
    I certainly remember the days when People's Drugstore up the street had a row of three big tube testers, and racks of tubes. It's pretty amazing to think of a time when buying tubes was like buying groceries, and two testers weren't enough to keep the lines short. I guess if you figure that a TV had at least 16 tubes in it besides the picture tube, once the set got old enough for tubes to start needing replacement, you had to make occasional trips to buy more.

    I wonder how many good 6V6 tubes got thrown away as the old sets were retired. They were often used as the audio output tube. Here's one that has a 6L6 for the horizontal sweep tube.

    http://www.earlytelevision.org/pdf/rca_trk90_120_schematic.pdf
     
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  18. Robins

    Robins Dr. von Loudster Strat-Talk Supporter

    Dec 22, 2010
    Germany
    There are scenarios the fuse does not blow. Rare, for sure but they happen.
    If that was the question.
    About the Marshall - sometimes those Marshall amps suffered caused by a bad speaker jacket (CLIFF !) and therefore many people thought it must be a bad OT which was not the culprit.
    Many OTs from Marshall burned (partly shorted) because of cranking the amp and the amp got unstable (high frequenzy oscillation). Plexi amps at most.

    All the best,
    Robin
     
    carver likes this.
  19. carver

    carver The East Coast Strangler Strat-Talk Supporter

    thanks man
     
    Robins likes this.