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Thread: Tube rectifier wear

  1. #1
    Member Roberto Lasco's Avatar
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    Tube rectifier wear

    I always thought tube rectifiers are "on-off" devices: that they performed evenly until the day they die. It seems it's not the case.

    I was working on a SF Princeton amp with a B+ abnormally low - 380V. Idle current was fine etc. I swapped the 5U4 and bingo, 430V !
    The old rectifier tested VERY bad indeed on my Stark.

    This thing was about to die or it could perform that way for years to come ?

    thoughts ?
    roberto

  2. #2
    Senior Member Old Tele man's Avatar
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    ...typically, the "problem" with rectifiers is cathode emission decline...due to posioning or simple wear-out due to age.

    ...do an emissions test between the old and new tubes for a comparison.
    ...and the Devil said: "...yes, but it's a DRY heat!"

  3. #3
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    It is more common for a rectifier to stay closer to its original voltage till death,but they are tubes and do wear out,as you see in your example,but I dont recall ever seeing one drop that much voltage.My guess is that tube would have shorted out and died very soon from over current.

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    Senior Member Enzo's Avatar
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    There is no "this is how they fail" list for rectifier tubes or most anything else. Maybe some failure modes are more common than others, but about the time you think you have seen it all, you see something new. I have been soldering for about 55 years now, and I learn something new every day.

    You could have a tube that was about to fail completely, or it could indeed have worked that way for a long time. Who knows? If we were to determine why the voltage drop was so high, we might be able to predict better. Yo0u coulod have worn out cathodes, you could have one side not working, and so on.
    Education is what you're left with after you have forgotten what you have learned.

  5. #5
    Member Roberto Lasco's Avatar
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    Yep, did the emission test, kinda like 20% of the VU for the old tube against 80% for the new one (there's no specific scale for rect tube testing).
    I always thought that cathode poisoning was due to keep filament hot without high voltage applied. Don't understand how this can be pertinent to rect tubes...

    Tube show no shorts at all, and both diodes were working; in fact amp sounded pretty good except for some underpowered feel.

    I was wondering if I could use that tube for some "zenering" purpose, but probably would be unreliable anyway, so I trashed it.
    I guess I can't take (anymore) for granted that all tube rect that are working are ok...

  6. #6
    Lifetime Member Rob Mercure's Avatar
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    The issue isn't cathode poisoning - which is a replacement of the top cathode layer with a non-emissive coating - but instead simple loss of material as the cathode material boils off with time.

    Rob

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    hey Rob, good to see you posting. Hope all is well.

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    Lifetime Member Rob Mercure's Avatar
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    Hey Dai,

    Thanks for asking. Am still struggling - in addition to the weird tropical liver virus I've also been found to have an underactive thryoid and a heart arhythmia - unfortunately treating the thyroid stuff has delayed the chemo to knock out the virus. But the good side is revving up my thyroid has given me much more energy and clarity of thought and so I'm finally catching up on a backlog of repairs. Acoustic guitar work for the present before I hit the electronics again.
    Ironically the heart doc has suggested that if I were put on blood thinners for a while, sedated, and my heart selectively shocked that the normal rhythm can be restored - as many times as I've shocked myself over the past 40 years or so with a distinct variety of currents. voltages, phases, and frequencies you'd have thought that I would have hit the right combination on my ow

    Anyhoo I'm going to try and contribute more to the board as my energy increases but try to limit myself to areas that other's aren't covering as completely (not that any subject has ever lacked for complete coverage on this - and the preceding - forum). I've been spending some time on the frets.net board which is primarily guitar repairmen and builders and since there's a notable lack of an electronically trained - music world seasoned - "expert" I've been "a-tryin to learn 'em folks." (what's an "ex-pert?" Well an "ex" is something used up and a "pert" (pronounced "spurt.") is a drip under pressure <grin> - from my old community organizing days).

    How are you doing?

    Rob

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    Senior Member Enzo's Avatar
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    Geez Rob, take care of yourself.

    Remember: it ain't healthy to be sick.
    Education is what you're left with after you have forgotten what you have learned.

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    hey Rob,

    not much going on. I keep getting tendonitis flare ups which is kind of annoying(ibuprofen = relief) since diy stuff really involves hands a lot (as I'm sure needs not being pointed out). Okay today though.

  11. #11
    Supporting Member tubeswell's Avatar
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    Hi dai h.

    FWIW I found that my tendonitis and arthritis, a bit of bee venom cream rubbed into the joints helps take away the pain. Works wonders like magic (You have to get the bee venom ointment from health shops (or some apiarists also produce the stuff)
    Building a better world (one tube amp at a time)

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    Talking

    Quote Originally Posted by tubeswell View Post
    (You have to get the bee venom ointment from health shops (or some apiarists also produce the stuff)
    ... darn it, I was just about to don my beekeeper's outfit so I could find a bee hive to stick my hand into

    thanks for the tip!

  13. #13
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    Quote Originally Posted by dai h. View Post
    ... darn it, I was just about to don my beekeeper's outfit so I could find a bee hive to stick my hand into

    thanks for the tip!
    I used to know an old boy who swore by that. He kept bees just for the exposure, Here's the story he told.

    He'd been working for Boeing and his arthritis got so bad he moved back to Michigan and there he was, 45 years old, living in the same bedroom he'd grown up in.
    So he was doing pickup work, cleaning up trash, and a neighbor asked him to clean out some bees that were nesting in an old barn back on the farm. He said he'd gotten stung pretty good and the next day he felt better than he had in years.

    So he went and got the stuff to set up a few hives here and there and hadn't been troubled since.

    Come to think of it I could probably use some of that myself because being 61 is not nearly as much fun as I thought it was going to be.

  14. #14
    Supporting Member tubeswell's Avatar
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    Yeah well laugh to your heart's content - I have found it works for me as long as I use a little bit at a time. Whatever it has got in it, it kills the pain from RSI or arthritis. (But if you slap too much on at once you get an allergic reaction - so don't bother if you are allergic anyway). I knew I could find something about it in the venerable wiki (not that I'm aiming to undermine the credibility of the stuff).

    Apitherapy - Wikipedia, the free encyclopedia
    Building a better world (one tube amp at a time)

  15. #15
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    sorry tubeswell I didn't mean to imply that it wasn't true! Just trying to be a comedian (and failing, lol). Bee venom may not be covered by the national health insurance thing though.

  16. #16
    Supporting Member tubeswell's Avatar
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    Don't worry dai, I got thick skin (from all that bee venom ointment ).
    Building a better world (one tube amp at a time)

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