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Thread: valve problem

  1. #11
    Join Date: Apr 2012

    Location: London

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    I'm James.

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    Hate to be a downer but if you saw flashing then 100% it isn't dirty contacts and it needs attention. This is more likely arcing in one of the power tubes and quite likely caused as you surmised by switching off and then on too quickly. If the valves survived then they may be compromised and need proper checking (a simple valve tester may not show up the effect, you'll need a curve tracer). Or you could buy new and wait till the opportunity presents to find which have survived. I don't know the amp or the protection it has but better safe than sorry.

    Sent from my BLA-L09 using Tapatalk

  2. #12
    Join Date: Aug 2012

    Location: Eton wick

    Posts: 1,677
    I'm Philip.

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    Quote Originally Posted by Jazid View Post
    Hate to be a downer but if you saw flashing then 100% it isn't dirty contacts and it needs attention. This is more likely arcing in one of the power tubes and quite likely caused as you surmised by switching off and then on too quickly. If the valves survived then they may be compromised and need proper checking (a simple valve tester may not show up the effect, you'll need a curve tracer). Or you could buy new and wait till the opportunity presents to find which have survived. I don't know the amp or the protection it has but better safe than sorry.

    Sent from my BLA-L09 using Tapatalk
    According to tne amp spec-
    Tube plate fuse Protects the amplifier output stage. Other amps may need a trip to the shop if a tube fails. Not this one. Just plug in a new tube and fuse, and go.

    I do seem to have a habit of ballsing up.
    The last time i put winged c svetlana el34 into an amp, audio innovations 700, i inserted one with the guide pin out of line (very worn sockets) and had to get it repaired.
    John wood charged me 80 quid to fix and put in a set of good used 5881.

    I have form!

  3. #13
    Join Date: Aug 2012

    Location: Eton wick

    Posts: 1,677
    I'm Philip.

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    Should the plate fuse be adequate protection until i find someone to check them over?

  4. #14
    Join Date: Aug 2012

    Location: Eton wick

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    I'm Philip.

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    Is there anyone on these forums that has tne ability to test tubes thoroughly?
    Or any reccomendations?

  5. #15
    Join Date: Apr 2012

    Location: London

    Posts: 685
    I'm James.

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    There are people around with curve tracers which is what you need rather than a single operating point type of measurement like most valve testers produce. Henry (toprepairman on the old 'Wam) has one and I'd be surprised if Graeme at Amp Regen can't test them thoroughly as well.

    Is the amp safe with the old power valves? Maybe, Primaluna claim not to run the valves hard, but the arcing is likely caused by too high anode voltage. I suspect it is also likely to have affected one power valve rather than all of them. So the valve might still behave OK, or could be flaky and dangerous, or it could work fine but just with a bit of added distortion/non-linearity. That's what the tests are for.

    To my mind it seems unwise to leave the amp exposed to possible damage for the cost of a bunch of relatively cheap cooking tubes to tide you over whilst you get the valves checked...

    Sent from my BLA-L09 using Tapatalk

  6. #16
    Join Date: Dec 2008

    Location: East Riding of Yorkshire these days

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    I'm Shaun.

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    Not too sure about the amp in question but my Prima Luna has an LED in front of each power tube that indicates a fault with its associated valve. Even with this in mind though I had a problem when I borrowed a set of KT88's and tried them. Every time I switched the amp off there would be a cracking sound out of each speaker. Not so with the bog standard EL34's.

  7. #17
    Join Date: Oct 2016

    Location: London

    Posts: 313
    I'm David.

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    Quote Originally Posted by Jazid View Post
    There are people around with curve tracers which is what you need rather than a single operating point type of measurement like most valve testers produce. Henry (toprepairman on the old 'Wam) has one and I'd be surprised if Graeme at Amp Regen can't test them thoroughly as well.

    Is the amp safe with the old power valves? Maybe, Primaluna claim not to run the valves hard, but the arcing is likely caused by too high anode voltage. I suspect it is also likely to have affected one power valve rather than all of them. So the valve might still behave OK, or could be flaky and dangerous, or it could work fine but just with a bit of added distortion/non-linearity. That's what the tests are for.

    To my mind it seems unwise to leave the amp exposed to possible damage for the cost of a bunch of relatively cheap cooking tubes to tide you over whilst you get the valves checked...

    Sent from my BLA-L09 using Tapatalk
    IME valves that flash over like this will often continue working and will also test fine on a curve tracer, before eventually failing prematurely (or not). If I'm at all dubious of an amp's protection I replace. The best protection systems are electronic but few manufacturers even of expensive amps fit them because of cost and also the fact that fuses will protect in quite a high percentage of cases. Bare in mind many fuses used in even expensive amps are rated at 250v ac and are used at much higher DC voltages. Used at higher voltages the fuse can 'blow' leaving enough molten metal plating the glass cylinder to still allow conduction. My Mastersound Monoblocks use such 250v rated fuses to 'protect' the 1.2kv HT but are probably as much use as a chocolate teacup. Fuses also affect sound quality when placed in HT lines. A better place to put them is in the HT ac feed, where they won't affect sound quality, and where the volts will be AC and nearer the fuses rating, but need to be specced for the switch on capacitor charge surge. Which brings us back to properly implemented electronic protection as the best system.But having given those scare stories I've never had an output valve blow a transformer when failing as Ive generally been in the room and get to that off button pretty quickly!

  8. #18
    Join Date: Aug 2012

    Location: Eton wick

    Posts: 1,677
    I'm Philip.

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    I did contact several companies/people about this.
    I was told by one very knowledgable chap that it was impossible to tell if they werr compromisef. He told me to visually inspect for debris, pitting, colourations, etc. If all apieared fine and after a few hours all was well, then chancs are i'd gotten away with it.

    Primaluna told me not to worry as there is a plate fuse. They make a big deal of this in their sales blur.
    They said keep an eye out for 20 to 30 hours and replace if it flashes again.
    If valve goes thrn simply replace fuse.

    So far all ok after a coiple of half hour listens.

    Can anyone be sure thr nos or used valves they have bought have never flashed in similar circustances? Probably not.

    I will kerp an eye out or an ear out for the tell tale flutter noise, but not going to worry about it top much.

    I will of course wear rubber wellies at all times.

  9. #19
    Join Date: Oct 2016

    Location: London

    Posts: 313
    I'm David.

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  10. #20
    Join Date: Oct 2011

    Location: Glasgow

    Posts: 1,049
    I'm Paul.

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    Quote Originally Posted by simon g View Post
    What you’ve done is a no no in the world of valves. Never turn a valve amp off and then on again in quick succession. Always let the tubes cool down before switching on again; about 10-15 mins is usually OK. I would also avoid running it without the speakers connected.
    Is this also the case for valve phono stages?

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