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Thread: Valve base down.. .

  1. #1
    Join Date: Dec 2012

    Location: Stoke on trent

    Posts: 432
    I'm Steve.

    Default Valve base down.. .

    What happens if a valve base goes down? I've got sound through both channels but noticed the one of my right EL34s wasn't glowing. Swapped the valves around. Same position not glowing. There was a bit of rustling on that side earlier so I re sat all valves. Could I have knocked a connection on the valve seat?? Easy enough to change? Ive git a few days off and was hoping fir a few listening sessions. ..Could I remove one of the left hand valves and use it at half output until i get it looked at or is there a risk of damage?

  2. #2
    Join Date: Oct 2016

    Location: Bolton, England

    Posts: 1,142
    I'm Andrew.

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    Sometimes one of the sockets becomes oxidised or worn and loose. If you're lucky you can fix it just by giving it a good clean and squeezing the contacts a bit so they grip the valve pins properly. Whether they're chassis-mounted or PCB mounted might make a difference but worth trying anyway.

  3. #3
    Join Date: Dec 2012

    Location: Stoke on trent

    Posts: 432
    I'm Steve.

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    I'll give it a go thanks. Typically I have new speakers to listen to.
    If I was to run the amp with one el34 inserted on each side, would there be risk of damage or does the output just half?

  4. #4
    Join Date: Dec 2012

    Location: Stoke on trent

    Posts: 432
    I'm Steve.

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    Amp is a prima Luna Prologue 1 by the way

  5. #5
    Join Date: Oct 2016

    Location: Bolton, England

    Posts: 1,142
    I'm Andrew.

    Default

    Quote Originally Posted by Bourney View Post
    If I was to run the amp with one el34 inserted on each side, would there be risk of damage or does the output just half?
    There's probably little chance of damage but the output won't simply drop by a half. Removing two valves will mean there's less current drain on the heater power supply and less current drain on the HT as well. That means the voltages will probably rise a bit. The output impedance of the amp will also change and generally you shouldn't expect the same performance as with four valves, but it's probably safe to run it with two valaves.
    Disclaimer - do so at your own risk. I didn't say it will definitely be safe.

  6. #6
    Join Date: Dec 2012

    Location: Stoke on trent

    Posts: 432
    I'm Steve.

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    Haha.. I think I'll leave it. Bloody valve amps....

  7. #7
    Join Date: Apr 2012

    Location: Southall, West London

    Posts: 34,564
    I'm Geoff.

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    I wouldn't do it myself.

    This kind of situation is why I always have a spare (back-up) amplifier. A tiny SMSL is ideal.

  8. #8
    Join Date: Dec 2012

    Location: Stoke on trent

    Posts: 432
    I'm Steve.

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    I've got the bottom off. Can't see anything out of sorts.
    The bottom of the pins are quite loose and rattley, is that normal??.

  9. #9
    Join Date: Oct 2016

    Location: Bolton, England

    Posts: 1,142
    I'm Andrew.

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    Quote Originally Posted by Bourney View Post
    The bottom of the pins are quite loose and rattley, is that normal??.
    Yes, it allows them to move a bit when the valve is inserted.
    Sometimes just pulling a valve out and re-inserting it can be enough to clean the contacts.
    I would check the voltage on the contacts for the heater pins if you're brave enough to poke around inside.

  10. #10
    Join Date: Jun 2008

    Location: Happy Cheshire

    Posts: 610
    I'm Duncan.

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    If it's a push pull amp then both tubes are used at the same time in a "push pull" circuit. The channel switching happens before the signal gets to the power tubes.

    Confusion with this type of amp is that power can be cut in half by removing one of the two tubes, this is not how it works. The two tubes are a "team" and taking one out would make half of the output signal and the output transformer search for something to amplify, creating a horrid tone called "crossover distortion."

    Not a practice I would recommend.

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