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Classic 30 gone weird!

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leerockerleerocker Frets: 607
in Amps
Picked up a c30 head a while ago and it had this intermittent problem where the power tubes weren't coming on and turning it off and on seemed to remedy it. Turned it on last night and was making some weird crackling noises and a considerable volume drop and everything distorted.  Turned off and on again and still doing it I noticed one power tube was almost looking like it was going to blow up so changed all the el84s and it's still doing it. Any ideas amp experts?
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Comments

  • ICBMICBM Frets: 72605
    The valve filaments are in series on these, so a bad contact or a faulty filament anywhere in the chain will stop all four working. One power valve running way too hot (and it not being the valve) sounds like a bias supply failure to that socket, which could either be a socket contact problem or a dead grid stopper resistor. These things might be related if a previous valve failed, although I can't quite think how!

    If changing the valves hasn't helped, it's a trip to a tech I think - these amps are a complete pig to work on.

    "Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski

    "Only two things are infinite - the universe, and human stupidity. And I'm not sure about the universe." - Albert Einstein

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  • leerockerleerocker Frets: 607
    Thanks icbm I had a quick look and that pcb is a stupid design! Shame they are a pita to fix as I quite like em. Cheers for your wisdom as per usual I'll get it over to rift to have a look 
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  • RiftAmpsRiftAmps Frets: 3180
    tFB Trader
    Just to follow up on this...

    Amplifier presented with the above symptoms, a visual check revealed cracked solder joints on all four EL84 bases, both reservoir caps (C39+C40) leaking electrolytic, and a shorted diode (CR4 - SR2873).

    Swop out, reflow, and put back together along with the ICBM R67 mod.

    Test valves - All good.

    6-hour soak test at rated OP power. Done.
    *I no longer offer replacement speaker baffles*
    Rift Amplification
    Handwired Guitar Amplifiers
    Brackley, Northamptonshire
    www.riftamps.co.uk

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  • ICBMICBM Frets: 72605
    RiftAmps said:

    the ICBM R67 mod.
    Fame at last!

    :)

    "Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski

    "Only two things are infinite - the universe, and human stupidity. And I'm not sure about the universe." - Albert Einstein

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  • martmart Frets: 5205
    ICBM said:
    RiftAmps said:

    the ICBM R67 mod.
    Fame at last!

    :)
    Did you pick R67 to change just because that was your birth year?
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  • crunchmancrunchman Frets: 11470
    To the OP, now it's working, sell it while the going is good, and get a Hot Rod Deluxe.
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  • p90foolp90fool Frets: 31659
    mart said:
    ICBM said:
    RiftAmps said:

    the ICBM R67 mod.
    Fame at last!

    :)
    Did you pick R67 to change just because that was your birth year?
    I think we should ALL do that to our amps then report back here. 
    :)
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  • springheadspringhead Frets: 1602

    I've got a JTM45, a Tweed Deluxe and a Pro Junior.  None of those have my "birth year resistor" R66, and I really wanted to join in!


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