Amp that has been in storage for years ...

Discussion in 'Let's Talk Vintage' started by Mick10, Jan 19, 2020.

  1. Mick10

    Mick10 Member

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    I really enjoy this forum and how the experts share their rare knowledge of these vintage amps. I see that some have posted that for amps that have sat un-powered for years, it can damage them if you power them up, and that it is advisable to have a competent tech do it. Many of these high powered amps are too loud so they sit unused. How long is "too long" for a vintage tube amp to sit unused, as far as damage is concerned? Does an amp need to be plugged into a speaker cab when it is powered up even if you're not going to play an instrument through it? How often should a tube amp be powered up to keep it healthy?

    As a side issue, for amps that are "too loud" for home use, is one possible solution (instead of a MV) to plug it into a Variac and just dial down the voltage so you can push the amp without going deaf?
     
  2. ricksdisconnected

    ricksdisconnected Well-Known Member

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  3. mickeydg5

    mickeydg5 Well-Known Member VIP Member

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  4. South Park

    South Park Well-Known Member

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    The filter caps need to be reset if sits unpowered to long really old stuff. You pull all tubes and slowly power up with a vareac over several hours. I don’t think most tube amps are that old enough to do this .
     
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  5. Mick10

    Mick10 Member

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    thank you South Park
    the reason I ask is because of this thread
    http://www.marshallforum.com/threads/how-much-for-a-1971-superbass-in-immaculate-condition.98996/

    Matthews guitars wrote: "... It's a sure bet that it hasn't been powered up in many years so it should be powered up only by a technician who knows how to reform capacitors, or replace them, before hitting the power switch. Otherwise they could fail very spectacularly. The worst thing you can do to electrolytic capacitors is leave them sitting with no voltage applied to them for a long time, and this could easily have not been powered up in thirty years or more".
     
  6. Dogs of Doom

    Dogs of Doom Moderator Staff Member

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    some cap's have been sittng since the '40s & someone fires the amp up & no issue. Others, have been sitting since 2005 & a few days after firing it up the 1st time, a cap goes.

    In other words, all cap's are different & while 1 cap can be stock from 1966, & the amp sat & have no problems, another identical cap, in the same amp could fizz or blow at any time.

    If 1 cap goes, then others could go as well, so, at that point, if you take it to a tech, might as well have him do a cap job...
     
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  7. MickeyJ

    MickeyJ Well-Known Member

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    What I do is pull the 500ma or 1 amp output transformer fuse, make sure the main fuse is correctly rated and then just fire it up ( after checking the filter caps arent actually leaking or swollen) They either blow or they don't ( at the main fuse). They rarely do. very rarely.
    Then I'll let it sit there for a time, maybe an hour or two.
    Then I put fuse back in and play the bitch.
     
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  8. MickeyJ

    MickeyJ Well-Known Member

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    If the amp has paper style filter caps, nothing gets turned on, they get ripped out and new ones put in and then the amp gets turned on.
     
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  9. MickeyJ

    MickeyJ Well-Known Member

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    If the amp is from the 1940's ( I've repaired amps from the 1930's) there will probably be other issues, dry solder joints, dust and crap and cockroaches you have to clean up. Almost always the tubes are weak, there may be leaking signal caps. I install discreet fuses into these things or advise people to let me, as all the ones I've seen don't have any fuses anywhere.
     
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  10. Mick10

    Mick10 Member

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    are there '60's Marshalls that are untouched (except for tubes) and still playable? I see conflicting reports about that
     
  11. Ned B

    Ned B Active Member

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    I have plenty. Though tubes, filter caps & resisters that have drifted need to be replaced. Fortunately NOS components are available. When you own vintage Marshalls you need to keep Piher, Iskra resistors & Philips caps on hand not to mention NOS tubes make a big difference.
     
  12. mickeydg5

    mickeydg5 Well-Known Member VIP Member

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    Eh.
     
    Last edited: Jan 20, 2020
  13. neikeel

    neikeel Well-Known Member

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    Normally I would inspect the amp for burned and clearly damaged parts and do static tests on all the resistors, check the filter caps for bulging and for leaking electrolyte on the cap vents, ideally check the schem to ensure no bleeder resistors (these will need a limb lifting).
    Then remove the tubes.
    Work out where the rectifier output is (before the first filter cap) and break the line (either by removing the HT fuse) and insert a 100k 2w flameproof resistor.
    Switch amp on and then clip a volt meter across the resistor. Initially the voltage drop might be 200v dc but, depending on the state of the caps it will drop to 50 or 20v within 30 mins and, over the next few hours to 10v and if you are lucky down to 3 or 4v which means they are pretty perfect.
    If you do not get down below 10v then you will need to consider that the filter caps (or at least one of them) are not good enough to reuse and the amp will not function properly without replacing them.
     
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  14. ampmadscientist

    ampmadscientist Well-Known Member

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    Start the reactor... Free Mars!
    Yes there are amps w/ the original caps and tubes, and they do play but not frequently or often if they are "collected."
    If you play the amp all the time then it is inevitable that tubes and caps will eventually need replacing.
    You will either "collect" an amp or play an amp. But it's 2 different things. You don't want to beat up your old plexi by taking it out on the road...
     
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