Recap My Plexi?

Discussion in 'Let's Talk Vintage' started by Trapland, Mar 5, 2019.

  1. Trapland

    Trapland Well-Known Member

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    My beloved ‘68 50 watt is ghosting pretty bad when cranked above 5. I really don’t want to change it’s overall character nor affect its originality if possible.

    Can these caps be dated?

    Can they be replaced with working NOS? Where from?

    Which is most likely to reduce the ghosting? First power stage right?

    (When in question, when in doubt, run in circles, scream and shout.)
     

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  2. neikeel

    neikeel Well-Known Member

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    That is an early 68 with those cans.
    I presume that you do not have the internal can for screens and PI that sits over the PT?
    If one can is failing (and these 50watters don't ghost in good condition IME) then it is probably good practice to replace them all, and the bias caps.
    I'm guessing the corner one is 16+32 linked for 48uF on mains and the other can is 32 for the PI and 16 for the screens.
    The preamp can is pretty rare and the nearest is a dual 32 from valvestorm, just check with him that it is a recent reform (date on the label).
    Alternative is go to F&T who still sell:
    https://www.tubeampdoctor.com/en/sh...TAD_Gold_Cap_33_33uF_450V_axial_capacitor_516

    https://www.tubeampdoctor.com/en/sh...0V_electrolytic_capacitor_radial_35x50mm_1182

    The above will be direct replacements, I think ARS still do 32/16 cans too.

    The amp will certainly be crisper and feel different initially, probably more like it was when new?
     
  3. ampmadscientist

    ampmadscientist Well-Known Member

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    " Can these caps be dated? "

    Yes, the date is somewhere before dinosaurs walked on this planet.
    And, there is carbon dating also.
    A newer technique is to date the layer in which the capacitors were found...

    " Can they be replaced with working NOS? Where from? "

    Capacitors go bad with age.
    I recommend you install fresh new capacitors.
     
    Last edited: Apr 28, 2019
  4. Trapland

    Trapland Well-Known Member

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    Or....maybe if you buy a few drinks?
     
  5. ampmadscientist

    ampmadscientist Well-Known Member

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    There's always carbon dating...
     
  6. Trapland

    Trapland Well-Known Member

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    @neikeel You are the best. Thank you.

    I just HATE the idea of changing anything. It’s not about the money or work, it’s about the beauty and tone. Arggg.

    edit: Yes, there is no can inside over the PT.
     
    Last edited: Mar 5, 2019
  7. TAZIN

    TAZIN Active Member

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    The two top side mounted filter caps (HUNTS 32uF - 16uF/450Vdc) date to May 1967. The TCC 32uF - 32uF/350Vdc preamp filter cap dates to August 1967.
     
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  8. proxy

    proxy Active Member

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  9. ampmadscientist

    ampmadscientist Well-Known Member

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    August 1967

    That was before recorded history.
     
  10. ampmadscientist

    ampmadscientist Well-Known Member

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    Start the reactor... Free Mars!
    You need to solder / unsolder anyway, might as well be new fresh caps.
    You can save the old ones.
    You will be surprised how much better it sounds w/ fresh caps.
     
  11. boola1

    boola1 Active Member

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    hmmmmmmmm



    I prefer Mundorf caps over the F&Ts. I find the Mudorfs have a warmer tone. F&Ts are quite spiky when new. Who knows what those Hunts sounded like when they were new?
     
  12. anitoli

    anitoli Well-Known Member

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    REPLACE THEM! They are as old as i am. Caps do not last forever so why try to make them last forever?
    Then again if you don't mind scraping out gobs of dried out electrolyte just keep running them, sooner or later one will explode.
     
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  13. Trapland

    Trapland Well-Known Member

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    I can’t do this. Not that I CAN’T, I just don’t want to. Right now (except for the subtle ghosting) it is the best sounding Marshall I ever had. The latest date I can find on it is 2 mustards that are A8s. Everything else is 1967(thanks @TAZIN). In my mind it’s pretty special.
    Honestly, unless I was willing to pay double it’s worth I doubt I could not find a more straight plexi in my area.

    If I could find reformed NOS Hunts from 1967, I would replace them. Without that, I’ll just put it into semi-retirement and use it for recording and the occasional fire up to keep it functional.

    This sucks. I can fall back to my 71 four hole PA which sounds excellent but different. It’s had some work done including caps so I don’t feel so bad doing whatever to keep it giggable. Maybe I can work at voicing the 71 to sound closer to my 68. 32/32 and 32/16 for a start? It already has split v1 and i’ve changed the tonestack to match. Thanks to @neikeel I have a great source for those cans.
     
  14. soundboy57

    soundboy57 Well-Known Member

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    I had a mint 1971 small box that ghosted badly even after I replaced ever electrolytic can in the amp. May have been able to cure it with playing with coupling caps, or some such, but I sold it.

    I replaced all the cans in a late '67 (and many others over the years), and it sounded even better.
    "Collectors" whoever that is, don't care about filter cans if the rest of the amp, especially the transformers,
    are original.
    Myself, I can live with some ghosting...they all do it somewhat, but if it is real bad, especially when you get the amp roaring
    at volume, it is no fun to play...so why keep the original (probably) dried out filter cans?
     
  15. boola1

    boola1 Active Member

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    It's the best sounding Marshall and yet you are semi-retiring it. That just makes no sense to me. I couldn't get by without my fav. Marshall.

    If you reduce the amount you use it, the filter caps can only get worse. Soon you wont be playing it at all or one of the caps might pop and cover the board in horrible goo. You might as well just sell it now.

    It doesn't have to suck. Just change the electolytics and enjoy your amp!
     
    Last edited: Mar 7, 2019
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  16. Nik Henville

    Nik Henville Well-Known Member

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    Quite possibly the most sensible post I have read in my short time in this crazy forum
     
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  17. GIBSON67

    GIBSON67 Well-Known Member

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    Is there a way to determine which cap might be causing the ghosting? Piggyback another cap for testing?
    Or do you have to pull the cap and check it out of the circuit? Obvious signs of bulging, leakage etc...easy to spot.
     
  18. Trapland

    Trapland Well-Known Member

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    You need not agree with me but I want to justify my idea.

    If I change caps this amp WILL sound different. It very well may not be my favorite afterward.

    I believe regular use keeps caps operational, but excessive use shortens their life. ‘Soon you won’t be playing it at all”. Really? How soon? The caps are 50 years old and just barely showing signs of age. How soon? 5 minutes? Or 5 years? I’d be willing to bet the health of MY amp that it’s closer to 5-10 years.

    I’ve pretty much always played vintage amps. I also play them dimed most of the time. Some I’ve owned for 15+ years. The ONLY catastrophic cap failure I ever saw was a modern cathode bias conversion experiment that was underrated. Yes it was a mess, it was stupid to use it. (I was young and green).

    I think cap explosions are incredibly rare. And sudden cap failures are too. Do they happen? Hell yes. But a more likely scenario is ghosting just gets too forward, or hum is excessive, or noise, or bias is hard to lock in, or a tube starts overheating. Then you HAVE to fix it.

    I know enough to know when service MUST happen. Then I’ll do it. Now that I know I cannot get the NOS parts I’m over it.

    I don’t see the need to preemptively devalue my amp and change it’s tone with a cap job that can be put off for years.
     
  19. anitoli

    anitoli Well-Known Member

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    Why do people start threads asking about recapping an amp then argue against it? Do what you want it's your amp i could care less at this point.
     
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  20. boola1

    boola1 Active Member

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    You started this thread because your amp is 'ghosting pretty bad'. Yes it will sound different, it will sound better.

    Anyway, what's to stop you putting the old knackered caps back in?


    It wont devalue your amp. I had a 67 that was all original. I changed the caps and then sold it for more than I paid for it.
     

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