68' SuperBass Lost Its Mojo : Marcon 40-40 PI Goes Bye Bye. . .

Discussion in 'Let's Talk Vintage' started by JTM 100 Mk V, Sep 18, 2020.

  1. JTM 100 Mk V

    JTM 100 Mk V New Member

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    Greetings From Toneville everybody ,
    Well my beloved 68 SuperBass developed some noise and an overtone that was ugly, so I shut it down and put it on the bench. I immediately noticed a bulge in the PI cap. I've been pushing my luck on the caps I know, but the tone has been to die for while in my care and I've kept a close eye on things. So I had an F & T 32/32 on hand and performed the swap.

    This amp sounded remarkable, VHII and WACF tones all day long into the matching cabs with 25's. The remarkable tone factor here was the spongey bouncy bottom end. Tight, not stiff. Very elastic yet dynamic.

    With this F & T, the mojo just went out the window. I've got more volume and high end with stiffness. Noticably stiffer.

    I get the fresh cap sound, I've recapped and built stuff where I've heard it age and break in over time.

    Thats now what I'm hearing. Radical tone variation.

    So, first reaction is . . . Where can I source NOS Marcon 40 / 40 Filters ?

    From there I am all ears, I've never had this radical a change from one filter or part thats within spec.

    I don't believe the F & T is bad, in fact quite the opposite, Its very healty. I don't think a 50 / 50 LCR would be the answer either. So it leads me to ask about the Marcon here. Was it "THAT" good ? Was I only operating on half of the cap to begin with ? I only measured the UF when it was out and drained, and it speced ok ... 41 / 42 actually.

    I'm a little confused and could use some advice here.

    Thanks alot in advance and I look forward to getting the groove back. I'll include pics :
     

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  2. Matthews Guitars

    Matthews Guitars Well-Known Member

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    NOS caps are sure to be bad at this point. The absolute worst thing you can do to a capacitor is store it for long periods of time in a discharged state. When that is done, the internal electrolyte actually attacks and destroys the anodization layer on the aluminum plates. You MIGHT get lucky and be able to reform such capacitors for a limited service life, but they're never going to give a full service life.

    The elastic bottom end you liked so much is a consequence of the capacitors ageing and developing higher ESR, higher leakage, and probably reduced capacitance values as well.

    It's like saying you like the ride quality of worn out tires. Which you probably can't duplicate with fresh rubber, but who wants to put another set of worn out tires on?

    I don't know how you can get that "old cap feel" once your old caps have failed.

    Are the main reservoir capacitors original, too, by chance? If one has failed, the others can't be far behind. The consequence of failure could be as high as a killed power transformer.
     
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  3. william vogel

    william vogel Well-Known Member

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    Run the new cap at 32uf only vs 64 and see if it adds a little more bounce to the amp.
     
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  4. JTM 100 Mk V

    JTM 100 Mk V New Member

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    Thanks for the insight. Thats the situation I'm in exactly.

    The whole amp is stock so this day was invevitable. I still have the Hunts 100/100 and the Daly 32's.

    So I guess next question would be regarding favored replacement brand. I've got Sprauge on hand and would Guess F & T would probably be good as well. I've also seen the JJ and CD that seem to be the former Mallory co.

    I'm open to suggestions , I really appreciate the advice.
     
  5. JTM 100 Mk V

    JTM 100 Mk V New Member

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    Thanks, thats a good idea. I was thinking about that Marcon running on 1/2 the cap and was scratching my head. If it turns out to be the actual situation as you describe.

    Tomorrow I can get under the hood and turn it up. so I'll report back !
     
  6. Matthews Guitars

    Matthews Guitars Well-Known Member

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    F&T caps are as high quality as anything you can find today, that fits the requirement.

    Earlier this year, I was in talks with Kemet, the company that owns the rights to all the Daly capacitor brand, about reissuing correct Daly capacitors for restoration purposes,
    and they were looking into doing this. But I don't have any updates on that. I do think it's be nice if they were to offer cosmetically and functionally correct capacitors for those
    of us who are such traditionalists that we want our capacitors to be blue Dalys. Maybe it'll happen.

    If it does, quality will be assured. Kemet makes caps that are second to none.
     
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  7. Dogs of Doom

    Dogs of Doom Moderator Staff Member

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    you can try these guys...

    https://hayseedhamfest.com

    they make custom cap's & someone said they had them rebuild/restuff old cap's.
     
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  8. South Park

    South Park Well-Known Member

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    The caps and choke work together to make that surge sound . So what’s wrong with the 50/50 caps that it came with . That 32/32 may not match up with the choke the same
     
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  9. Dogs of Doom

    Dogs of Doom Moderator Staff Member

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  10. Matthews Guitars

    Matthews Guitars Well-Known Member

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    That's a 50 volt cap. It'd explode very quickly.
     
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  11. Dogs of Doom

    Dogs of Doom Moderator Staff Member

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    450v...

    upload_2020-9-18_20-31-8.png
     
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  12. Matthews Guitars

    Matthews Guitars Well-Known Member

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    The page you linked to has a typo then. It does say 50v.


    captypo.jpg
     
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  13. neikeel

    neikeel Well-Known Member

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    Sadly I have experienced this tone change with new caps myself. This is why I try to preserve the originals by reforming and am prepared to try to reform NOS caps (but I emphasise only use them if they reform to spec)
    Mostly you have to replace with the best available modern replacements, which, I agree are F&Ts. The tone benefit can also be positive too, but typically in more modern higher gain amps
    I find the optimum PI cap in a 12 series to be a 32/16 parallelled to make 48uF. But trying just the 32 on its own may point you in the right direction. Funnily enough the screens being replaced on these can be even more dramatic...............
     
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  14. junk notes

    junk notes Well-Known Member

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    I am looking for axials for a 68 layout. I have been tempted to get these very high quality made, but are for a (Macintosh, H.H. Scott, Marantz, Kenwood..) stereo's power section. An audiophile cap is considered clean for best signal and low noise distortion, but sterile for a guitar amp. Will they be too stiff, or sound non musical?
    I have not tried the JJ axials, so leaning to that because I am not familiar with axials other than that of the electrolytic cap(s) on preamp board.
     
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  15. boola1

    boola1 Well-Known Member

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    I would describe F&Ts exactly the same as you. Try a Mundorf instead, a warmer and richer tone IMHO. I use them whenever I have to re-cap and never worry about my amp losing it's mojo. In fact, it normally sounds better.

    https://www.hificollective.co.uk/catalog/mlsl5002020-32uf32uf-500v-mlytic-radial-type-p-1398.html

    EDIT: Oh no! They have been discontinued :( :( :(
     
    Last edited: Sep 19, 2020
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  16. Dogs of Doom

    Dogs of Doom Moderator Staff Member

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    yep, cap's have become stupidly ridiculous to find these days...
     
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  17. Matthews Guitars

    Matthews Guitars Well-Known Member

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    Well, the call for high voltage capacitors is greatly reduced these days compared to the days where having other equipment in your house that contained vacuum tubes was an ordinary, everyday thing. TVs contained tubes (other than the picture tube) into the late 60s and even into the early 70s. So the supply and selection has to be limited these days. Just be glad that there is adequate demand that we usually have a choice of suitable parts.

    If you think that there are capacitor needs for Marshalls that aren't being properly met by any existing products, then you might send an email to Barker Microfarads, Inc with your capacitor requirements. They're the former USA Sprague Atom factory, with former Sprague employees using former Sprague tooling, and they make top quality capacitors and are the prime provider to Mesa/Boogie for their high voltage capacitor needs.

    If you were willing to speculate on the market, and spend some money, BMI could make you a run (a certain minimum quantity is required) of the capacitors you need, you buy the whole lot, and retail them to others for a fair profit. They can certainly make capacitors that meet your specifications.
     
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  18. JTM 100 Mk V

    JTM 100 Mk V New Member

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    Ok, sorry for the delay on the update. I decided to not trust my first impressions, dug up an old recording and decided to set up for a comparison. Before I did this however, I had literally no burn in time with this cap so I took it to jam and brought a tube screamer and wah.

    The first thing I realized was I had way, more, and I mean WAY more interactive tone controls. No more of just ' dime it and go ' . This amp was in the box for years untouched because of the tone so I was dealing with 'ol reliable.

    I plugged into VI Initially and it was where I got my bright , stiff and missing mojo feeling from the start. So I plugged into VII and things were more familiar .So I figured I would just start fresh and bring up a familiar tone juice it a bit with the tube screamer and be good.

    And so it was. I could hear the burn in as we played believe it or not. We had just a three piece going and I had extended high end and dynamic range. i also noticed the bottom end get organized as we went on and the shimmer started to come back. Its a harmonic rush that is just so gorgeous. Its coming back.

    So here I paused and checked out VI again and just went straight in. I adjusted the tone controls and Presence that actually worked better now and pushed it to the edge of breakup. Here is where things began to change for me. I could feel the extended dynamic and when I dug in I really got the crunch I was looking for. More dynamics and detail for sure. Much towards a Hi Fi type of thing. More than that new tube feeling.

    So overall I walked away with some new settings , more overall range and dynamics and a little more tighness. I found I had the bass rolled down and could get some more bounce and spring when I added it. Not like before at this point, but thats not bad considering.

    Now the payoff. When I did some recording of the tones I was very pleasantly suprised. My ears were right. As described above is what I heard comparing to the old golden recording tests and the core character of the amp remained.

    The thing I can confirm that makes it feel bizarre is that I could hear and feel more than I was accustomed to. We all know we are hanging our ass out when we play a NMV Marshall and this was a reminder of that FIRST time you felt it. I had to get really detailed with what I was doing, cause you can hear it all.

    That was a cool experience after the initial boo hoo. I dropped the pick for a while and I have to say that for clean tones , chime, ring and shimmer I'm left not wanting anything. And then like before just roll up the guitars volume into that amazing world of gain again.

    So I'm super relieved at this point. I'm still going to perform some tests. I have a good set of known caps that will allow me to test from 16 , 20 , 32 , 40, 50, 60, 64, 70, 82, 100 etc. Not that I will do all those values but as everyone suggested above I want to at least simulate half of the Marcon 40/40 and see how it goes for feel. If that bounce comes back with the additional frequency, I will have learned even more how this amp responds.

    Upon reporting back on that I have another amp to post about. It relates to a wiring mistake as well as for me 'the one that got away' amp. The simple PI cap really taught me a lesson here. More to come!

    Thanks again for everbodys help as I gently restore this beast.
     
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  19. Matthews Guitars

    Matthews Guitars Well-Known Member

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    Cool, and a nicely detailed report. Honestly I'm not surprised. Component break-in really is a thing. Remember, these old Marshalls literally were game changers when they were the new amp in the music store, so you must expect that they sounded very good and very lively when they were new. You've gotten back a large measure of that lively new amp sound now and I'm sure it's good.

    Yes, when I got my first Marshalls (two in a week), I quickly learned that they put the spotlight on your playing. You can't hide. Your sloppy technique is out there for everyone to hear. Or your excellent technique. Such an unrelenting critic of your talents can only help you to improve your playing. It SHAMES you into doing so.
     
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  20. neikeel

    neikeel Well-Known Member

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    That is really cool update. I guess your old caps were clearly on the way out. Couple of my best amps (that I kept after cap change) have either settled in, or I got used to them. I would love to have recorded clips before and after changes.
     
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