Thinking about doing some ellicit things to my vintage Marshall...

Discussion in 'Amps and Cabs' started by michael.e, Feb 27, 2009.

  1. michael.e

    michael.e Supporting Member

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    So, I have two JMPs. This '70 Super PA breaks up WAY earlier than my regular JMP. I like that about it, as it makes it different enough to justify keeping, sort of... The one thing that I would like to change though is the character of each of the inputs.
    I have four pair of the same inputs. I was thinking of having two of the pair respond like a regular JMP, with the brite and normal inputs. I would love to have the other pair respond more like a Superbass setup.

    What do you think of my doing that? I am torn on this because of the vintage nature, but I really want to be able to use it more than I do. One of my rules is that no matter how much I love an amp, if I am not using it, it goes...
    I want it to stay, I love the amp, but I want it a tad more versatile..

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  2. LocustXReign

    LocustXReign Member

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    I wouldn't mess with her, that's a really cool piece.

    If you do sell it, please hit me up with a PM as Id like a shot at it!

    -DB
     
  3. re-animator

    re-animator Senior Member

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  4. stoob0t

    stoob0t Member

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    Im going to be a bad influence here. If you're only changing one of the four pairs of inputs, what's the harm? You sound like you know what you're doing, so you should have no trouble returning it to stock should need be.

    I'm of the belief that it's okay to do whatever feel fit to your gear if it makes it more enjoyable and playable for you. You only live once, and life's a bit too short to deprive yourself of fun just for the sake of the resale value of something. Also, if the mod works how you hope it will, the resale value wont be relevant anyway as you wont want to sell it!
     
  5. rob2001

    rob2001 Member

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    I'd exhaust all other possible tonal options before messing with a vintage piece. The thing is, there is no garantee that what you do to it will give you the desired results.
     
  6. RussB

    RussB low rent hobbyist Silver Supporting Member

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    Mess with the factory solder connections and watch the value drop.

    Sell it and get a good clone, like a Metropolous
     
  7. jackaroo

    jackaroo Member

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    If you want to tweak the circuit a bit I would suggest getting a tech who'll take the time with you to go through the board with a set of alligator clips and auditioning the new components one at a time. If you change everything at once, it's hard to pinpoint what did what and what you like etc. I had this done a few times- very cool and educational.

    I think you owe it to yourself to have what you want out of gear...but do it responsibly. I don't think you have to be too precious with the head, it's been retolexed and isn't a super rare plexi or some crazy historically important amp. So have at it. Just take note of the changes so anyone can put it back to stock should you want to sell later.

    Looks like a fun set up.

    One question, why is a 50 watter labeled as a Super? I thought the "Super" moniker was reserved for 100 watt heads, no?
     
  8. Relicula

    Relicula Member

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    Michael, if the serial number ends in "C", its a 71. Not that its a big deal,but thats what it looks like

    These were never intended to be guitar amps, but definetely do the job well. I would try bridging the different inputs and see if it gets you closer to what you want to do. More importantly, it is what it is, and should you decide to go the modification route, you probably will be less likely to achieve what you want.

    I would ask at the plexi palace, guys like clay finley, hamilton, and others are very knowledgable, and would be able to help, also do a search or post a thread asking other P.A. owners their experience on doing the things you are interested in.

    If it were me, I would put in the best tubes I could find, a good pedal or two, and fire it up to about 8, and see what happens.
     
  9. Lavely

    Lavely Silver Supporting Member

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    Given that it is already recovered, I don't see too much harm in a very non-invasive, easily-put-back-to-stock mod.

    Lavely
     
  10. Mastervolume

    Mastervolume Member

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    Hey Michael!

    you have a good chunk of a super bass there already.

    Splitting the cathodes on one of the inputs wouldn't be that big of a deal but would add gain.

    The tone stack is already bass values with the 56K 250pf and you have the .1ufs in the PI.

    You can change the front a bit on each input, add gain/subtract gain but I think that they would be subtle improvements compared to devaluing the amp.

    If it were me I would have a tech install a bulgin power jack on the back like the originals and then make you a cord that works for our sockets. The power cable into the back is just asking for trouble. Then I would leave it alone. Actually I would sell it and buy what I wanted.
     
  11. FrankieSixxxgun

    FrankieSixxxgun Member

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    Do NOT modify that amp, dude! What are you thinking?
     
  12. 908SSP

    908SSP Member

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    I wouldn't modify that board with its perfect solder joints. If it had been modded before that would be different. You can set up a a/b/c pedal with the gain happening after the pedal and run that into the front on different channels to widen your tonal possibilities. I run one input at 5 and the other at 10 that alone makes a big difference



    I have some Bulgin AC sockets and plugs to fix your power cord. ;)
     
  13. soldano16

    soldano16 Member

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    Go for it. Save the parts you take off.

    Enjoy the amp for what it's supposed to be - part of your creative process.
     
  14. michael.e

    michael.e Supporting Member

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    Thanks for the replies guys! When I got the amp, one of the Bulgin socket pins was broken. I have a replacement already, I simply have not installed it yet. Since I rarely move the amp, I am just being lazy.

    Along with the broken pin, one of the large silver capacitors was broken on the leg as well. I had to re-connect that. Now the board is not perfectly untouched. That was also one of the reasons that I was thinking of doing this..
     
  15. Ronsonic

    Ronsonic Member

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    Simple, respectful mods that can be reversed make perfect sense if it takes a good amp and makes it great. These are not bad mods. We're talking about a couple of cap and resistor changes that are easily reversed. Hell stick the old parts in a baggy and tape it inside the amp.

    Do it.
     
  16. cugel

    cugel Member

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    yeah since its recovered there is no harm in changing resistors
    i have a 68 50 watt pa and its all original and i am considering doing the same thing
    those are non invasive mods and i cant imagine a knowledgable buyer would be scared away by those mods
     
  17. 908SSP

    908SSP Member

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    Then you imagine wrong. But hey that makes mine that much more valuable. Go for it.
     
  18. doctord02

    doctord02 Member

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    I say it's your amp and you arent drilling holes in the chassis or other such nonsense. It's a tool, not an Egyptian Artifact from the Pyramids. Tweak it so it's useful. Just keep the parts and document what you do, before and after.

    I can see I'll get tarred and feathered by this crowd, but hell - I'm not *selling* you my JTM-100 Super PA, I'm keeping it me for *me*.

    I had Don Butler (aka Tone-Man, in Los Angeles) recap it and tweak 3 of the 4 channels into different era - but Marshall correct - variations; A Super Bass, A Super Lead Plexi, and a metal face era Super Lead. And one is a stock Super PA channel. Now I have four killer, useful channels. And if my heirs want to sell it - I have a ziplock baggie with about six resistors and caps in it.
     
  19. stoob0t

    stoob0t Member

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    It's hard to say this without sounding a little like a troll, but it disheartens me sometimes how there are so many people on this board who care far more about how much gear is likely to be worth in the future, than it's owner getting more enjoyment from it.

    I say, do what you like to your amp - make it yours! I know it's an extreme example but no one seemed to stop EVH having his Marshalls modded because they'd be worth more in the future.
     
  20. mesanatic

    mesanatic Member

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    My first thought also, on the Super designation, but the 50w PA's are either a 2 channel/4 input model 1985 (PA version of 1987) or 4 channel /8 input model 1963 Super PA as this one is.

    I'd leave it alone but, you want to try it why not. It's been said the amp isn't very valuable, especially now, so preserving it isn't going to get you alot more.

    On the other hand most PA's have been modded so your's does stand out.

    Plus if you mod one channel it may very well affect all the channels and you know you like it as is.
     

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