What Mods do you have on your Marshall head?

Discussion in 'Marshall Amps' started by JCMRobbo, Jul 21, 2020.

  1. JCMRobbo

    JCMRobbo New Member

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    I’ve seen a lot of videos and bits and pieces of people Modding their amps usually JCM800s or old SLP/87x and various other Marshall icons to be likeSlash’s #34. With the extra valve.

    I’m interested to hear what you people have done to your amps and why you’ve done it. I love my JCM 900 but I’ve had it for a long ass time and I’d like to know if any of these mods are possibly universal to any Marshall amp. Kind of make it my own.

    modding isn’t just electrical it maybe visual as well.

    so let’s see and hear what you’ve got!
     
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  2. Filipe Soares

    Filipe Soares Well-Known Member

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    2203KK - Zero Loss FX Loop and a Choke. I'll probably do a depth knob very soon

    Major - one wire mod (switchable) and a master volume.
     
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  3. junk notes

    junk notes Well-Known Member

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    Soon, there will be plenty of mod's to try on the SV20H, and that would include an attenuator and a variac for some additional fun. :)
    Shortly following there will be the JCM800 1w mojotone clone into a repurposed 1x12 combo (JCM 4010). The first mod will be attenuating the speaker out. So there will be an output level parallel to the volume and master volume, if that makes any sense.
     
  4. BftGibson

    BftGibson Well-Known Member

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    1987 is now 2204 with TW 3 PPIMV, hoffman board

    jtm45 has 1966 Fender Bassman power w/6l6 tubes, PPIMV

    Have 2 fantastic tech friends, both been doing it since the 70's. 1 Fender & 1 Marshall who have tracked values over the years & we dial em in to what i am looking for.

    My Fenders are really set up nice.
     
  5. EADGBE

    EADGBE Well-Known Member

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    I have four Marshalls and none of them have been modded.
     
  6. IOSEPHVS

    IOSEPHVS Well-Known Member

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    No modifications here, unless you consider that I'm running Mullard EL34s and CV4004s, instead of stock Svetlana EL34s and Shuguang 12AX7s.
     
  7. K2JLX

    K2JLX Well-Known Member

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    Stock all the way on my lot apart from an i63 Mullard ecc83 in the Sv20h V1 socket.
     
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  8. MonstersOfTheMidway

    MonstersOfTheMidway Well-Known Member

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    sorry, no mods to talk about in my stuff.
     
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  9. marshallmellowed

    marshallmellowed Well-Known Member

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    After years of modding my amps, I finally came to the conclusion that, if you spend more time modding an amp than playing, you've got the wrong amp. Otherwise, you must like tinkering more than playing. I only do minor tweaks these days.
     
  10. mickeydg5

    mickeydg5 Well-Known Member

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    I wondered about the big 470R instead of a choke in the 2203KK. What choke did you go with and what is the DCR specification?
    How do you like the choke over the big 470R dropper resistor?
     
  11. South Park

    South Park Well-Known Member

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    I have one 2204 withe the Hendrix Tone stack mod . A 2204 with a gain mod on v1 . And a soldano 50 clone with fender transformers . Thar are no mods we just build them that way.
     
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  12. El Gringo

    El Gringo Well-Known Member

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    I have 2 bone stock 2555X's
     
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  13. johnny q

    johnny q Active Member

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    I have a 1972 Super Lead (and it's a "Rosemary!") The seller told me it has the "Rich Mod." I know of this mod via the internet chatter. But here is how my particular mod works:

    The 4 inputs have been modified so that only the top left high input works. Volume 1 knob is overall volume and Volume 2 knob is "gain" So in that respect, it works just like a regular master volume amp.

    The problem is, to get the tone I like, I need to turn both volume knobs to around 7, which is insanely loud! If you crank the gain and keep the overall volume low (i.e. "bedroom" volume) the sound is thin and unsuable. SO, I am wondering if I should just have the amp returned to bone stock, if I have to crank it anyway?

    My only hesitation - I don't know how much this mod is attributing to the overall tone of the amp, which I really like. I would hate to de-mod it only to learn I liked it better before.
     
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  14. Filipe Soares

    Filipe Soares Well-Known Member

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    I don´t know if I did it right, but after some long talks to a friend who´s a amp tech he suggested to me using a 3H, which is around 115R, he said to me that the voltage might raise a little bit but with it would cause no harm. What are your thoughts about it???

    The amps is different, for my taste it sounds better. But I´m a novice regarding amp mods and I have to ask you guys who know much more than I do.
     
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  15. scozz

    scozz Well-Known Member

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    None.
     
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  16. Eddie78

    Eddie78 Member

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    Has anybody tryed the R6 mod on JCM 800 lowering resistor from 10 to 4.7 k?? Does It works? It's a very simple mod to increase gain I'd like to try
     
  17. GIBSON67

    GIBSON67 Well-Known Member

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    @Eddie78 all you have to do is piggy back another 10k resistor to the one on the board and then you'll have effectively 5k with no mods.
    If you like it then solder it that way, otherwise just take it out.

    I have a hand wired hot-rodded 2204 at the moment. I lowered the voltage into V1 and with different values. I've had it as a 1987 with PPIMV,
    1987 with OWM, and stock 2204. I really like the MV on the 2204 and not the PPIMV mainly because I like to keep my Presence knob.
     
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  18. Geeze

    Geeze Well-Known Member

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    A friend built me a 1987 with PPIMV as an experiment - I go back and forth on using it depending on mood. The other 'modded' amp is a 77 JMP2203 [EL34] that has an OT from a Hiwatt - I guess the original blew up. It has a 'singing' quality that a 78 JMP2203 [6550] doesn't have yet it sounds great in it's own way.

    I'm a big fan of figured wood cabs!

    [​IMG]

    Russ
     
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  19. mickeydg5

    mickeydg5 Well-Known Member

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    3H is the norm but there are 5H up to pass 20H.
    The specifications give details and indicate the DCR while any choke made with more winding, especially the larger H's will have higher DCR.
    So a high wound or larger choke can have 470 ohm DCR and drop volatge like the 470R power resistor but the choke does more energizing and holding the voltage that is there more steady when current demand changes. A plain resistor will not d that and the voltage just free falls on high current demand.

    Now the average 3H probably has 115 DCR and most like that level since the the B+ stays a bit higher and you get the advantage of the choke characteristics. But I have played decent amplifiers that had a 100R or so power resistor and actually like that value because it had a good feel and sound, not dropping the B+ so much.

    You do not see a 470R in the B+ too often before the screen connections. That is why I wondered how much of a difference it made used that way compared to other lower values or chokes.
     
  20. Filipe Soares

    Filipe Soares Well-Known Member

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    I had to takeover our operation in a different state here in mexico, so I´m 4 days at home and 4 days in the Port. I did the choke because it was a ¨quick¨ job, but I´ll be honest with you I didn´t measured the changes in the B+ currents. I was so fucking curious about any change that would come from the mod that I just did it.

    I´ll return friday and it´s quite likely I´ll manage to install a depth knob in the amp, I´ll take advantage of the disassembled amp and measure it.

    The amp has changed, a lot. It was not a subtle change, it was something that you can notice very quickly. The whole low end is different, its tighter and clearer. In a general way the amp sounds more like a marshall. I´ll keep playing it for a few more hours and make my conclusions after that. If I have the chance I´ll record something. Recording using IRs would be very easy, because in higher volumes the amp is sounding totally KICK ASS, but my neighbours won´t like very much a ¨evening recording with a 2203kk ¨. Let me see what I can do.

    again... this amp is very underrated, it can do much more than Slayer.
     
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