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MARSHALL GAIN Why does a 1972......

Discussion in 'Amps and Cabs' started by Tag, Apr 30, 2005.

  1. Tag

    Tag Gold Supporting Member

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    have so much more than later 70s Marshalls? Both myself and a friend had 1972 50 watters, and they both SMOKED! LOTS of gain, almost right off idle. I had many other 70s Matshalls, and none had anywhere near the gain of those. What was it in that circuit that gave them extra gain, and why did Marshall reduce the gain in later years?
     
  2. ericb

    ericb Silver Supporting Member

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    I've wondered that as well from reading this internet stuff as my 1971's are nothing like these 1972's are described!!! Shea or Clay or Doug or some other Marshall techs should know???? ERIC
     
  3. carlygtr56

    carlygtr56 Guest

    Probably an ear-piercing bright cap value
     
  4. tralfax19645

    tralfax19645 Member

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    Hi,
    One reason would probably be the .68 mf cap bypassing the 820ohm resister on the voltage amplifier half of the 2nd preamp tube. Some models had em some didnt. That cap adds a lot of gain.
    Rob
     
  5. VaughnC

    VaughnC Supporting Member

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    Yup, I agree....most likely the right value cathode bypass cap(s) in the right place(s). That is one of the infinite number of variables that can make a guitar amp awesome or a turd.
     
  6. Roccaforte Amps

    Roccaforte Amps Member

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    The 50watt models run lower voltages,
    and require higher bias settings
    to produce full power.
    Because of this they distort much earlier,
    its not a matter of "more gain".
    Doug
     
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  7. Tag

    Tag Gold Supporting Member

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    Doug,
    They have way more gain. Its not just earlier. I had many 50 watters. The 1972s had far more gain even when wide open. Its not even close. To do even the hardest rock back then I needed no overdrive pedals.
     
  8. IPlayHamers

    IPlayHamers Member

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    I have a 72' 50 watt and can attest to it having gobs of gain. When i bought the head a few years ago, it had been modded with a post PI master volume. I haven't changed a thing. Most people think it has a added gain stage, but when I let them see the back of the amp the usual response is, "Oh My Gawd!!!". It can sound very modern with a eq pushing the front end and with my Xotic AC Booster it can easily go into meltdown.

    I always loved that edge of destruction sound you get with some amps and this one has it in spades.

    Someone above mentioned Germino? I just sent him an email asking if he would duplicate this Marshall for me. Can't have too much of a good thing is my motto.

    Paul
     
  9. tmac

    tmac Goldmember Gold Supporting Member

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    Yes, and I think even some had even higher like a 220 uf - I've read where EVh magic Marshall had that. (I've set my amp up with a switch to bring a .68 uf it in and out, it does add quite a upper mid boost). Another thing would be the feedback resistor and what tap it goes to. Some had 100K and that will be hairier than 56 or 27K. And maybe the plate resistors have drifted up. And like Doug R said voltagewould need to be measured. Could be a lot of things, but I'm sure one of the amp builders could make a real close to a copy if they could take a look at the amp and measure some things.
     
  10. ericb

    ericb Silver Supporting Member

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    Hi SHinrock , are you referring to my 1971's I was posting about? IF so , yep I know.. I have a quite-modded 1 now, but I had a much more stock one in the early 80's. That one was absolutely awesome. BuT you'd never call them a hi-gain amp without lots of mods.. Are the 1972's that Tag's referring to JMP's ? And are they JMP's with resister changes from the 1974's on , or other circuit changes ? Also are you a builder or tech , as I've enjoyed your posts .. Thanks

    ERIC
     
  11. JTM100

    JTM100 Member

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    I have a '69 SLP that is like that. It is bone stock and gets about as much gain as a DSL without the "buzz". I owned a '72 50w some years back. It definitely had more gain than average. But not as much as my '69 100w. However, I have owned and played MANY vintage Marshalls and have yet to find one that does have as much gain as my '69. I have spec'ed it out and there is really nothing out of the ordinary component wise for the time period. I am thinking that it is all in the sum of the parts with thier various tolerances as opposed to one single cap or resistor. As far as '72 50watters go, has anyone done any indepth comparisons between that year and '71 or '73 to see if something was changed? Marshall seemed to like to do alot of thier R&D in the field.
     
  12. John Phillips

    John Phillips Member

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    Component variances do play a part, definitely. Most of the resistors used were 5% tolerance, and the caps 10% or even 20. Normally, the variances average out to some extent, but some positions are more critical than others, and you can get the odd exception which sounds quite a lot different from the normal range.

    There's also the possibility of wrong component values - check the resistor color bands very carefully, or meter them. I've come across a very small number (but more than one) of apparently stock MV models with the second-stage cathode resistor being a 1K not a 10K - this massively increases the gain. It's hard to say whether the assembly workers were just using some from the wrong bin, or whether they were supplied wrongly - the difference between the red and orange color bands can sometimes be quite slight.
     
  13. tralfax19645

    tralfax19645 Member

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    Looking at the shematics in the GT book,the 1959 (100 watt) and 1987(50 watt )models that used el34s and NO master volume used the extra cap across the 820(1K) cathode resister on the voltage amplifier half of the 2nd preamp tube. On the amps that used the 6550s (MK 2) this cap was eliminated,and a different value of R/C on the presence circuit was used. All of these amps have a date of July 1970.
    The master volume model schematics dated 11/76 also has this cap eliminated. Other than the master pot itself, this is the only difference I can see in the preamps . The ones with the cap would have more gain.

    You can look it up yourself.
    Rob
     
  14. Tag

    Tag Gold Supporting Member

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    I am not one who believes in the parts tolerence thing. I have owned and played SO many from the same years, and as far as I am concerned, they all sound EXTREMELY similar. No more different than 5-6 of the same HR Deville or DSL of today. One may be a little brighter or darker, and have a little more or less gain, but thats it. If someone stumbles on and old one that had WAY more gain than a different model of the same year, I believe it was modded. There was SOMETHING different about the 72 50 watter on every model, and the 71s did NOT have has much gain. Neither did the 73s. It is also talked about the Marshall book. My 72 was a small box, with the small "Marshall" logo. As far as I know, Marshall did not make MVs untill much later than 72. If I can ever find my old cassettes of our band at the time, I will post some clips of it. It simply screamed. The clean tones however wre useless and pretty much non existent
     
  15. John Phillips

    John Phillips Member

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    What I was saying is that component variance is real, just as it is on modern amps too. And it affects the tone, and to some extent the gain.

    I doubt it's responsible for a drastic change in gain though - from what you're describing, it sounds like a factor-of-ten change or something like that. That is much more likely to be a deliberate circuit change, or a wrong value component, than the 5 to 20% change that an end-of-tolerance component would cause.

    I can't see anything in the schematic that should indicate that large a change, and from memory none of the '72 Marshalls I've worked on (out of at least a couple of hundred old ones) were really out of the ordinary - just within the normal range of variance.

    So I'd be more likely to go for the 'wrong value' option. I don't know which component. I used the wrong-value resistor in the MV amps as an example - it won't be the same one in the '72 50W since that value is different anyway. It's not imposible that it only affected a particular batch of amps (maybe even an export-only batch), either - and I just haven't come across one.
     
  16. Tag

    Tag Gold Supporting Member

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    That could be, but both myself and another guitarist had them, (72s) and they were pretty much exactly the same. Not sure if the serial #s were close or not. In total amout of gain, I would say maybe 20% more than a Trainwreck express if you have ever played one of those. I had always heard they were like modded Marshalls, and to me, it was like a weak version of my 1972.
     
  17. michael patrick

    michael patrick Supporting Member

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    I think it's the chicklets they used in place of mustards...;)
     
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  18. JTM100

    JTM100 Member

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    All I can say is that my '69 is NOT modded. Vintage Marshalls are not really all that complex so any mods would be pretty easy to spot. Plus the amp has been checked by a tech who is more than qualified.

    John,

    You may be onto something with the "wrong values" theory. "It may also be possible that whatever supplier Marshall was using for resistors could have sent them either some mislabled ones or some that were way out of tolerance. I would imagine that by '72 Marshall was purchasing capacitors and resistors in pretty large quantities. I doubt that they took the time to measure each and every one. If they got a batch that was out of spec, that could explain the reason for the '72 50w gain. However, since the '72 50w seems to be the only one affected from that year, it would have to be a componet value that was either used only in the 50w and not in any of the other models or a componet value that was used in all models but only in a maximum gain affecting positon(s) for the 50w. Ideally, it would be great if someone could get hold of a '72 50w that has the high gain qualities and conduct some componet measurements. I owned a '72 50w and Tag is right, something changed. If everything on a '72 looks the same as a '71 or '73, then it would be reasonable to assume that there is something in there somewhere that may look the same but apparently isnt the same.


    Michael,

    I dont think that Mustards in general are the factor. My '69 100w has Mustards and as I said earlier, it is a gain monster.
     
  19. Ian Anderson

    Ian Anderson Supporting Member

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    I have a November, 1971 50 watt thats a monster!
     
  20. guitarjb44

    guitarjb44 Supporting Member

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    I have heard that the real difference which makes the '72 Marshalls seem more "gainy" than other years is that they switched from audio taper to linear pots (or was it vice versa...?) for a time in '72.

    Anyone else ever heard about this?

    -Joe
     

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