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1988 Silver Jubilee 25/50 Anniversary Head

Discussion in 'Marshall Amps' started by 67Mopar, Apr 7, 2019.

  1. jupiter89

    jupiter89 Active Member

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    In regard to the different SJ circuits, the truth is VERY likely that serial numbers after 03100 had the improved circuit. There was a tread in Dec 2007 called "Different Jubilee circuits???" Why is it very likely true ? Well back then the guy who started the thread posted the schematics officially from Marshall that looked like a blueprint which addressed the revisions. At the time I took a lot of notes, but for some unfortunate reason could not download the picture of this intial circuit vs. the revision. If you go to the original thread you can see the link is there to click on but it leads nowhere at this time.

    What I can tell you from my notes is that Marshall's official blueprint stated "2550 STD Also 2553 & 2558" for their initial circuit, and below that was the revised circuit that said "Models 2550, 2553, 2554, 2558" AND "USED ON MODELS WITH SERIAL NUMBERS 3100 ---->" ! ! !

    Whoever posted the link added his note on the schematic "schematics from marshallschematics.com" Like the the link on the old thread mentioned, this URL does not work either but asks for a security check - don't feel comfortable going further.

    Hope that the pictoral schematic comparison is out here somewhere and that this post helps in some way. Earlier I thought from years back I actually had the picture, but I searched and only have only the notes I took on my newer PC. Gotta kick myself for not saving the pic I had. Gonna do a little digging and see if I can locate the schematics on a site other than the one above.

     
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  2. 67Mopar

    67Mopar Well-Known Member

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    Did you clean the new jacks? I know that may sound goofy, but production lubricants can cause the same problem. Lead-free solder can be a pain in the ass as well. If you don't get it hot enough, you can end up with cold joint(s). I run my iron at 750 degrees with lead-free, 700 with tin/lead.
     
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  3. 67Mopar

    67Mopar Well-Known Member

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    My 2550 serial number is in the 5K range. My friend Joe has an early model, and there's no question as to the difference in tone. Mine has a fuller, more robust sound. My effects loop sounds completely neutral. His sounds like there's a bass cut when using the effects loop. I don't know if he ever updated the amp. Could be tubes, I don't know?
     
  4. jupiter89

    jupiter89 Active Member

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  5. David Rivers

    David Rivers New Member

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    hey....I can't help but mine seems to fade in and out as well
     
  6. Kinkless Tetrode

    Kinkless Tetrode Well-Known Member

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    I had to replace the switching input jack on mine. It was causing a hum. Just mechanical wear and tear over many years. Remake the solders connecting this jack to the board if your having problems first, though. If you need to fiddle with it then its not got a good solder connection somewhere, even if they look fine. A tiny crack could happen if the jack has had a cord jerked out of it or something. Be careful, the green boards on JCM800 era amps are a bit flimsy. That is one of the nice improvements of the heavy duty double sided black colored boards on the reissues.

    If any of the switching cliff jacks are dirty or oxidized it could be a poor connection or a short circuit of some of the signal to ground through the dirt. Clean all the jacks, including the DI.

    Other components that have needed replacement on mine:

    The channel switching relay.

    The impedance selector. Check this if the output is really low or inconsistent. A short here could destroy the OPT as well. Modern Marshalls don't use this potentially problematic style switch anymore. I think there's a reason.

    The pentode/triode switch. Switch it only on standby. But wiggle the switch with your finger if you notice an usual hum or low output and see if it changes anything.
     
  7. mickeydg5

    mickeydg5 Well-Known Member

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    His post is kin to mine. What were these earlier revisions and how did the earlier schematics reflect them?

    It would be nice if these professionals learned how to note descriptions of each revision in the revision/issue release charts on the schematics. They do in other industries.
     
  8. RickyLee

    RickyLee Well-Known Member VIP Member

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    My buddy has a Silver 2550 that has a serial in the 200's. Very early indeed as I think the run started with the serial of 200.

    His amp is quite different sounding than all my later Jubes for sure. But when we finally lined his 2550 up with my black '89 2550, we found that all we had to do to get them them to sound more identical was to turn his Bass pot to 10, while mine was about 5. This alone made his Jube go from sterile and ice picky top much darker and fuller. If I then turned my Bass pot to 10, it sounded very bad and tubby for sure.

    Can you recall which components in the switching scheme that you refer to above?



    I remember reading about this many many years ago. I thought I saved a copy of the pre 3100 schematic, but at this point I have not located it. It might be on an old computer/hard drive.
     
  9. RickyLee

    RickyLee Well-Known Member VIP Member

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    I forgot to mention, that I do remember seeing the component callout numbers on the pre 3100 and post 3100 schematics having a difference of 1 somewhere down the line. As in, R29 on pre 3100 was R30 on the post 3100. This is just an example I just rolled off the top of my head, so don't take that R29/R30 example as fact as I can not recall where the alignment changed, and I did not notice an added component on post 3100 to change the order.

    Now back then, I was not very knowledgeable on electronics and such. So I am very curious to look into this now, as I have learned quite a bit these last few years. And I have a hand wired 2555 Jubilee Clone that I am considering modifying for more isolation between channels and possibly adding a dedicated Gain pot for the Rhythm channel/adding in an additional relay coil.

    EDIT/ADD: I should let it be known that I have been spotted mis-matching my amp loads both up and down. Just thought I should put that out there since I was late to that closed party . . . .
     
    Last edited: Aug 16, 2019
  10. Kelia

    Kelia Well-Known Member

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    Back in 87 when they came out , I bought two half stacks , a 50 and a 100 watts and never liked them !.....They sounded shrill so I sold them and never quite understood why people liked them ,..but a few weeks ago I got a 2555SL and I just can't stop playing!!.......awesome woody tone almost like Page at MSG !

    I can tell it's not the same amp I'm playing today !
    Very touch sensitive just with the guitar volume and very quiet !
    It also has a KT66 breakup quality but with big fat bottom end !

    Love this amp !
     
  11. RickyLee

    RickyLee Well-Known Member VIP Member

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    Yeah, maybe you had the early different circuit back in '87.
     
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  12. Kelia

    Kelia Well-Known Member

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    Didn't know until I've read you guys exchanging about it !:D
     
  13. Kelia

    Kelia Well-Known Member

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    Try Imgur for pictures!
    Very easy and works like a charm!
     
  14. mickeydg5

    mickeydg5 Well-Known Member

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    I had to go dig up some notes. I have not worked on a Jubilee for some time so memory is foggy on everything.
    The notes are from an early one, not as early as 200's but under 1000. The thing is we do not have schematics for these early amplifiers. You guys are talking about schematics but they are all generally from the same time period in manufacture. Yes there are the pre-3100 schematics as well as the 3100-up schematics (with some component numbering off by one). By the way all of these can be found on the internet. HOWEVER, there are no schematics before these to be found. The key thing about the schematics that can be found is that they all call out the "D" version board. So where are the A, B and C board schematics and revisions?

    Now the amplifier I spoke of above was a "C" board. What is the board used in your buddy's amplifier? This matters and who knows the differences from one board to another without being able to compare.

    Now to start off with the amplifier I fixed was previously modified by someone and it was obvious that they were not thorough or had a good grasp on the whole electronics picture. There were some pretty bonehead modifications. This amplifier too was more top frequency heavy lacking in low end but also had swithing issues including backwards switching operation and LED lit in RHYTHM. First off was I really did not notice component changes but rather a couple of additions along with jumper wires. The first thing I did was start comparing the "C" board to the newer "D" board schematics. There were quite a few differences including added components and board traces. Here are somewhat important things I noted.

    1) The routing/traces for the RHYTHM CLIP circuit were different. R10 100k was nonexistant and the routing to the clipping diodes came from R8 10k.
    The RHYTHM clipping circuit was setup different because the bottom trace to ground was not there and in its place was the switch itself.
    The fact that this routing was used and R10 100k was not in circuit is a cause for drop in overall volume especially in lower frequencies of the LEAD channel while increasing volume of RHYTHM channel especially without CLIP engaged.

    2) The channel switching relay/traces were actually setup backwards which meant he LED lit on RHYTHM channel.
    For some reason I do remember ajoining traces in this area that I believe could have also affected signal but did not note anything on that. I just truncated what was required and added appropriate jumpers.

    3) The effects loop had a weird bypass circuit. There was no normal routing as from SEND to RETURN via jack shunt contacts and board trace. There was a 220k from C24 .1uF to R36 1M and from that point a 1M to intersection of C27 .1uF and first LOG half of BASS VR6. R33 was also 22k instead of 10k.

    4) R11 47k between VR2 and V2a grid was a 100k instead. This too can affect volume and voicing with the above described attached RHYTHM CLIP circuit.

    5) As for bias I have noticed both 68k and 56k used at R23. I like 56k for a hotter range.
     
    Last edited: Aug 17, 2019
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  15. RickyLee

    RickyLee Well-Known Member VIP Member

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    Great info Mickey.

    My buddies board should be an A revision if you consider his serial number is within the first 75 made. But . . . . that serial number could actually not mean much if they were assembling these things similar to what Fender used to do; as in, grabbing a huge pile of parts and throwing them together with no method to keeping chassis, transformers and pcb dates close to each other.

    I will see if I can get some info from my buddy. He is always in need of money but he does not want to sell that amp to me. He only paid $250 for it from a pawn shop find maybe just over 10 years ago. The condition is not great, but it is a piece of history to me. Getting some info from him might be like pulling teeth.

    Another big thing with his amp is his Rhythm channel has extreme more volume output than the Lead channel. I remember that one distinctly. I am not sure about his fx loop and then all the switch functions in relation to the LED's either. I thought I remember seeing the red LED on with the Lead channel.

    Is the revision sticker visible on the top of the PCB looking into the amp?
     
    Last edited: Aug 17, 2019
  16. mickeydg5

    mickeydg5 Well-Known Member

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    I revised this sentence for more detailed explanation.

    "The fact that this routing was used and R10 100k was not in circuit is a cause for drop in overall volume especially in lower frequencies of the LEAD channel while increasing volume of RHYTHM channel especially without CLIP engaged."

    I believe the board number can be seen on top. There may be a sticker there. It could be under the sticker if remembering the boards correctly.
    It is either JM112A, B, C, D or something noted on the board.
     
  17. RickyLee

    RickyLee Well-Known Member VIP Member

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    OK. I got a few tidbits of info from my buddies early 2550 Jube. He was not able to look inside at PCB at this time. But I got the inspection sticker date and all transformer numbers and date codes.

    His Inspection sticker has 3-2-87, so I figure FEB 3 1987 there.

    Power xfmr Drake 1202-324/6 12 86

    Output xfmr Drake 784-139/5 10 85

    Choke 1471-263/7 1 87

    Very interesting here is that very early date code on the output transformer of OCT 1985. But could be like I mentioned earlier, just grabbing parts out of huge bins during assembly.

    He says he remembers there possibly being an issue with the channel switching LED being backwards in relation to plugging in a foot switch, but he thinks he might have disconnected the LED in the footswitch.

    Main thing is his Jube always lacked bottom end. He plugged into a small head Silver Jubilee at Guitar Center a few years after buying his pawn shop Jube for $250 (price corrected from bad memory). And he says that small head Jube he played had a much warmer sound than his. They were asking $1300. He came back a short time later to try and buy it and it was already gone and sold. He does not know/did not know to check the serial number info on that small box Jube he auditioned. Would be good info if we knew that of course.

    I am thinking about offering him a trade form my 2nd clean stock '88 2205 straight trade for his beat up Jube. He might not do it though . . . .
     
    Last edited: Aug 17, 2019
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  18. mickeydg5

    mickeydg5 Well-Known Member

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    Those transformers were not just in Jubilee but in most or all 50W of that period.

    It would be good to know his board number. Twist his arm. :)
     
    Last edited: Aug 17, 2019
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  19. microhead

    microhead Active Member

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    Wow, lol

    Just posted my Jub micros in the classifieds.... Guess they COULD be '88?

    Editing that now, haha....

    BTW s/n's
    W07216
    V25037
     
  20. mickeydg5

    mickeydg5 Well-Known Member

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    Are you speaking of micro stack solid state amplifier or the 50W with 2x12 mini stack?
    This thread is about big boy amplifiers. Just kidding. :)
    Those 3100 reference serial numbers are for tube/valve amplifiers.

    Man, the 50W double 2x12 mini stacks are nice.
     
    Last edited: Aug 17, 2019

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