Lead & Bass 50 (2100) power transformer? Swap it?

Discussion in 'The Workbench' started by Sonhenry, Nov 15, 2020.

  1. Sonhenry

    Sonhenry Member

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    hey y’all

    I’ve got an ‘76 lead & bass 50, that U.K. mail order model #2100. It’s a great amp and i gigged it really hard when I was in the U.K. I brought it back to the US and thought I’d just run it off a step up transformer, no prob. To be fair the amp is happy, but I’m tired of the extra transformer to lug around. I looked at the schematics I can find, but don’t see that there is an extra tap on the pt to switch to 120v, am I missing something? Should I just have a pro replace the pt with a US-equivalent and be done with it?

    Like I said, it’s an odd amp and I hate to mess with an old survivor, but then again, it’s my gigging amp...
     
  2. thetragichero

    thetragichero Well-Known Member

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    of course no schematics with voltages to be found but it's basically a jmp 1986 and 1987 preamp with a 50w power amp, yes?
    the 1964 (head version) schematic shows ot primaries for 110, 120, 200, 220, 240v on a rotary switch but yours doesn't have that?
    in that case whatever your preferred 50w jmp power transformer it's should be fine
     
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  3. Sonhenry

    Sonhenry Member

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    Thanks! That’s right, no rotary...

    Good to know it’s possible!
     
    Last edited: Nov 15, 2020
  4. thetragichero

    thetragichero Well-Known Member

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    i would wait for others who have more experience to confirm but that's what my googling turned up. sounds like these are uber rare - neat!
     
  5. Travis398

    Travis398 Well-Known Member

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    A picture of the inside would be enough for someone to tell if the tap was there or not.

    If not, I would change the Transformer to avoid the hassle. You already know about the hassle.
     
  6. Marshallhead

    Marshallhead Well-Known Member

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    The amp will have the usual multi primary mains transformer, but instead of the plug in selector, there should be a set of connections spread out on tag board inside the chassis, and currently the incoming wire from the mains cable will be connected to the 240v tap.

    You just need to identify the correct alternative tap for your location, and move the incoming wire, then assuming you’re going to like 110-120v, fit a stronger mains fuse - try a 3.15a first of all, might need a 4a.
     
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  7. neikeel

    neikeel Well-Known Member

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    What Marshallhead said!:agreed:
     
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  8. Sonhenry

    Sonhenry Member

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    Great thought. Here's a shot of where it looks like the wires off the transformer are connected to the main circuit board. There's others connected to the heaters, switch, etc, but this looks like several options and a jumper to what might be the UK/240 tap?

    marshall small.JPG

    Thanks all, this is really helpful and much appreciated!
     
  9. neikeel

    neikeel Well-Known Member

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    Move the link to the brown wire lug and you are sorted!
     
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  10. Sonhenry

    Sonhenry Member

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    From yellow to brown? That the right end to move?

    Thanks!
     
    Last edited: Nov 16, 2020
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  11. Travis398

    Travis398 Well-Known Member

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    If anyone knew the color code it would be neikeel, It looks like you have 5 taps to choose from assuming they are in order I would guess

    5- yellow 240 volt (245?) current connection
    4- Orange 220 volt
    3- Red 200 volt
    2- Brown 120 volt
    1- Black 110 volt
     
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  12. neikeel

    neikeel Well-Known Member

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    Black is 100
    Brown 120
    Red 220
    Orange 230
    Yellow 240
     
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  13. Sonhenry

    Sonhenry Member

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    Thanks again, y'all! All converted today, sounds great. Now that I've got it all apart its time to clean the pots, new tubes and a quick rebias and we're in gear. Oh, my lord, no 20 lb step up transformer to drag around any more.....
     
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