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Thread: Baldwin Leslie BL-1 leaking current

  1. #1
    ppp Pianississmo Aback22's Avatar
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    Baldwin Leslie BL-1 leaking current

    Hello all, I'm new to the forum. Thanks in advance. I have a Baldwin Leslie (which is less common) and play guitar through it with a custom box from "Dr. Fishsticks" to supply power to the 6 pin plug, provide a 1/4" input for the instrument, and a TRS cable plug-in for the footswitch for the single motor. With a separate preamp I've enjoyed playing the guitar through it. The problem I discovered is that when my wife came to say hi while I was playing when she touched me she got shocked! Later I got shocked when I wasn't wearing shoes. Any idea where the current leakage could be coming from? Also I have not been able to find a schematic for this Leslie anywhere on the internet. That would be helpful to know exactly which components might need to be replaced. Thanks for the help.

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    fff Fortississimo David Anderson's Avatar
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    I was given one of these to save it from going into the trash, but I haven't done much with it. I presume Dr. Fishsticks makes an interface specifically for this model since the pinout is completely different from the usual Hammond/Leslie standards.

    I will attach the only schematic I have. When it comes to shocks, there are generally two sources to look for. The first is a "death cap" from the 120VAC input to chassis ground. These were intended to shunt any radio signals picked up by the chassis to AC neutral, but, depending on plug orientation, you may end up with them connecting hot to ground. These days, we typically remove them. The schematic I have doesn't show one in the BL-1, but they were sometimes added as running changes.

    The second, less common, source of shocks is AC leakage from the power transformer. There is a procedure in the Hammond Service Manual to check for this problem, and if it is present, it means the PT may be bad. This is what three-wire grounding is meant to protect people from, but, if you just add a chassis earth-ground to a situation with a bad PT, that means that even though you are protected, you now have constant current flow to earth ground somewhere in the power transformer. This can cause it to burn up or blow fuses. (Not an uncommon situation in some old Ampegs; a tech adds a 3-wire power cord, and it starts blowing fuses.)

    The ideal solution, if you have a bad PT, is to replace it or have it rewound. Not what you want to hear, but the best solution.

    Is nothing you are using three-wire grounded? Not even the preamp? That's a little scary for guitar.

    Baldwin BL1.jpg
    I'm David. 'Dave' is someone else's name.

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    ppp Pianississmo Aback22's Avatar
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    Wow thanks David, this is all helpful. Let me say that I'm a long time musician but very new to tinkering with electrical and amps, etc. So forgive and please correct anything I have wrong. Yes the Dr. Fishsticks box was custom made for this Leslie. I actually have pulled apart the 6 pin plug and cord and figured out where the audio signal (2 leads) was going and separated that from the power signal (two leads). I'm not using the fifth pin to power the motor because the box has a separate plug for that. I successfully played the guitar through the amp by having the wires from the box soldered directly to the correct leads inside the amp, which was exciting for me. However, the shocking issue was still present. And no, neither the Leslie nor my preamp have a three prong plug with the ground. I also found this strange, as any other amp I play has a three prong plug. I was showing this to an electrical engineer friend of mine, and we were hoping to wire in a ground and have a three prong plug power source. Sounds like I would still have troubles if something is wrong with the power transformer. How would I replace that? Sorry for rambling, just processing out loud here. Thanks, Aaron

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    fff Fortississimo David Anderson's Avatar
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    There are too many unknowns here at the moment. We've got an obscure amp, a custom interface, and a preamp you haven't described. Is the preamp solid-state, powered by a wall-wart? I would get the whole system looked at by someone who's familiar with vintage vacuum tube gear. Your EE friend may very well know what's doing in this context, but some do not, the reason being that Electrical Engineering is such a huge field. That's no criticism of your friend's knowledge. None of this stuff has been taught in EE programs for decades. I know about it because my grandfather was an EE born in 1902.

    The first step is to figure out where the problem is. In guitar amps, most of the time, it's a "death cap." Has that BL-1 amp been recapped or serviced at all?

    And, yes, to confirm, you can't just wallpaper over a leaky transformer with an earth-grounded power cord.

    You probably won't find a drop-in replacement for that PT unless you were to have it rewound. Otherwise, you'd have to find a generic transformer with the correct ratings, which wouldn't be too hard since the circuit is simple and the current demands not that high. The original PT also has the 12V winding for motor switching, but it sounds like you're not using it. There are a number of sources for tube amp transformers: Hammond Mfg., Edcor, etc... Even a Fender Deluxe Reverb PT might work. Minor mods might be necessary.
    I'm David. 'Dave' is someone else's name.

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    ppp Pianississmo Aback22's Avatar
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    The preamp I'm using is a Presonus tube preamp with a 12ax7 in it. It is not a grounded power supply. But the preamp is somewhat irrelevant because I also used a simple guitar boost pedal which was 9vdc powered (again, no ground) and that functioned fine. With either one I have experienced the shocking. I've had the BL-1 amp & cabinet for 15 years but never used it or opened it up until a year ago. I found the Dr. Fishticks box online, with a female 6 prong plug so I could power the BL-1. It sounds great! Anyway I got the amp from an elderly couple and they only used it with an accompanying organ. I'm not aware of any tech work being done to it and I don't spot any "death cap" or parts that appear to be different than original.

    So I'm thinking it is the power transformer. You said a Hammond manual gives instruction to test this? It seems that this would be a first step in order to move forward. Thanks. I'll include picture(s) of the inside of the amp.20171209_020411.jpg

  6. #6
    fff Fortississimo David Anderson's Avatar
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    Here's the relevant leakage test:

    Leakage Test.jpg

    In practice, I don't know that the 0.01uF cap is entirely necessary unless you're very close to a radio transmitter.

    I would consider replacing all those "bumblebee" capacitors. They may not be the source of this problem, but they do fail. Some people with "questionable judgment" will buy them from you on eBay.
    I'm David. 'Dave' is someone else's name.

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    ppp Pianississmo Aback22's Avatar
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    Great, I'll get my engineer friend to help me run this test. And a question- the isolation transformer (inside the chassis on the far side) should be alright? Also which exactly is the .01uf cap? I'll look into replacing those other capacitors too. I already had that long one with blue and green blow up on me. It's fried. Hopefully can find the right replacement.

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    20181015_205252.jpg Here's what the inside of the power transformer looks like.

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