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Replacement relay for Leslie 120

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  • Replacement relay for Leslie 120

    The original Potter & Brumfield relay in my Leslie 120 has gone kapputt. The energiser coil seems to be open-circuit (tested with a multimeter, chassis removed from the Leslie cabinet), but mysteriously it will occasionally still work when connected to my Hammond L122. The half-moon switch and the wiring from the organ seem to be OK, and I've actually caught the relay in the act of switching all by itself while my multimeter was connected - the voltage didn't change, but the relay switched over. So I'm assuming that the relay is toast and needs to be replaced. Tempted as I am by the wonderful solid-state relay conversions out there, I'm really looking for a quick fix so that I can demo the Hammond ready for sale. The bass-only 120 isn't the finest Leslie in the world, and I assuming that a serious buyer for the organ would want to replace it with a 145 or similar anyway.

    This is a 230v/50Hz Leslie made for the UK market, and I measured the voltage across the relay coil during (attempted!) operation:

    Tremolo (=fast) / 108 Vac / Not energised
    Chorale (=slow) / 230 Vac / Energised

    So the problem is that the relay will not energise to enable slow speed, even though the half-moon switch is commanding it to. While I assume that the original Potter & Brumfiled relay is no longer in production, there are plenty of general purpose relays out there with what appears to be a good spec. For instance, Potter & Brumfield themselves have the T92S7A22-240:
    ...which looks OK except for the spec for the coil release voltage, which is stated to be 24 Vac. So there's a chance that the relay would energise OK, but would never let go when the half-moon switches to fast speed. So my questions are:

    1. Is it correct that the Hammond should be supplying 108 Vac to the relay when it's supposed to be un-energised, or might there be a fault with the Hammond?

    2. Is there a known good modern replacement relay that won't be affected by this seemingly very high "off" voltage?

    By the way, I've never had a problem with audio switching "thump" with the original relay (when it last used to work properly, prior to sitting in dry storage for about 5 years). I'm happy and competent to mount and solder in a new relay even if it's physically very different to the original - I'm very wary and careful about all the mains voltages present in both the organ and the Leslie!

    Grateful for any pointers you guys can give me, even if it's for parts available in the US only as I do cross the pond once in a while. Some photos are (hopefully) attached.
    Click image for larger version

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  • #2
    I can't say where you'll find a suitable relay in the UK, but the voltage across the relay should be zero in the "tremolo" position. Check your wiring!
    Current organs: AV, M-3, A-100
    Current Leslies: 22H, 122, 770