I bought this Hammond M3 with a Leslie 145 cabinet from a friend who was moving and needed to clear out his recording studio. They were both in rough shape, but they were cheap. Both are legends, the M3 is a "baby" B3 (the most famous of the organs) that features on recordings such as "Green Onions", and the Leslie cabinet has been used by organists as well as guitarists for decades who wanted it's swirling sound.
The electro-mechanical Hammond Organ is one of the only uniquely American instruments there is. Hammond started out building clocks, and he used some of that experience in designing the organ. It never needs tuning because it has a synchronous motor that uses the 60Hz line frequency of US utility power to ensure it runs at the right speed to keep the organ at pitch.
The organ mostly worked, but was pretty tired. Percussion didn't work, nor did the fabled mechanical & electric chorus/vibrato.
The Leslie was far worse off; no amplifier, no crossover and the wrong bass driver altogether. There was also no interface for the Organ to control the Leslie. I had never owned or worked with a Hammond or Leslie cabinet. It was all new.
We had our work cut out for us.
The keyboards ("manuals") were in solid shape.
Since it had no amp or crossover, or even the proper interface I rigged up an old stereo to get the Leslie to make sound. This is how everything arrived. Lots of potential, but not much else.
The inside of a Hammond, up top that row of capacitors is the vibrato array, the big mechanical thing in the middle is the tone wheel generator - the thing than creates the tones that get added together to make the organ. At the far left in the middle is the vibrato scanner. Down on the lower shelf is the amp. They are pretty intimidating.
The used 147 amp I found on eBay is what would have come in the Leslie 145. Leslie cabinets were made by a different company (Hammond actually did not like them) and how they integrated in this case was by taking the speaker out from the organ (which had its own speaker) and running it into a resistive load that had a rheostat (the "volume" control here) to adjust organ volume vs Leslie volume. Then I needed to find the adapter box and the special cable to connect up the organ. The Leslie gets both AC power and the organ signal over an umbilical cable. The more famous B3 + Leslie 122 combo connects using a balanced line level cable. It's a different interface from the Organ, and a different amp in the Leslie.
Step one was testing tubes and re-tubing the organ's amplifier. Then I got to work on the Leslie amp. It was in ok shape, but needed some TLC. Tubes, filters and odds and ends.
I think that resistor drifted high... lol
The new filter cap from CE Dist fits perfectly.
Much better.
Found a proper P15LL bass driver, big AlNiCo magnet goodness. This looks to be 17th week of 1959. Should have lots of soul by now.
Found the adapter interface and cable (brown, lower) on eBay as well. It takes in AC power, the speaker output (it replaces the onboard speaker) and the switch contacts from the half-moon Leslie switch on the organ. Ugly but effective wiring here.
I ran new AC cords to the motors for the fast and slow speeds (fast in brown, slow in white)
installed a new cross over so we could use the spinning horn again.
I replaced the old drive belts. This is looking up at the belt that drives the low frequency drum. The trick is to not make it tight - it needs to slip to come up to speed quickly. If you do it right it should take around 10 seconds.
I also replaced the upper belt for the high frequency horn. One side is open, one side is blocked by design. The doppler effect you get from it spinning is a big part of the vibe.
next I re-furbished the electric motors.
There is a kit of soft parts to replace
You separate the fast & slow motors to work on them.
While they are apart you can inspect the mechanical bits and make sure everything is ok.
The Hammond is a little tricky in that the amp doesn't come out easily. Normally you would want to troubleshoot it while it's on so you can trace signals & measure voltages. Since this was a pain, and since the websites I read pointed to more common issues, I tackled them first. I traced the signal in the parts of the amp I could get to. But the problem remained.
I rebuilt the Vibrato scanner's capacitor array. The first new one in on the far left (above).
All done.
I re-capped the tonewheel generators while I was there.
A bunch of wires to disconnect, plus the oiling thread, plus the mechanical connections make the vibrato scanner a challenge to work on. One common issue seems to be they grow metallic whiskers inside that short the scanner. That was not what happened here, but something to keep in mind.
The Vibrato scanner after removal. This is a rotating capacitor (that is the motor on the right side above). You have to be careful of the string - that is how things get oiled. The oil goes into that little tub up top and gets wicked away by the string. There is a sponge in there too (not in photo)
Checking the guts of the scanner. (they were ok, although I bought a spare on eBay just in case) This is the contact that allows the rest to spin.
Nothing else got the vibrato working so I had to pull the amp partially out. It turned out to be an open resistor in the amp stage right before the vibrato circuit, so the signal never got there. Now it works really well.
This is a block diagram of how their crazy mechanical vibrato works. Those capacitors add delay. The mild & stronger settings just use more of the caps in the delay line.
In case your organ is missing the rear cover, here are the actual oiling instructions. I wind up oiling mine about once a year because it is not getting played all the time. The oil is still sold and is basically sewing machine oil as far as I can tell. One great thing is how much support these old organs have, you can still get all kinds of parts for them. Someday I would love to have a B3, but for now this is pretty neat.
Here is a quick demo shot on my phone (1:09) with minimal talking. Just plain, with vibrato, and then with vibrato & Leslie on fast so you can hear it spin up and spin down.
Sources:
Hammond Organ https://en.wikipedia.org/wiki/Hammond_organ#
More history: https://www.soundonsound.com/people/history-hammond
Repair Info & More: https://bentonelectronics.com/the-hammond-story/
Schematics & more: http://captain-foldback.com/Hammond_sub/hammond_schematics.htm
Lots of parts here: http://www.tonewheelgeneral.com/
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