From joek1000@aol.com Wed Jul 13 05:57:53 2005
Subject:A little Leslie history - motors spinning in opposite directions

I recently compared my 330 whose top and bottom rotor spin in the
same direction with a 147 whose rotors spin in opposite directions. I
started thinking about replacing the upwards pointing motor in the
330 with a motor that points downward. It would involve cutting a
hole in the bottom shelf and installing the motor pointing down. I
asked Harvey Olsen about it and here is his response. BTW, Harvey is
a retired tech who was personal friends with Don Leslie.

I thought it might be interesting to some readers on the list....

Subject: Re: Leslie question

<< I have another Leslie question! I have a 330 that works fine
but I'm not crazy about how the top and bottom both spin in the same
direction. I noticed a dramatic difference in the sound compared to
the opposite rotation of the 147. >>
 
Joe:
 
For starters this is not a defect. I once asked Don Leslie about this
"problem" but he thought any discussion of rotor direction was
silly. The fact that some models have rotors that spin in the same
direction, and others where the direction is reversed was
unintentional. No one even thought about rotor direction when these
Leslies were designed.
 
The direction that a Leslie rotor spins is entirely dependant on how
the motor is mounted in the cabinet. Very early Leslies like the
original "30 series" (30A. 31A, 31W, and 31H) had their lower
motors flipped around so the drive pulley was underneath. As a
result, the rotors spun in opposite directions.
 
Then starting with the 21H in 1951, the lower motors were suspended
from the bass speaker shelf (like in your 330), so the rotors spun in
the same direction. This was true for ALL single-speed models in
standard 41" or 33" cabinets (22H, 47, 51C, etc.).
 
When two-speed Leslies were introduced in 1963 (122, 147, 251, etc.),
the lower dual motor assembly was again flipped and relocated in the
middle compartment because the new slow motor interfered with the
tube power amp. This was not the case in solid-state models like
the 330 that had plenty of room inside, or didn't have a wood cabinet
equivalent like the 760, so the rotors in these models spin the same
direction like in the earlier single speed models.
 
<< I'm thinking of buying a bottom Leslie motor for a 122 or 147. >>
 
Waste of time..this won't help a bit unless you are willing to rework
the 330's bass speaker shelf so the 122 motor assembly mounts in the
middle compartment like it does in the 122 and 147 cabinet. It's not
the motors but how they are mounted in the cabinet. Unless you are a
first class woodworker, and can do this job in such a way that it
looks like the 330 came this way from the factory, you could wind up
with a serious mess on your hands.    
 
<< Also, is the wiring different between a 122 motor and a 330 motor
so that I could just swap the motors? >>
 
No, the motors are all the same. However, if you are absolutely
determined to do this mod, call me and I will walk you through the
procedure. It basically involves reversing the direction of your
existing motors by disassembling them and flipping the motor fields.
Buying that 122 lower motor assembly would be a waste of money. 
 
Harvey Olsen