Stephen Cowell wrote:
Jim, I've never found a friction brake in a Leslie... my direct experience is limited to the Fender Vibratone, 21H, and 720 models... the acceleration difference seemed to be caused by the way the slow motor works, since it engages a rubber-edged wheel on the fast motor it takes over quickly, but when it drops out the lower torque fast motor has to ramp up as best it can. The 21H has an electric brake with only one speed (fast) or off. The tension on the cloth-covered rubber drive belt can set some of the accel-decel as well.
What is being called a "friction brake" is the rubber "tire" that is connected to the shaft of the fast motor. It is not so much a "brake" as it is a "drive wheel" to turn the rotor in chorale mode which is connected to the shaft of the fast motor assembly. This is a fibre wheel with a replaceable rubber tire, like a giant "O" ring, so that the spindle of the slow motor can come down or come up depending on which rotor, top or bottom on a two rotor model is referred to, engaging the slow motor while the fast motor shuts off. It's actually two motors stacked on top of the other. For those in 220 volt areas you will need to change the pulleys on these motors to compensate for 50hz as they are set of 60hz.
The Fender Vibratone. Leslie 16, 18, have the same dual stack motor, fast and slow, with the same rubber tire to achieve fast (tremolo) or slow (chorale).
On the Vibratone et al, you can switch the motors off for the single foam rotor to come to a stop.
The pulley is where the belt attaches with grooves for different speeds but only for the top treble rotor. The bottom rotor motor set has only a one speed pulley. The Vibratone and it's brethren only have the single groove rotor pulley. The picture of a top rotor motor is courtesy of Rick at Tonewheel General Hospital.
You can see the slow motor spindle as it rubs up against the rubber tire. When the Leslie is switched to fast, the slow motor turns off and the spindle retracts with special weighted springs for the up retract or the down retract of the spindle's action.
These motor stacks need alignment adjustments to get the slow motor spindle to touch the tire and be able to retract at the proper angle and degree. But if the parts are in good condition, the adjustments will hold for years depending on how much of a speed switcher you are.
This is what the pulley looks like peeking out of a Vibratone single foam rotor. Note the wingnut for adjusting belt tension on the rotor. It just moves the whole motor assembly a few millimeters:
The 720 is odd in that it has two slow motors and only one fast.
The 21 H has only one speed which is fast, there is no slow motor as that was designed to be tremolo only, or just stopped (brake). Jazz artists are known to prefer the stopped setting.
What is referred to an "electric brake" is merely an off switch within the circuit coming off the Leslie amp within the speaker which controls the switching of the motors through switches located at the organ for which it was designed, and the multi-pin Leslie cable which go anywhere from 5,6,9 pins to the now modern 11 pin.
A Fender Vibratone or Leslie 16, 18, has no amp and is a speaker only, needing an external amp. The rotor speed switching is controlled by dedicated cables and power switches.
The motors within a Leslie are 117 volts AC hence caution is needed when dealing with these voltages specially if they are directed to a foot pedal and you are handling other instruments plugged into AC.
There are modern low voltage switching circuits available that use relays to keep 117 volts out of the foot switch if you are a DIY guy/gal doing the Vibratone clone, a single foam rotor salvaged from a spinet organ or you have a Vibratone, Leslie 16, 18, missing the power and switch cables.
This photo is courtesy of Marc from Fishsticks.
For the DIY, you will want your donor rotor to look like this complete with the motors and make sure you get the ones with 2 speeds. These donors come with an 8" speaker but you can also swap them out for a 10" JBL or other brand suitable for heavy guitar tones. Check that the rotor is not spinning too much out of round and if the rotor is not damaged. You will see some rotor bumps and dents as normal specially if some gold finder dug one out of an organ for resale on eBay. The foam model is "the" tone for Vibratone vs the all wood rotors.
The electrical codes in the days these Leslie units were made were not as refined as they are today. Hammond tried his best to keep Leslies, then a separate company, from being attached to his consoles, and re-engineered his keyboards to make it difficult for Leslie connections, banning them from his dealers so work-arounds were necessary and were done in the back rooms off the Hammond dealer showrooms. Later on Hammond and Leslie were bought by Suzuki of Japan.
Although it is against the electrical code for audio and AC to go through the same cable as in the Leslie cable, this out of code issue was grandfathered in within the modern code. And you can't run these cables through a wall or through a floor as it is against code.
Depending on which Leslie model used, the internal amp has a brake circuit to where an extra wire with a switch is run from the player's position (usually at the organ rail) to shut the motors off to create the stopped effect. Modern switching relays are now made by Trek which can handle the chorale-tremulant-stopped effect with one Leslie cable instead of the previous cable and extra brake wire which were both connected to a three position switch at the rail, while most switching is only two position for those that don't want the stopped feature. Hence there are two versions of the Leslie switch. A two position and a three position switch.
These switches are for organ use.
With the specific Trek relay for Leslie amplifiers, you can have all 3 motor positions including "coast" which bypasses the Leslie's normal feature from going to chorale first before coming to a stop. By flicking the switch to the chorale position for a split second and then going to the "stop" position on the Leslie switch, you can create the "coast" feature which allows the rotors to spin down naturally by gravity.
This model relay is made for a retrofit inside a Leslie amplifier replacing the stock mechanical relay and must be done by a qualified tech.
Courtesy of Michael at Trek ii:
There are parts available for Leslies through many sources and for the more popular models.
Keep in mind the older Leslie units from the 60's and 70's are the most desired.