22-01-2023, 02:09 PM
(This post was last modified: 22-01-2023, 02:14 PM by Lucien Nunes.)
Ha, a good flavour of the trials of gigging an organ. I don't really collect Hammonds and stage / combo organs so I don't see the worst of the damage that results. I have one Compton retrieved from mainland Europe that appears to have been gigged, judging by the wear and tear. That must have taken some effort, it wasn't chopped so the whole 5cwt / 250kg console was shifted in one piece.
Re. tone generator motors. The original Hammond motor system was such a universally recognisable characteristic that it hardly needs introduction. For the non-Hammond players out there, the synchronous drive motor was not self-starting. You would flip both the start and run switches causing a self-starting induction motor to accelerate the synchronous motor, and then release the spring-loaded start switch once up to speed to allow the synchronous motor to take over.
Compton publicity also emphasized that their organs could not go out of tune because they didn't contain oscillators. The unstated corollary as with Hammond is that they need lubrication, thereby trading one kind of maintenance for another. Comptons have always been self-starting. The large models with external tone generator cabinets use induction motors where the speed mainly depends on frequency closely but is also slightly dependent on line voltage and mechanical load. However, the huge 1/6hp motor has so much torque in reserve that any theoretical speed variation from changes in voltage or oil drag is trivial in practice. Later examples have a subtlety in that although the AEI motor was designed for a single run capacitor, Compton found the optimum value for minimum vibration when running at light load lower than that specified, so they added a current-operated relay to switch out half the capacitance after starting. For the smaller models with internal tone generators they used induction-start synchronous-run salient-pole motors that pull into lock by themselves.
As for the other makers of rotary electrostatics, Dereux used an induction motor and provided a pitch trim rheostat in series. The Dereux tone generator is quite a marvel, it runs like a Swiss watch, you can make it turn just by blowing on the drive pulleys. The whole thing is built into a foam-lined box that hangs in free air inside the console on two coil springs to isolate it mechanically. More on that later. Parie used the oversized induction motor principle for their electrostatics, while their electromagntic Italian-built PARI models had a Papst external-rotor hysteresis-synchronous type. I'm not sure what motors the US-made Electro-Voice generators used.
Before leaving the subject of synchronous motors, the reason for some types not being self-starting is interesting. The hysteresis motor works by the rotating stator flux dragging zones of magnetic remanence around the rotor with it, forming a set of virtual poles that create a unidirectional torque because they are always trailing the flux vector. Provided the load torque is lower, the motor will be able to accelerate to synchronous speed, at which point the virtual rotor poles stop moving relative to the iron. The salient-pole (reluctance) motor is not inherently self-starting because the reluctance torque alternates in sign as the rotor is attracted to the flux vector via the smallest angle - half the time that's forwards and half the time backwards. This is true of the original Hammond motor, hence the separate starting motor, and also large industrial synchronous motors and AC-energised rotary converters, which have a 'pony motor' for starting.
The motors used in Comptons and late Hammonds are self-starting by virtue of an additional cage winding in the rotor to create starting torque by induction, so the motor will run up to induction speed (1425rpm) with the alternating reluctance torque superimposed at the slip frequency (around 1-1.5Hz at induction speed.) Above this speed, the induction torque drops to zero at synchronous speed (1500rpm). Therefore the accelerating impulse from 1425 to 1500rpm must be developed in one slip cycle over 180° electrical (90° mechanical) rotation while the torques align, which puts a limit on the size of flywheel that will pull in no matter how freely it runs. A larger moment of inertia will never pull in because before it reaches synchronous speed the reluctance torque changes sign and starts to decelerate it again.
Motors:
Parie / Compton external 5-inch generators / Compton internal 2.5-inch generators
Re. tone generator motors. The original Hammond motor system was such a universally recognisable characteristic that it hardly needs introduction. For the non-Hammond players out there, the synchronous drive motor was not self-starting. You would flip both the start and run switches causing a self-starting induction motor to accelerate the synchronous motor, and then release the spring-loaded start switch once up to speed to allow the synchronous motor to take over.
Compton publicity also emphasized that their organs could not go out of tune because they didn't contain oscillators. The unstated corollary as with Hammond is that they need lubrication, thereby trading one kind of maintenance for another. Comptons have always been self-starting. The large models with external tone generator cabinets use induction motors where the speed mainly depends on frequency closely but is also slightly dependent on line voltage and mechanical load. However, the huge 1/6hp motor has so much torque in reserve that any theoretical speed variation from changes in voltage or oil drag is trivial in practice. Later examples have a subtlety in that although the AEI motor was designed for a single run capacitor, Compton found the optimum value for minimum vibration when running at light load lower than that specified, so they added a current-operated relay to switch out half the capacitance after starting. For the smaller models with internal tone generators they used induction-start synchronous-run salient-pole motors that pull into lock by themselves.
As for the other makers of rotary electrostatics, Dereux used an induction motor and provided a pitch trim rheostat in series. The Dereux tone generator is quite a marvel, it runs like a Swiss watch, you can make it turn just by blowing on the drive pulleys. The whole thing is built into a foam-lined box that hangs in free air inside the console on two coil springs to isolate it mechanically. More on that later. Parie used the oversized induction motor principle for their electrostatics, while their electromagntic Italian-built PARI models had a Papst external-rotor hysteresis-synchronous type. I'm not sure what motors the US-made Electro-Voice generators used.
Before leaving the subject of synchronous motors, the reason for some types not being self-starting is interesting. The hysteresis motor works by the rotating stator flux dragging zones of magnetic remanence around the rotor with it, forming a set of virtual poles that create a unidirectional torque because they are always trailing the flux vector. Provided the load torque is lower, the motor will be able to accelerate to synchronous speed, at which point the virtual rotor poles stop moving relative to the iron. The salient-pole (reluctance) motor is not inherently self-starting because the reluctance torque alternates in sign as the rotor is attracted to the flux vector via the smallest angle - half the time that's forwards and half the time backwards. This is true of the original Hammond motor, hence the separate starting motor, and also large industrial synchronous motors and AC-energised rotary converters, which have a 'pony motor' for starting.
The motors used in Comptons and late Hammonds are self-starting by virtue of an additional cage winding in the rotor to create starting torque by induction, so the motor will run up to induction speed (1425rpm) with the alternating reluctance torque superimposed at the slip frequency (around 1-1.5Hz at induction speed.) Above this speed, the induction torque drops to zero at synchronous speed (1500rpm). Therefore the accelerating impulse from 1425 to 1500rpm must be developed in one slip cycle over 180° electrical (90° mechanical) rotation while the torques align, which puts a limit on the size of flywheel that will pull in no matter how freely it runs. A larger moment of inertia will never pull in because before it reaches synchronous speed the reluctance torque changes sign and starts to decelerate it again.
Motors:
Parie / Compton external 5-inch generators / Compton internal 2.5-inch generators
