Craig Brougher wrote to me:
> By the way, the Ampico B lever overheating can also be caused by an
> open resistor across the points. That forces the points and the motor
> to also overheat, working too hard and fast without damping. The
> resistor doesn't get nearly as hot as the points will if left to run
> undamped, and it fries the motor armature pretty quickly.
I hadn't thought of this possibility, as power resistors seem quite
reliable, but Craig has previously mentioned that the connections can
loosen and fail. So I located the "Ampico 1929 Service Manual" and
read it thoroughly.
The external adjustable resistance unit is fastened to the rim of the
piano, in-line between the power cord connector and the pump motor,
and protected by a perforated-metal cover. (It can get very hot --
caution!) The governor resistor is mounted inside the base of the
note sheet motor and governor assembly.
For 110-120 vac 60 Hz mains the resistance of the external adjustable
resistance unit is set to 25 ohms, and the governor resistor is 360
ohms (350 ohms is a satisfactory substitute).
The service manual says about the external resistor, "If the drawer
motor is not strong enough for the heaviest loads, there is too much
resistance. If it will not govern and runs too fast at the lightest
loads, there is too much resistance in the circuit."
The main function of the governor resistor (connected in parallel
with the points) is a spark suppresser. The lower the resistance,
the better, because less voltage can be developed when the points
open. I assume that Dr. Hickman experimentally found the lowest
resistance which could be used without the motor crawling when the
points are held open at Tempo "0".
If the Ampico B is to be operated by electric valves, such as the
PowerRoll unit, a micro-switch could be installed to shut off the
motor completely when the Tempo lever is at "0". Connect a metal-
oxide-varistor (MOV) spike suppresser across the micro-switch (and
another across the points) to protect the contacts.
Elsewhere in the discussion about the motor, the writer (Dr. Clarence
"Slight heating of the tempo lever after the Ampico
has been played for some time does no harm."
BUT, Craig notes that excessive heating of the Tempo lever is an
indication that the governor resistor has failed, and so the points
can really throw sparks and get quite hot.
Regarding lubricating the motor and shafts, Hickman also says,
"** Use Singer sewing machine oil. **"
Seventy years later it's still good advice!