THE TUNING FORK REGULATOR
The Hammond Organ is furnished in several models designed to operate from a closely
regulated 25, 50 or 60 cycle current source. The tone generators are driven by
synchronous motors and any variations in frequency will vary the speed of the motors
and thus the pitch of the instrument. For example, a frequency variation in 60 cycle
current of ½ cycle is noticeable in the output of the organ, and a variation of as
much as 12 cycles is definitely objectionable.
The tuning fork regulator is a device of our manufacture which is designed to
furnish sufficient closely regulated current of proper frequency to operate the
organ from unregulated AC or converter AC as produced by a DC to AC rotary
converter.
Start motors, preamplifier and power amplifiers are not critical to slight frequency
variations, so when the frequency regulator is used it is connected to furnish
regulated current only to the synchronous run motors.
MODEL G REGULATOR
The Model G regulator is designed for AC operation only, and may be energized by any
23 to 63 cycle line. Current consumption is approximately 125 watts. This must be
taken into consideration when the organ is to be operated from the output of a DC to
AC converter. Failure to provide a converter of adequate size may result in low
line voltage and impaired operation of the instrument.
CIRCUIT
Figure 1 shows a circuit diagram of the regulator. A straight vibrating arm is used,
with push-pull pick up coils and a permanent magnet. The signal is passed through a
push-pull resistance coupled circuit consisting of two 6F5-G tubes and then into two
RK-49 output tubes.
R-42 and R-52 furnish grid bias to the tubes, while R1 provides proper screen
voltage for the output tubes. Oscillation is maintained by a driving coil fed
through a 6C5-G or a 6J5-G tube. (These tubes are interchangeable).
A small neon glow lamp across the output indicates proper operation of the
regulator. Resistor R-33 protects the neon lamp in regulators having 230 volt
output. The output switch connects a power factor correcting condenser in order to
obtain maximum output when two running motors are to be supplied. The power supply
circuit employs a full wave rectifier with a single choke filter and an oil
condenser block.
The 115 and 230 volt models differ in the power transformer and output transformer
used. Power transformers for both voltages have marked taps to compensate for slight
line voltage variation. Models for 50 and 60 cycle output differ only in the
vibrating reed.
Tubes used: 1 5Z3, 2 RK-49, 2 6F5-G, and 1 6C5-G or 6J5-G.
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