Oo Modulation For The Amateur Phone

The Class B Modulator, using transformer coupling to the radio-frequency amplifier, eliminates the high wattage tubes with the high plate voltages used in the Class A modulator 'system, and permits 100% modulation with relatively low power. A modulator and a speech amplifier as shown in the accompanying diagram, using only two 210-type tubes in push pull as the modulators, will easily modulate 100% some 50 watts plate input to a Class C radio-frequency amplifier.

In the diagram the microphone anil speech amplifier circuits are typical of those in use in amateur modulation



B*230v eov DC 7 3V AC B.SOOV

B*230v eov DC 7 3V AC B.SOOV




Wiring diagram for a complete speech amplifier and Class B Modulator, capable of modulating 50 watts of plate input for a Class C radio-frequency amplifier. See the Legend below.*

systems at the present time. The necessary additions are the input and output transformers of the modulator. General Radio Type 292-A and Type 292-B Transformers have been designed and built to fulfill the needs of

Left: Type 292-A Transformer Right: Type 292-B Transformer

the amateur desiring to change his modulator system to Class B.


Ri—Type 301 Potentiometer, 200 — . $1.00 R2—Type 471 Potentiometer,

R3—Type 437 Center-Tap Resistor . .50

Li—Type 379-T R-F Choke 1.25 T,—Type 585-M Transformer (for single-button microphone) . 10.00 Type 585-M2 Transformer (for double-button microphone) . . 10.00 T2—Type 541-A Transformer 7.50 Tj—Type 292-A Transformer 7.00 r\\—Type 292-B Transformer 10.00 T5—Type 565-B Full-Wave Transformer 13.50

T6—Type 545-B Transformer 10.00

rriHE GENERAL RADIO COMPANY mails the Experimenter9 without charge, * each month to engineers, scientists, and others interested in communication-frequency measurement and control problems. Please send requests for subscriptions and address-change notices to the

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