Note
QST, Jun 1960 p. 123.
The Electrotone M-100 is a compact, self-contained audio system designed to serve as a series gate modulator for transmitters or linear amplifiers using screen grid tubes (tetrodes or pentodes) with screen voltages of 400V or less.
The unit is versatile, proving useful as part of a main rig, in portable/mobile setups, or as a modulation source for homebrew and test equipment.
By adjusting the carrier level control, the DC screen voltage applied to the transmitter's final amplifier is controlled. When audio is introduced, it modulates this screen voltage. As audio input increases, grid current builds up a negative bias on the coupling capacitor. This automatically raises the mean screen potential of the final, keeping modulation at roughly 95% without over-modulating. Positive peaks are limited when the control tube is driven to cutoff. Negative peaks are prevented from over-modulating because the screen voltage can never drop below the level preselected by the carrier control.
Audio Capabilities: Input for crystal or dynamic microphones with a bandpass of 300 to 4,000 cycles. It features a sharper cutoff on the low end to prevent 60-cycle hum.
Built-in Tone Generator: Includes a 1,000-cycle audio generator for tuning, MCW capabilities on UHF, or double-sideband adjustments.
Over-Modulation Prevention: Automatically prevents both positive and negative peak over-modulation through its unique gate circuit.
Power Requirements: 115/230 VAC, 50/60 Hz, 30 watts.
