The Gates SA-38 Limiting Amplifier has been meticulously designed to meet the rigorous demands of modern broadcasting stations, whether operating in AM, FM, or TV. It is an exceptionally low distortion, low noise, and fast-acting limiter, entirely free of thumps or chirps, even during attack times.
The limiting action is achieved by routing a portion of the output voltage through a full-wave rectifier and applying a negative DC voltage to the second control grid of the push-pull 1612 first-stage amplifier tubes.
As the output voltage rises on the Gates SA-38, the grid becomes increasingly negative, reducing the flow of current and consequently lowering the gain of the first stage. This design ensures that high levels of compression can be achieved without introducing significant distortion, as evidenced by the rated maximum distortion of 1½% at up to 20 decibels of compression.
The amplifier employs three fully push-pull stages, which are powered by an accurately engineered and regulated power supply. The attack time of the Gates SA-38 Limiter is effectively instantaneous, and six different release times, ranging from 0.2 to 1.2 seconds, can be selected via a switch on the chassis.
A large 4-inch dual-scale meter is provided, allowing users to read the level of limitation directly in decibels of compression. Additionally, a switch on the front panel enables the meter to display a second scale reading directly in VU.
The amplifier includes a T-network range control with two-decibel increments, adjustable from +4 to +42 VU. This control can be connected either across the output of the limiting amplifier or to an external circuit for other measurement purposes.
Ladder-type attenuators are included in both the input and output circuits of the Gates SA-38, enhancing its versatility. The meter is a 4-inch illuminated unit, designed for clarity and ease of use.
The exclusive Gates SA housing ensures straightforward front-of-cabinet servicing, making maintenance simple and efficient. Jacks are included for measuring the cathode current of each tube, further enhancing its functionality and accessibility for technical adjustments.
