Product Details:

Scientific Radio Systems SR-370 solid state PA board and heatsink. A matched pair of SD1285 transistors in push-pull drive, 2 pair or MRF458 transistors in push-pull to conservatively produce 140 watts output from as little as 1/2 watt drive. Unit is broadbanded and covers from 1.69 to 30 MHz. External bandpass filters are highly recommended. Requires 13.6 vdc at 25 amps for full output.

On board thermal sensors on the output transistors provide input to an external bias control circuit to reduce output power due to high temp and control an external fan on the heatsink (not included).

Heatsink is 9-1/8" x 4" x 1-5/16" - PC board adds 7/8" to thickness. Manual included. Includes filter. Transistors alone are over $200.

Scientific Radio Systems band pass filter board for RF amplifier (left). This circuit board contains 6 bandpass filters to reduce harmonic output. Each filter is relay switched by grounding the appropriate line.

This board also includes RF output voltage and current sensing to detect SWR variations. As the output SWR diverges from 50 ohms, it is evidenced by output voltage and / or current changes. As a result, the bias on the final transistors is adjusted to reduce power output. Similarly, the output transistor case temperature monitored on the PA board is also used to control an external cooling fan and adjust the bias as needed. Supply voltage changes are also an input to this bias control circuit to reduce power output as supply voltage drops so that the output stage remains linear.

There are also 5v and 8v regulators on this board for various uses in the original radio. Manual included. Circuit board measures 12" x 7" x 1-3/4".