The ES4L4-B is a combination soft-start/soft-key/bias board for the L4-B amplifier. This all-in-one board limits inrush current during amplifier start-up by placing a small resistive load in series with the AC mains.
The load resistor is switched out of the circuit by a relay approximately 2.5 seconds after power-on. It also features a opto-isolated soft-key circuit that reduces the voltage on the keying line to 12 VDC at less than 10 mA current that is also interlocked with the soft-start.
The kit also utilizes a string of 10 1N5408 diodes and a 100KΩ resistor to provide DC cutoff bias and user-adjustable idle current biasing.
There is also a ready light output on the board for those who wish to use it. The unit mounts on the underside of the RF deck using existing holes in the chassis; no extra holes or modifications to the chassis are required. The board is assembled and comes with all necessary mounting hardware, miscellaneous parts and wiring. The Instruction manual is included.