PA3DUV ICOM 2KL Modification

The ICOM 2KL solid state HF amplifier is equipped with open frame relais for RF input and output switching. For most modern HF transceivers the open frame relais are too slow and result in hot switching. This was the case with my amplifier, resulting in contact failure of the relais. Richard Measures AG6K provides a simple and reliable solution to solve the problem of hot switching amplifiers. Check out his website!  Since I wanted to use the 2KL for HF pactor as well I decided to puchase the QSK kit and change the T/R changeover circuit in the 2KL. The stock input relay on the main unit board was replaced by the High Speed Matsushita RF reed-relay, 1mS, SPDT, Rh-Au contacts, RSD-12V, shielded, 150W at 50-ohms. This relay is in the QSK parts kit sold by Richard Measures. His secretary will send you the kit with printed circuit diagrams on nice colourful paper. The Matsushita RF reed-relay was glued on the main unit PCB with a dab of silicone compound. The relay could be mounted at the stock relay position on the Main Unit board, see picture.

The output relay was a different story. The stock output relay of the 2KL is mounted inside the Filter Unit. The Kilovac HC1 was purchased from Allen Bond, President of Max-Gain Systems Inc.  It did not fit into the narrow gap between the wall of the Filter Unit and the row of band relays. Way to go is to put that relay outside of the filter unit. The output relay is mounted on a small aluminium bracket, suspended by silicone rubber strips.  The 500 watt RF from the finals is fed to the relay with a short section of RG58 coax.
The output is wired straight to the output connector at the backpanel of the amplifier. Leave the connection to Filter Unit as it is, since that is needed for the SWR measurement circuit of the amplifier. The bypass coax is connected to the terminals of the relay.

For the control circuit of the output relay, a small piece of epoxy copper clad board is used, The copper surface was divided in sections with the help of a small saw.  On these sections the resistors, diode and high voltage switching transistor was placed. The small board was placed adjacent to the output relay.  The board consist of the series resistor, the parallel resistor and diode and the switching transistor. The relay is powered by the 43 V collector voltage, the series resistor (200 ohm) limits the current through the relay coil (77 mA) and the parallel resistor (510 ohm) enables fast coil flux discharge in order to minimize the T-R  cycle time. Relay and control board are bolted to the Filter Unit cover, adjacent to the Main Unit. The T13 and 43 V HV are taken from the Main Unit board.