The amplifier is housed in two readily available aluminium boxes, mounted back-to-back. The top unit houses the actual amplifier along with the R.F. Change-Over relays and power detector circuit. The lower unit houses the six, five element Chebyshev filters along with the control circuitry on the back panel and the front panel control board. Right from the start, I had the idea of having the amplifier ‘track’ my IC725 (or any ICOM transceiver). As is clear from the photograph below, space is a premium on the ‘lower deck’, and I didn’t want to use the ‘upper deck’. Therefore it was necessary to build the ‘band switching unit’ as an external unit. This worked out quite well for a number of reasons. Initially, the DIN connector on the rear panel was for direct interfacing with ACC2 on ICOM transceivers, carrying PTT, ALC and Band Voltage.
However, for some reason that I have not been able to figure out, the PTT line on ACC2 is not the same line as present on the Phono connector, and as such is not compatible with the amplifier. Abandoning the concept of a single cable interface left me with a redundant connector. Consequently, the DIN connector now handles the Band Switching Interface. There is a switch on the rear panel of the amplifier for switching between Manual Band Switching and Automatic Mode.
Lower deck nearing completion
Right - The 300W Amplifier PEC