These were first built in 1981 and consisted of :-
510 Preamplifier (MC add-on option)
520 Stereo Power Amplifier 2 x 40W 8R
530 Mono power amplifier 1 x 75W 8R
540 Active Crossover (Mono)
The construction was simple folded steel. Covers were painted with crackle matt black finish. The preamp was powered by two 9V (PP9) dry batteries.
The preamp PCB was the CPR1. This is upgradeable. The switches were silver plated and should be replaced with gold plated ones which I keep in stock.
Power amps usually had 35-01 issue 5 PCBs
Active crossovers were specifically tailored to certain speakers e.g. Mission 770. They were 24dB/octave Linkwitz and had muting using Jfets. Some passive networks were added for EQ.
Outline in HiFi Choice c 1980