Arange

The first 'range' of mixers were called the 'A' range. (I assumed we'd then go onto making a 'B' range, and so on. In the event, the next series of desks were called 'System 12'.)
I had toyed with the idea of a valve (tube) mixer, but I didn't like the thought of making lots of metal boxes! There was only one type of amplifier used, and each had transformer output. I am a great believer in the use of transformers: they neatly avoid ground loops, the signal can be sent over some distance - the low impedance and balanced output helping to keep out noise. However, the most significant advantage is that if you let the transformer go into distortion first in the chain, the waveform will be smoothed off, rather than a straight clip. The distortion produced in much more acceptable to the human ear.

To save money, both the mic and line amps were exactly the same. The very early printed circuit boards were cheap paxolin, with the copper 'soldered over' the copper tongues where they plugged into slots on the console.
Four silicon transistor were used (2 x BC109, 2N697 & 2N1132), along with an off board transformer. They ran off a single 12 volt supply. (Later increased to 15 volts to provide more headroom - +24dbm.)

Later, we could afford to have professionally made PCBs. They also has a Painton 15 way edge connector, which was more reliable than the plated fingers on the prototype. The design of this mic/line amp never changed.

Early mixers used Elcom, 600 ohm, constant impedance, stud faders. Sometimes we were asked to use the more expensive Painton equivalents - pictured right. Later, we moved to Penny and Giles, 10K log, carbon track faders.

If you look closely on the enlarged images, you'll see the ferrite core used in the EQ section, and the output transformer.