I bought my COPICAT second hand. I then spent quite a bit of time restoring it due to its poor condition. I remember going to Watkins Electric Music in SE London and buying new heads for it and also managed to get a Mark II (?) circuit to replace the original electronics. This I recall was a printed circuit board with the valves in their sockets mounted on it.
I had previously built an echo unit from an article in the magazine Practical Electronics in 1965, but it sounded crappy! The WATKINS COPICAT was far superior.
It had two input channels with individual VOLUME controls. The other two controls I think were called SWELL and REVERB and controlled the intensity/duration of the effect. The three push buttons selected the playback heads 1, 2 and 3 or a combination of them. Selecting only head 3 produced the longest echo due to it being the furthest away from the recording head.
The spring loaded tape tension arm also carried a small magnet which erased the tape during every revolution. The head to the left is the recording head followed by the three selectable playback heads. The friction drive spindle and a tape guide are at the far right. In the cable pocket was a foot switch allowing the echo unit to be switched in or out whilst playing. It really added that 'something extra' during guitar solos, but the frequent outages due to the tape breaking was its downside. I always went to gigs with a good supply of home made tape loops! I wonder where it is now...