Hello,
Pictures attached...
Please can I throw into the mix the sound to light unit from the 1974 Practical Wireless. I built this one in the days of doing social club discos and playing George McCrae, Rock Your Baby and Higher Ground, Stevie Wonder and trying to impress the girls with the slick DJ stylee and failing quite miserably! From memory it used a “backwards” connected LT transformer to trigger the TRIAC.
The other is the ETI disco project from 1976 (sorry for the upside down scans). The company I was working for at the time in Southend in the mid/latter part of the 70’s made the cabinet for Maplin. We cribbed the amplifier module/circuit and we modified it to drive 2SD424’s in Quasi-Complimentary instead of the 2N3055/MJ2955 as they kept blowing.
….Good days
Terry