[Hartley118]

I’ve never seen this material before, despite having an interest in Decca’s early work on the recording and reproduction of their new microgroove records. In particular, the double triode (6SL7) high gain preamp is similar to the first section of the amplifier in the well-regarded Deccalian record player where it’s followed by a 6V6 output stage.

It reads like a development report on early Decca amplifier design, which I believe was led by Harvey Schwartz who came along with Decca’s acquisition of Brunswick in the USA. What it doesn’t mention is their neat principle of achieving the 78/LP equalisation switching by means of a shorting link in the relevant XMS pickup head.

The surprise is the late date of June 1951. By that time, the Deccalian was already on the market and being exhibited at the Festival of Britain. Maybe Decca just kept the circuit details confidential for a while before deciding to publish.

If there are more pages from the same source, it would certainly be interesting to see them. That period of the introduction of microgroove discs alongside 78s was historically important, and one where Decca were 2 or 3 years ahead of rivals EMI.

Martin.