View Single Post
Old 26th Jun 2019, 3:32 am   #8
Synchrodyne
Nonode
 
Join Date: Jan 2009
Location: Mt. Maunganui, New Zealand
Posts: 2,448
Default Re: Dormer & Wadsworth (D&W)

Here is the Cambridge T55 FM front end, with the Sugden R21/R51 circuit for comparison:

Click image for larger version

Name:	Cambridge T55 & Sugden R21,R51 FM Front Ends.jpg
Views:	39
Size:	46.4 KB
ID:	185719

I think that the T55 dated from later in 1972, so it was a bit later than the R21/R51, which were from 1970-71.

In terms of general circuitry, the T55 could be said to have been an early “plateau” model, having dual-gate mosfet RF and mixer stages, and using the “industry standard” CA3089 IF processor (which dated from the second half of 1971) and the MC1310 PLL stereo decoder (which dated from early 1972). The Sugden R21/R51 started life with a discrete decoder, later changing to the MC1310. It also had a discrete IF strip, which I don’t think was ever upgraded.

On about the last step to the plateau was the Quad FM3. In original form it had the two dual-gate mosfet front end, IF strip using the TAA661 IC, and the MC1305 non-PLL IC decoder. It was updated in two stages, firstly with the MC1310 in place of the MC1305 and secondly the CA3089 in place of the TAA661.

Models such as the Leak Stereofetic and Rogers Ravensbourne and Ravensbrook were further back down that staircase from all-bipolar discrete to the plateau. The Ravensbourne was early in having the two-mosfet front end (courtesy of D&W) and had the early Fairchild IC-based IF strip using a µA703 cascade and a ratio detector. The Ravensbrook had an early RCA IC-based IF strip, namely the CA3012/CA3014 combination (which actually predated the µA703). Both had discrete decoders. The Ravensbourne was later updated, but I am not sure of the details.

Returning to D&W front ends, it occurred to me that the Goodman’s models of the later 1960s and 1970s might have been candidates for using them, but a look at the schematics for the Stereomax, Module 80 & 90 and One-Ten models does not show any correlation. The Module 80 & 90 and One-Ten models all had front ends using jfet RF amplifiers, so they might have been of German origin. The German makers seemed to favour jfets during that period.


Cheers,
Synchrodyne is offline   Reply With Quote