Thanks for the Cambridge T55 (candidate) and Clarke & Smith (959) additions to the list of D&W FM front end users.
That the Cambridge T55 and Sugden R21/R51 front ends were identical strongly indicates that they were third-party units, and I think adds some weight to the notion that they were from D&W.
The Clarke & Smith case is interesting in that as a Mullard Module IF strip was used, one supposes that a D&W front end was chosen over the more obvious Mullard Module because it had better performance. Lower cost seems less likely as major producer Mullard was probably in a position to match competitor pricing as required.
Oscillator-low (infradyne) operation was in fact the original BREMA recommendation in respect of the 10.7 MHz FM IF. As oscillator-high (supradyne) was the norm in the USA and elsewhere, I suspect though that many UK makers, with the export market in mind, followed this pattern. Clarke & Smith might have been more UK domestic-market oriented. I’d guess that D&W would have supplied its FM front ends for either infradyne or supradyne operation as customers required.
As to tuning range, the Radford and Rogers FM tuners had full coverage, 87.5 or 88 to 108 MHz. Initially anyway the Sugden R21/51 covered the “European” range 88 to 104 MHz. Presumably the D&W front ends could be configured to suit.
D&W was very early in adopting dual-gate mosfets for FM front ends. Whether it also went through an intermediate jfet stage in the transition from bipolars is unknown, but the available evidence suggests not. The use of jfets in FM front ends preceded the use of dual-gate mosfets by around a couple of years.
The FET front end option for the Radford FMT2 was available by the time of the Audio Fair 1967, a year after the model was first introduced. The working assumption is that this was the D&W mosfet unit, although it might have been otherwise.
On the other hand, Mullard seems to have been slower in adopting fets for its FM front ends, and I think that it started with a jfet RF amplifier.
Eddystone used a Mullard FM front end in its 1002 broadcast receiver of 1972. This was shown in the schematic as an all-bipolar, 3-gang, varicap-tuned unit. Oddly, it was followed by two dual-gate mosfet IF amplifiers before the CA3089 FM IF subsystem IC. Assuming that Eddystone preferred to use a Mullard unit, one imagines that it would have used a mosfet-based unit had such been available, but absent that accepted what Mullard had available.
The replacement for the Eddystone 1002, the 1570 of 1978, also used a Mullard FM front end, shown as the UM1181 without circuit details on the schematic. I understand that the UM1181 had a dual-gate mosfet RF amplifier, although I have not seen the full circuit. In this case the front end output went directly to a TDA1071 subsystem IC.
As Larsholt has been mentioned, here is the schematic for its 8319 FM front-end. This was of the single-RF stage, four-gang type with a bandpass interstage.
Cheers,