View Single Post
Old 27th Jun 2019, 2:55 am   #12
Synchrodyne
Nonode
 
Join Date: Jan 2009
Location: Papamoa Beach, Bay of Plenty, New Zealand
Posts: 2,943
Default Re: Dormer & Wadsworth (D&W)

Quote:
Originally Posted by Radio Wrangler View Post
What I did wonder about was where all the innovation came from. The answer I saw was the semiconductor firms. What became the norms in FM tuners came from the applications notes of RCA for dual-gate MOSFETs, CA3089 and CA3090. Motorola for varactor tuning and MC1310. Philips ar the time were producing reference designs around bipolars saying that they represented the best performance on low DC bias currents - clearly thinking of portable. radios, not hifi. Ceramic filters came along and became standard features. Did this come from Murata/Kyocera? or were Brush-Clevite the initiators? Murata were certainly the winners.
With the ceramic IF filters for consumer equipment, Clevite does appear to have been the initiator in the early 1960s, at least for AM applications. But by the time they came into widespread use for FM tuners and receivers, say 1969 give or take, Murata was probably the dominant supplier, and by then I’d expect doing its own R&D.

RCA’s several steps along the road from all-bipolar to all-dual gate mosfet front ends were mentioned in post #1.

The use of jfets in FM front ends turned out to be something of a side-story. TI could have been involved as a proponent, although not the only one. It did pursue the use of jfets in TV front ends, but that was not productive, although the specific drawbacks, whilst being deal-breakers for the TV case, were manageable for the FM case. But by 1970 it was advocating the use of dual-gate mosfets in FM front ends.

In respect of the development of integrated FM IF strips, RCA was a major contributor but not quite as dominant in early innovation as it was in the dual-gate mosfet case. It went through several intermediate steps before it got to the CA3089. In coarse terms, and referring only to the FM-oriented ICs (not those with a TV-sound orientation) these were the CA3012/CA3014, the CA3043, the CA3075/CA3076. The CA3089 was the first RCA own-design FM IC to include quadrature demodulation. Fairchild had previously introduced a rudimentary form of quadrature demodulation in its µA717, but Sprague was the first to use a balanced six-transistor tree for the purpose, in its ULN2111A. This spawned many lookalikes, including but not limited to the SGS TAA661 and Siemens TBA120. RCA’s master stroke was to develop a complete subsystem, inclusive of auxiliary functions, in an IC that included a quadrature demodulator and had extra gain as compared with what had gone before.

Sprague had also noted that the six-transistor tree had multiple uses, and Motorola took this on board in a big way. One of its several early applications was in the MC1304/5 stereo decoder IC, which I think established Motorola’s prime position in this field. RCA was first with a PLL-type stereo decoder, but Motorola followed this very quickly with its own MC1310, which became the dominant type. I’d guess that Motorola built on its established position, added to which its decoder did not require the use of an inductor, whereas the CA3090 did. Anyway, the equipment makers seemed happy enough with using an RCA/Motorola combination rather than an all-RCA set of ICs. Fairchild also introduced a PLL stereo decoder, the µA758. I am not sure whether this just preceded or just followed the MC1310, but in the literature it has often been treated as an MC1310 variant/derivative, perhaps not because that is what it was, but because of Motorola’s dominance.

During the 1970s, once the plateau had been reached and refinement rather than significant innovation became the mode, both RCA (CA3189) and Motorola (TCA4500) offered improved ICs in their respective fields, but Hitachi and Toko moved into dominance, each offering successively improved versions of both the CA3089 and MC1310, with some selective innovations such as pilot-tone cancelling decoders. Toko was by then a major coil and IFT supplier, and also offered block filters for pots-decoder filtering, birdie filtering, etc.

The arrival of fully electronic tuning towards the end of the 1970s, which required changes to the IF ICs, apparently provided an opportunity for Sanyo to emerge as a major force, at least somewhat displacing Hitachi and Toko. National Semiconductor also entered the FM IF IC field with its LM1865 family, which was innovative in having an on-board IF pre-stage and providing dual-bandwidth front end AGC.

Quote:
Originally Posted by Radio Wrangler View Post
D&W were but a step in this food-chain... the trickle down from apps notes.
My guess is that D&W may have started with say a Mullard-based all-bipolar design, although the double-tuned bandpass input option might have been its own idea, in order to get better resistance to spurious responses for the hi-fi market. Then it followed the RCA application notes when it came to converting its circuits to use one or more dual-gate mosfets. (I think that the European semiconductor makers were asleep in the late 1960s when it came to developing and applying dual-gate mosfets.) After that it followed the Motorola application notes when it came to adapting its circuits to use varicaps.

It also reasonable to assume that D&W saw a market opportunity for FM front ends that were somewhat better than those offered by Mullard, and suitable for use in hi-fi tuners. It could have been a niche that was not addressed by the “major” TV front end makers, such as AB Metal Box, Plessey-Brayhead and Cyldon. In the valve days, some of these at least also offered FM front ends, but these appear to have been of the basic one-valve, two-gang variety that was probably at best marginal for hi-fi applications. And with solid-state TV front ends, they stayed with bipolars well beyond their “best by” date, so even had they FM offerings, they probably would not have had the mindset necessary to make the change to mosfets – perhaps some NIH at work. D&W’s main competition in the 1960s may have been the German makers such as Görler.

From this distance looking back, D&W is very obscure. It is the sort of organization that “Hi-Fi News” magazine just might have written about back in the days before it went off the rails, and had quality columnists such as Austin Uden, but as yet, there is no on-line archive for this magazine.


Cheers,
Synchrodyne is offline