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Old 3rd Jul 2019, 3:33 am   #18
Join Date: Jan 2009
Location: Mt. Maunganui, New Zealand
Posts: 2,506
Default Re: Dormer & Wadsworth (D&W)

Thanks for that. I’d say that it’s better than even odds that A.H. Dormer was the Dormer in D&W.

His comment at the end of the SWM article – about using the Plessey SL620 and SL630C ICs in a modulator circuit - is interesting: “Although circuits have been published in the past showing use of these IC’s [sic] for compression purposes, they seem to have been taken directly from the manufacturers’ data sheets which, in practice, are not always suitable for amateur use.”

That suggests that although he might have been guided by the semiconductor makers’ application notes in designing FM front ends, he also put his own interpretation and ideas into them. I imagine that he would have been able to provide a cogent rationalization for placing the bandpass at the input rather than at the interstage.

Interesting that he used the TIS88 jfet for the microphone preamplifier and its “emitter follower”. This was TI’s contender for TV front end use in the late 1960s, and did find application in some FM front ends (I think B&O used it, for example). One wonders if D&W offered say a TIS88 cascode RF amplifier option for its 341-series FM front end.

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