Daniel Jackson wrote: > "Have you already considered 7360's or 6AR8's as demodulators?" > > Well I have looked at the 12AU7 and wondered if it would go up high in > HF. But two Pentagrid convertors seem most likely.
I believe they could, or still better, 12AT7's. But pentagrid converters may be noisy, and have little gain. Only the newer ones, like the ECH81 seem to be the best performers. I would not bother with 6A7's, 6K8's and 6SA7's. > I will get my RCA Tube handbook and look at the 7360's and 6AR8's. Those are switched beam tubes. The 6AR8 is from the fifties, and the 7360 was the choice of balanced modulator of many radios in the late sixties and 70's. It would be interesting if you have them at hand. Once I bought cheap a pair of new 6AR8's, still in their boxes, for a receiver project. But never found the opportunity to go ahead with it. The 6AR8 was meant to be used as NTSC chroma demodulator. There was an interesting article on QST sometime in 1972 of a 75 meters receiver using a 7360 mixer and a low mu grounded grid RF amplifier with sharp tunable RF bandpass filters aiming to achieve a high IMD intercept. Some radios substituted the 7360 for MC1496 in the mid to late 70's. Nowadays the best alternatives seem to be around the newer high speed CMOS switches. But I have used the old 4066's with good results on 40 meters direct conversion receiver using a polyphase phase shifter for sideband rejection. It worked surprisingly well. I generally look for easy to get parts or some that I may have in my scrounged parts boxes. It is not always worthwhile to spend a lot of money just for the sake of fashion. I tend more to judge if the performance it offers is something I would like to have, at a reasonable price. For me, good and affordable have to go hand by hand. 73, Jose, CO2JA
