odd variable capacitor ?

After checking out the patent no. 1626391, I misread the number previously. It was patent in 1927 so I guess it was for TRF receivers, giving them a wider tuning range and perhaps a neater dial cal. Does anyone recall who might have used them? tnx

There was an article in Antique Radio Classified some years ago that made me aware of capacitors with tapered plates.

You can look up that patent online

A variable capacitor with semicircular plates and the axis of rotation going through the middle and flat plates gives of course a linear relationship between capacitance and angular rotation. By altering the plate shape a bit and moving the axis of rotation off-center you can get a capacitor that tunes straight-line wavelength. Wavelength is proportional to the square root of capacitance. In the early days of radio wavelength was often specified instead of frequency.

You can make a variable capacitor that is straight-line frequency, which rotation has to be proportional to the reciprocal of the square root of capacitance. With flat plates this requires a fairly radical plate shape, with the axis of rotation very far off center. As a result there has to be a lot of empty space for those long narrow plates to swing around. I'll post a picture of one of these to that binaries group.

So a way to get around the odd plate shape and the space it occupies is to use plates of tapered thickness. It would be nice if you got straight-line something, but even if you don't you have something where the stations are more spread out than they are with straight line capacitance.

I have an old TRF receiver of the vintage of multiple knobs and 01A tubes that uses capacitors like this.

Jim Who made your TRF with this cap and are the dials calibrated, if so f or wavelength? tnx

--

Hallicrafter, Telefunken, Nordmende, etc all used similar caps in their TRF recievers, as did ARC5,ARC 7, and quite a few of the communication transcievers used in the late 30's early 40's. I had operational ARC 5 and ARC 7 with the external Antenna Tuning box in the late 50's. Made nice QRP devices excepting the QRM generated.

Well, it's a mystery. There is no manufacturer's name on it anywhere. And all the parts are from various well-known parts vendors (except no labels on the coils). There are several theories: Might be a home-built set - if so, it's incredibly well done, including an engraved front panel Might be built from a kit - but then you'd think the kit manufacturer would have put a name on it somewhere. Might be a factory-built set for some department-store chain that was to attach their own brand label, tho there is no evidence that one ever was attached. Might be a factory-built set and the maker is deliberately non-identified to avoid paying royalties on the Neutrodyne patents. Which could also apply to a kit. I read some early superhets were sold as kits to get around paying patent royalties. Someone suggested a fly-by-night manufacturer, who would come into a village with a wagon load of receivers, and secretly bring another wagon with a transmitter. The transmitter would assure they had a good signal while they were selling the receivers; and once they were all sold they could move on. However this receiver is certainly not shoddily constructed.

Any other theories?

The dials are not calibrated in frequency or wavelength. They look like National vernier dials, calibrated 0-100.

I have an Allen-Cardwell cap with a plate set that looks sort of like a French curve. It appears irridited (gold-looking color?) and came from a test set of some sort, but its been too long ago to remember...hi!

I know it sounds silly but I work in cable tv and everybody seems to have some 'favorite' oddball channel that they are demanding be carried as part of their service.

-Bill

well, if you had more than one transmitter, you could simply act as a repeater and boost the signal on as many stations as you had transmitters.

but i just dont see it actually happening. sounds crazy.

randy

Heard them at a neighbor's house?