The circuit linked below appears to be a conversion of a three stage inverting tube amp tube to a transistor circuit, powered by 3VDC.
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It appears to be intended to capture high frequency ambient signals and re-broadcast them. It may also be designed to self-oscillate to add a carrier wave.
In any case, I would like to build it out of curiosity to see what it does.
Can anyone please explain the function of the inductors, and what might be a suitable value for same?
What would be a modern equivalent of the CK722 PNP Germanium transistor?
Perhaps. Or maybe the output coil and input coil are lightly coupled by distance and maybe it is a metal detector?
That is admirable.
I think Tabbypurr explained the function.
Values. Hmmm. Well, the dia is .25" and the length is .75". No magnetic core is indicated so that's pretty much all we have to go on. Maybe it is air-core? What wire size shall we use for an estimate? Let's start with #30 AWG.
I calculate the inductance could be 10uH with 75 turns on, say a wooden dowel.
That's difficult. My bet is that the 722 did not have much HF gain so using some other device may have its consequences.
You can buy (for collector's prices, link below) the original transistor. Otherwise, I suggest you search for germanium PNP transistors. If it were me, I'd just try it with a jellybean PNP, (whatever you have on hand) just to see what happens. That's your aim anyway, yes?
You have a larger problem facing you. There is nothing to indicate the "Well" and "Plate" coil characteristics. Also, there seems to be no indication of value for the "Rate" cap variable capacitors nor the pot below them.
My guess is those were section wound ferrite* chokes of 5-10mH. Since they are in series with 10k resistors that puts a slight gain peak at
100-150kHz just where the CK722 could start to roll-off. Judging by the interstage capacitors 50-70pF that implies operation frequency might be in the 100kHz region. Alternatively the chokes were intended to couple to each other as a poor mans transformer?
Was the app underground potholing/mines communications repeater?
piglet
Like ebay item "Vintage J.W. Miller CO. #6302 Ferrite Choke 2.5 MH 200 MA New Old Stock"
Low current doesn't help the tr's hf response - which presumably is lousy at the best of times.
From 1952 CK722 datasheet - which is rather brief: Abs max: Vce 20v, Ic 5mA. Pdiss 30mW @ 30C amb. Tamb max 50C. Average gain characteristics: Vc 1.5v, Ic 0.5mA, Ib 20uA, beta 12, power gain 30bD, NF 22dB@1kHz. With 1k source, 20k load.
There are tons of ex-Soviet germanium PNPs on eBay for cheap, and it should be possible to find a cross-reference. Many Soviet active components were spec-copies of US devices anyway..
In 1955 one paid a heavy premium for transistors, so the finished device must need portability & low power consumption.
All the chokes oriented the same means some coupling is inevitable. I don't know if it's worth looking at which paths create nfb & which pfb. Low frequency might make this minor, I don't know.
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