I found this schematic in a pile of old books and diagrams I purchased at an estate sale. Must be early since it uses germanium transistors. Runs on 2 x AA cells.
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I notice the circuit incorporates positive feedback. Looking at the entire design, can anyone please tell me if this means it was intended to oscillate, as opposed to being a pure amplifier?
Also, what is the function of the interstage chokes? No value for these was given.
The input and output being loop coils of a few turns looks a bit strange and mismatched. I have no idea regarding the purpose of these.
Looks to be the same operating mechanism as the tube one you posted. I.e., probably nothing at all...
If CK722 fT is enough greater than the tank resonant frequency, the first transistor will probably oscillate (via C-B capacitance, tuned base configuration). If not, it's possible the "output" will feedback into the "input" by proximity.
The impedances are all quite high, implying poor bandwidth (even for CK722) and very little action at all.
If it does anything at all, it's likely a matter of the environment between the coils, not so much the circuit itself. Primitive RFID? Proximity detector? Metal detector? Regenerative radio without the speaker?
If they're between 1 and 100 turns of wire in the size shown, they'll do SFA to the impedance of much larger (kohm) resistors in series.
You'll see the same kind of thing in new designs, throwing ferrite beads anywhere possible -- including places where they actively make the circuit worse, not better. Somewhere between paranoia and superstition.
A coil is a bit higher quality than a ferrite bead, but the impedance is comparable: some kohms at the self-resonant frequency. Which is probably a much higher frequency than the transistors can operate at. At lower frequencies, they'll be a few ohms reactance, or hundreds of ohms, which does nothing compared to the 10k or 220k resistors.
So then, it may be a primitive transmitter. Given the 1940's date of the circuit, would there be any technical or production advantage using a regenerative approach rather than amplitude modulation?
Is it possible the chokes may contribute to the regenerative effect through their radiated field?
One more point.
There appears to be a couple of tunable plate capacitors across the input coil. Any indication what effect these may have on the output?
"Transmitter" would be pushing it. It might make a sine wave. It won't travel any distance.
It surely would not have been in production. A hobby project, probably.
Look, what are you trying to read into these things? It's a pile of parts, not optimized for anything obvious. At best, it's an example of accidental design, not top-down intent. It's no more enigmatic than an audio amp someone tacked extra wires onto. It's very uninteresting, which makes your interest in them perplexing.
Perhaps you could explain what your interest is? Then we could try to provide answers that are more meaningful to you.
No, they don't have enough impedance, and they're too small to radiate per se.
Also, without a mechanical diagram, it's impossible to make any guess at coupling between any of the coils, including the "large" ones (which don't have any winding info at all, remember).
I don't think it was necessarily drawn by a madman or crackpot electro-healer; looks like it was drawn by a teenager/newbie who wanted to make their own shit but didn't quite have the theory down to do so yet, so it's a mishmash of things they'd seen but weren't really appropriate.
I'd have a bunch of drawings/Spice files like that from back in the day if I'd bothered to save them.
Like the tube version a few days back my guess is some kind of pseudo science medico nonsense. You use it in conjunction with a nearby AM broadcast radio receiver and listen to weird whistles and whoops from the device. The two spaced antennae/loops are so you can wave bits of your body in the space between and imagine from the change in tone that you have diagnosed or cured without malady afflicts?
The CK727 PNP germanium probably didn't have a nominal beta of more than around 20, and the curve of beta vs. collector current probably headed straight for the dirt at low collector currents. 220k ohms from 3 volts to the base won't provide anywhere near enough base current to bias the transistor into any kind of operating point sufficient for HF work, and if it turns on at all its operating point will be totally unstable wrt temperature, anyway.
That reminds me of something I read in TIME magazine in the days when transistors were where robots are today - widely used in some fields but still mysterious cutting-edge technology to most people (Iron Man comics often mentioned transistors overheating). The article spoke about an exhibition in which some piece of techno-art wowed visitors by emitting whoops, whistles and lights when they went near it.
On another scrap of paper the input coil is specified as 7T 2 1/2" dia. and the output 7T 6" dia. Presumably air core close wound on a former.
I was hoping to find something unusual, mostly just as a learning experience. The schematics were in fact drawn by an electrical engineer (now deceased).
No feedback there... See Rd and Cd? They decouple the battery supply to the first two transistors. The whole circuit is probably a TRF radio reciever of unknown frequency, since no values are given for the input tuning tank.
Hmm.. someone else was collecting circuits, this one was also in the doc I posted a link to. If you don't know what these circuits were for, you might be in for a surprise...
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Ran into stuff like this about 25 years ago, wild claims, circuits that looked like amplifiers but supposedly did magical stuff. Actually built the 2-stage pentode circuit, added a gain control and output control, input and output jacks, (filtered!) HV supply - awesome guitar overdrive. I used 12SJ7 tubes. As far as the claims.. well it made me feel good when I played through it...
+1 The R and choke at the base look like bias setting R+filter L. They're connected to the supply and not the E. It's just a bunch of common emitter amps.
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