Old Transistor Circuit - Positive Feedback Question

And you think the positive feedback is where?

It looks (given all the chokes and input loop/variable caps) that it was intended to be an RF amplifier probably in the AM radio band. Since CK722 were audio transistors this circuit was doubtless a fail. Possibly, the input coil might have been a "loopstick" antenna.

The output "coil" may have been headphones if it was intended to be a radio with detection at one of the transistors. But the various chokes seem to say otherwise. In those days usually CK722 "radios" used the base junction of the first transistor as a detector and the rest were simply audio amplifiers. Basically a crystal set with an audio amplifier.

Reply to
benj
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CK722s didn't have hard Ft specs, but some would work in the AM band, and some were reported to oscillate as high as 3 MC (megacycles in those days.) Regenerative receivers were done.

The inductors in this circuit may have peaked the HF gain a bit. Inductors and transformers were cheaper than transistors, and gain was expensive, so a lot of old circuits had L or T interstage coupling.

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John Larkin         Highland Technology, Inc 
picosecond timing   precision measurement  
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Reply to
John Larkin

My father was a Raytheon wholesaler... so, by 1956, I had access to CK722's and CK760's. I had a real nice 'portable' radio with a 6x8 oval speaker, and CK760's for the front-end and the 455kHz IF (transformer-coupled, with a winding tap for 'neutralization'). ...Jim Thompson

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| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
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Reply to
Jim Thompson

"Jim Thompson" wrote in message news: snipped-for-privacy@4ax.com...

Should the base of the first transistor go to the junction of the two variable caps to get a bit better matching?

Reply to
tom

I have some PNP germaniums from maybe the late 1950s in my junk box, don't remember where I got them. I've never tried to do anything with them because at least via testing with a modern digital multimeter diode test all the base-emitter junctions appear to be blown open, unless for some reason a modern multimeter's diode test won't work on them. It works on germanium diodes, though.

Reply to
bitrex

Possibly. The radio I had actually did one of those oscillator/mixer tricks for the front end and there was a tap on the loop-stick, rather than a capacitive tap (which complicates biasing). ...Jim Thompson

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| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
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Reply to
Jim Thompson

Yeah, their CK760 were a transistor line specifically developed to give the bandwidth needed to build transistor radios.

Reply to
benj

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