What to do with a CK722 in 2024?

[Airedale]

I was able to buy a pair of them for only 10 bucks, what do you think I should build with them? Would a single transistor amplified crystal radio be a good idea?

[Phil]

There is a problem with your circuit. There is no bias on the base of the transistor. I don't believe it will do anything as drawn.

[Airedale]

Originally Posted by Phil

There is a problem with your circuit. There is no bias on the base of the transistor. I don't believe it will do anything as drawn.

Is this a viable design?



https://va3ngc.weebly.com/uploads/3/...92131_orig.jpg

[Electronic M]

If you have a strong local station I've seen some crystal radios that are dual tuner where one creates a few volts from the local station to power a transistor to amplify the other tuners output.

[old_tv_nut]

Originally Posted by Airedale

Is this a viable design?



https://va3ngc.weebly.com/uploads/3/...92131_orig.jpg

I think a 1M ohm resistor from the junction of the diode and the 0.02 microfraad to ground may be needed so the rectified voltage can discharge and follow the modulation. Then you might try adding 10 or 20 pF in parallel with the 1M ohm to filter out any remaining RF at that point.

This page offers a couple of alternatives inlcuding one where no diode is used and the transistor rectifies the RF. Don't know if that will work with a CK722. Its response may be too slow to make a good RF rectifer, so the combo diode and transistor circuit is a better bet.

[old_coot88]

You'd also need to bias the base to bring the transistor into conduction (think grid of a triode by analogy). Run a resistor from the negative supply to the base. I'd start with maybe 22K and then go up or down as needed.

Built a few of these back around '58, using the '722's predecessor, the CK718. Anybody 'member the CK768, the first hobby grade RF transistor? Built a cute little regen set with it.

The 718s were "pulls" from hearing aids, evidently for excessive 'white noise', then offered in Popular Electronics for us nerds.

[jr_tech]

All this makes me wonder if the 50th anniversary radio really works as drawn.

http://semiconductormuseum.com/Const...adio_Index.htm

jr

[Alex KL-1]

+1
Even if the CK722 can be leaky at the point of making useful/detectable output/amplification, the diode will be blocked after some RF cycles? Or, the diode can have to be very leaky also?

[Phil]

The circuit on the upper right side of page 3 doesn't appear it could work. The circuit on the left hand side has a resistor to the base and probably would. Also, a .02 seems way too small to couple audio to the base of the transistor. If it were a mosfet it would be one thing but a transistor base isn't that high an impedance. I would go with the circuit showing the resistor to the base of the transistor and increase the coupling cap to at least a .1

[old_coot88]

This is a typical hobbyist setup from '57 using the CK722. The coupling caps were somewhat bigger than .02.
https://archive.org/details/Pop19571...p?view=theater

[Airedale]

So old_tv_nut is this what you are talking about?

https://imgur.com/gallery/qwCPwLI

[old_tv_nut]

Originally Posted by Airedale

So old_tv_nut is this what you are talking about?

https://imgur.com/gallery/qwCPwLI

That has the 1M and 10 pf on the wrong side of the .02 microfarad. Should be at the junction of the diode and the .02.

Also why do you show two grounds? Both grounds should be connected.

[Airedale]

Pardon, I get easily confused. Is this correct?

https://imgur.com/gallery/x5eU7wH

[kf4rca]

When I started fooling around with electronics, the supply of CK722 transistors had already dried up. Pretty much the same with 2N107 transistors.
But the guy at Radio Lab had 2N217 transistors for only 99 cents. They had long leads which was perfect to my style of construction.
It was an all afternoon trek to Radio Lab (next door to WCSC AM-FM-TV station) and back home but it was worth it!

[old_tv_nut]

Originally Posted by Airedale

Pardon, I get easily confused. Is this correct?

https://imgur.com/gallery/x5eU7wH

Yes.