What to do with a CK722 in 2024?

[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

[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?