I recently saw that Electronic Goldmine is selling new old stock of Signetics NE564N PLL ICs https://www.goldmine-elec-products.com/G25530 .
This brought back memories of my early career in electronics working at the University of Hawaii from 1971-1973. That was a period of time when integrated circuits were just becoming more common and most everything was bipolar. FETs were only available as discretes and were quite costly, so we didn't use them. Motorola introduced their high speed digital ECL (MECL) logic circuits and Intel introduced their 4004 and 8008 microprocessors. On the analog front we were happy to finally get the internally compensated 741 op amps.
That was when I first encountered the Signetics family of phase lock loop ICs which integrated the VCO, phase detector, low pass filter and amplifier. I was quite amazed at the functionality they were able to pack into an integrated circuit. They had two product lines the 560, 561, 562 for frequencies up to 30 MHz and and the 565, 566, 567 for frequencies up to 500KHz. The designs were very nicely implemented. The 560-562 parts all used the same silicon die, but achieved feature differentiation by using different metallization interconnects.
Our lab was working on a feasibility study for a tsunami early warning system. We were trying to correlate Rayleigh waves generated by seismic activity with vertical displacement of the ionosphere. We measured the ionospheric movement by determining the Doppler shift of the 10 MHz time reference signal from WWVH that was reflected off the ionospheric layer. I used the phase detector of the 560 which was basically a double balanced mixer to extract the Doppler shift by beating the received signal against a temperature stabilized reference oscillator.
The circuit worked really well, but unfortunately I lost all of my project documentation due to water damage in the 1994 Northridge earthquake in Southern California - somewhat ironic.....
Anyway, I was interested to discover that this type of research is still being conducted almost 50 years later - albeit with much better technology.
https://earthdata.nasa.gov/learn/sensing-our-planet/warnings-from-the-ionosphere
https://www.nature.com/articles/s41598-018-19305-1
The NE564 is a later version of the NE560. It is spec'ed to run up to 50 MHz. I'm not sure when it was released, but the date code on the Goldmine part is 1983.
I decided for old times sake, I needed to buy a few. Maybe make a more conventional PLL project.
Here's the Block Diagram of the circuit:
It always amazes me to reflect on what we were able to accomplish way back eons ago. And without the Internet 
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