This was only to scratch an itch of mine to see how the Efratom TS105 stages would work as a standalone Dual Mixer.
I was not trying to build "modern"!
The 1650 or 1651 were purchased on ebay for reasonable prices.
I also wanted something that could be easily assembled as Sometimes that scares people off.
Once I have done comparative testing with different types of op amps and comparators we will see if it has reasonable performance for entry level DMTD work.
First Time interval count and dirty layout for testing PIX.
No problem with "not modern", I was just hoping to have something that is more easily reproducible without resorting to finding "new old stock" on ebay. I don't usually buy parts from unknown sources, I stick to DigiMouser or maybe LCSC for Chinese chip vendors that are not stocked by my usual sources.
Still, when you publish the schematic at a point, I can likely come up with a "modernized" version, easier though if you provide some insight in what parameter was key to selecting a certain part over another.
For the MC1651, I'm guessing any reasonably fast dual channel comparator with differential output will do?
Do you need the latch function of the MC1651 (I'm guessing not)?
Without seeing the schematic, I figure the idea is to drive the mixer from the differential outputs of the comparator, first channel with the 10MHz from the DUT, the second channel from the transfer oscillator? The mixer output is then going into an amplifier and limiter and from there into a logic gate, probably some HCT or AHCT to have a TTL output for the counter.