Yann Guidon / YGDESTTL is just a modification of DTL, itself derived from RTL...
In 1967 you could purchase this chip for about 11USD. Barely enough to build a dumb flip-flop.
Note that ECL would also use transistors as input buffers / impedance adapters but the amplification chain is different and DTL/mDTL/TTL saturate and have a much higher signal swing, much better noise immunity and ... longer cycle times.
The other difference with ECL is the use of complementary transistors, which make it harder to build with old transistors since they are mostly one polarity only. But it's a nice little circuit to analyse :-)
SRC: https://www.facebook.com/photo/?fbid=1419577419961171 (thanks to the author of the macro pictures)
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You could shell out that much money for it, but in 1967 you could already get 54 and 74 series TTL chips that included flip flops and a full adder, see index page 0003 of this catalog: https://ftpmirror.your.org/pub/misc/bitsavers/components/ti/_dataBooks/1967-68_TI_Integrated_Circuits.pdf So buyers would be using them as spares for military equipment. A search found an auction for these chips, stressing that they contain gold and are rare. (That same search also returned a link to my #DTL binary clock project which exhausted my stock of DTL chips, except for some logic gates, so I'm out of the game.) It's interesting that the SN53 family was described as modified DTL. The next step would be the multi-emitter structure to get TTL.
Edit: In fact a search shows that the multi-emitter structure was invented in 1961 and by 1967 was standard. I've in fact already referenced this article in a log post in my DTL clock project: https://computerhistory.org/blog/the-rise-of-ttl-how-fairchild-won-a-battle-but-lost-the-war/#:~:text=Independent%20inventions%20of%20TTL,familiar%20to%20many%20computer%20designers.
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Thanks for the context !
it's unfortunate that multi-emitter structures are not easily available as discrete parts :-P
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Having a lot of old parts is a bit of a curse. I'm constantly thinking of ways to try to use them up when arguably it's better to just e-waste them and get on with new-fangled tech. That's why my policy is not to buy NOS before using up OOS.
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