[time-nuts] 74AC logic differences between manufactures

[Stanley Reynolds]

Learning about the differences between families now know why a 74F is not a 
substitute for 74AC.

But remembering something I read in Brooks Shera, W5OJM GPSDO notes "Take care 
about which 4046 chips you use for U1 and U3. The Phillips 74HCT4046 chips 
(formerly sold by Radio Shack) are fine. So are CD74HC4046 chips made by Harris 
or T.I. Do not use chips made by Fairchild and do not use CD4046 chips; both 
have a different design and will not work in this circuit."

Does anyone know about any differences in Fairchild and National Semiconductor 
74AC175PC ?

Stanley