Hi If you want to get the 74AC74 (or better the 74LVC74) running it’s best:
1) Power it off of 5.50V 2) Transform the drive signal so that it presents 5.5 to 5.8V p-p to the gate input. 3) Bias the AC signal so that it swings from about 0 to 5.5V Bob > On Jul 19, 2020, at 8:18 AM, Magnus Danielson <[email protected]> wrote: > > Hi Rick, > > On 2020-07-19 04:30, Richard (Rick) Karlquist wrote: >> >> Yes, the simple pair of resistors doesn't work well on TTL. >> That was probably done by a production engineer, who was >> working above his pay grade. We can't all be Len Cutler. > Sounds very reasonable. It's a crude hack and works OKish, but to fix it > not much would be needed to be done. >> >> OTOH, that circuit works well with 74ACXX circuits. We did that >> at 80 MHz in the 5071A and it worked well. > > OK, that can be useful to know. I should probably do some tests then. > Maybe replacing the 7474 with a 74AC74 will make it perform better. It's > simple and straight-forward enough, but I would like to measure and > compare to know. Maybe someone already done that. The problem is to > lower the added noise enough, and slew-rate limited signals into a > trigger point is a know source, then the gate itself can contribute > naturally. > > Anyway, thanks for that little insight. > >> >> Back in the 70's when I worked for Zeta Labs, my boss taught >> me to use a 1 transistor buffer that had a pull up resistor >> on the collector and a resistor from the collector to the >> base and a resistor from the base to ground. We used it >> in all our designs and it worked well, despite being >> ridiculously simple. My boss was really smart. >> >> That is what they should have used in the 5065. > > Sure. It's not very hard to do. The 5065A synthesizer input have the > same challenge, so it has higher noise because of that, but if one has a > 00105 oscillator that will cover that up anyway. The 5065A synthesizer > isn't very quite for sure, and just using a 3325B is replacement I > dropped the ADEV floor by over a factor of 2 on a 00105 based 5065A, > because the 3325B lock-up filtered much of the 00105 noise out and did > not have as terrible sidebands and input treatment. That said, the 3325B > isn't particularly "clean" but sufficiently clean to achieve that > improvement. Sometimes "sufficently" is the key word, and applying it > one can get cheap fixes that moves things out of the critical path for > performance. Sometimes all it takes is a 2N3904 or two with a few > resistors and caps. Figuring out where the key performance limiters are > and address those sufficiently well may achieve most of the gain at times. > > Cheers, > Magnus > > > > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
