The 74XX160/74XX162 is the decade divider that runs at maximum
clock rate for the chip.  Meaning no external feedback is
necessary to make it work at divide by 5/10.

The 74XX161/74XX163 can only divide by powers of 2 at maximum
clock rate.  You have to add feedback to divide by 5 and THAT
is what slows it down so much.  Dividing by 10 is even slower
in most logic families.

There is also 74XX190 series.

Rick N6RK

On 7/11/2020 3:00 PM, Perry Sandeen via time-nuts wrote:

Hi

HC is the slower version of AC. If it makes it to 50 MHz, you are doing well …..

Bob

Hi Perrier
https://www.y-ic.es/datasheet/3b/74F569SC.pdf   will work
73
KJ6UHN
Alex

On 7/11/2020 3:00 PM, Perry Sandeen via time-nuts wrote:

A long time ago I used a 74AC74 to prescale a 100MHz VCO down to 25, the
74AC74 was AC coupled to the VCO and the signal was a fraction of a volt.
Worked quite well.
Probably not time-nuts quality but in a pinch it did the job at the time.
Didier

On Sat, Jul 11, 2020 at 9:37 PM Alex Pummer alex@pcscons.com wrote:

Hi

One very simple “fix” for the low voltage sine wave:

Put in an L network and transform the load output to a higher
impedance. Voltage goes up as square root of impedance change.
For modest (2X ~ 4X) voltage changes, the lowpass L network still
has modest Q and low component sensitivities.

Bob

Hi,

A similar approach is used in the 10811 replacement oscillator setup for
the 5065, where a 7474 is used to divide 10 MHz to 5 MHz. Signal
conditioning consists of a DC-blocking cap and a pair of resistors to
bias the mid-point. The produced noise is at least 10 dB worse than you
would expect. This impacts long term stability response as I have
reported earlier.

At least using the square-up design in TADD-2 would help, even thought
that one won't work for 100 MHz, so it needs a bit of tuning. There are
chips that solve this.

Cheers,
Magnus

On 2020-07-18 14:31, Didier Juges wrote:

On 7/18/2020 6:25 PM, Magnus Danielson 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.

OTOH, that circuit works well with 74ACXX circuits.  We did that
at 80 MHz in the 5071A and it worked well.

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.

Rick N6RK

Hi Rick,

On 2020-07-19 04:30, Richard (Rick) Karlquist wrote:

Sounds very reasonable. It's a crude hack and works OKish, but to fix it
not much would be needed to be done.

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.

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

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