I just stripped one of these units out of an Argo Systems AS-210 to use
as a stand alone reference.
The system ran before I did this, so I was sure all the hardware was
working.
It is marked FRK-L (manual says this the low temp operating version),
and says
Efratom p/n 2A5A2A.  I did not see any data in the factory manual for
what this might mean,
but it has the coax 10MHz, and pins for #2-9 connections.

My issue is that this has wires attached to pins 8 and 9, the *optional
remote frequency adjustment.
The label says "Unit Wired For Operation With External Frequency Control".
*This is discussed nowhere in the 79 page manual, and I have no idea
what to do with these connections.
the option is listed as a possible one, but nothing further is said, and
no connections to it show up anywhere.

Any information is very welcome, as I would like to make a back up Rb
standard for my bench and this
looks like a great candidate if I can get it running.

Also, from a waste heat viewpoint, the supply range is 22-32VDC, the
schematics discuss an internal +17VDC bus,
so am i correct in thinking that a well regulated +22-24VDC supply is
better than a +28VDC one in terms of waste heat (and shortened life)?

many thanks,
walter

Walter Shawlee 2
Sphere Research Corp. 3394 Sunnyside Rd.
West Kelowna, BC, V1Z 2V4 CANADA
Phone: +1 (250-769-1834 -:- http://www.sphere.bc.ca
+We're all in one boat, no matter how it looks to you. (WS2)
+All you need is love. (John Lennon)
+But, that doesn't mean other things don't come in handy. (WS2)
+Nature is trying very hard to make us succeed, but nature does not depend on us.
We are not the only experiment. (R. Buckminster Fuller)

If you look at the schematics of the C-field adjustment circuits, you'll
find where the tweaking is available for fine tuning the Rb system. I
think that's the only "frequency adjustment" spot to worry about. The
other is the tweak for the crystal oscillator to accommodate long term
drift there, if its tuning range hits a limit. This an internal, seldom
needed adjustment, so the C-field is likely the only one that would be
useful externally, to (very) fine tune the output frequency. I have some
similar M-100 units, which have access to the C-field pot through a hole
in the back end heat sink and case. An external adjustment port would be
either a substitute for the internal pot, or something to add to or
subtract some current from the C-field coil, that's mostly controlled by
the internal pot.

So, look for an internal pot. If there is one, then the external stuff
likely just modifies what it does. If there isn't one at all, then the
external circuit may have to provide the proper current, so it may be a
little more complicated. It could also be that the C-field is set up to
some nominal value, with fixed resistors, without any internal pot, and
an external one just moves it around a bit.

If you just run it, and it locks, it should be good to go, and you can
figure out these fine tuning issues later.

Ed

In the last few years, I've obtained 3 FRK's and all 3 had the same issue.
The C-field voltage was so far off from where it needed to be that the servo
loop wouldn't lock up.  In all 3 cases, I was able to get them working by
changing out resistors R17 and R20 in the C-field circuit on the power
supply board.  Other resistors in the same area, R16, 18, and 19 might come
in to play too.  In at least one of the units there was also a wire that
needed to be moved and possibly a jumper that had to be removed or added.
This is all very easy to do as it's on the top side of the power supply
board, and the resistors are mounted on terminals to make them easy to
change.

My guess is that the FRK's were installed in some larger system that used
the external EFC input and when the FRK's were pulled they were not
configured properly to be used standalone as I am using them.

I probably took some notes on exactly what I did to get them working.  Let
me know if you need any details and I'll see if I can find (or remember)
exactly what I did.

Good luck,

Rodger

-----Original Message-----
From: ed breya eb@telight.com
Sent: Wednesday, September 22, 2021 2:15 AM
To: time-nuts@lists.febo.com
Subject: [time-nuts] Re: Some assistance with Ball-Efratom FRK-L Rb Osc.
Needed

If you look at the schematics of the C-field adjustment circuits, you'll
find where the tweaking is available for fine tuning the Rb system. I think
that's the only "frequency adjustment" spot to worry about. The other is the
tweak for the crystal oscillator to accommodate long term drift there, if
its tuning range hits a limit. This an internal, seldom needed adjustment,
so the C-field is likely the only one that would be useful externally, to
(very) fine tune the output frequency. I have some similar M-100 units,
which have access to the C-field pot through a hole in the back end heat
sink and case. An external adjustment port would be either a substitute for
the internal pot, or something to add to or subtract some current from the
C-field coil, that's mostly controlled by the internal pot.

So, look for an internal pot. If there is one, then the external stuff
likely just modifies what it does. If there isn't one at all, then the
external circuit may have to provide the proper current, so it may be a
little more complicated. It could also be that the C-field is set up to some
nominal value, with fixed resistors, without any internal pot, and an
external one just moves it around a bit.

If you just run it, and it locks, it should be good to go, and you can
figure out these fine tuning issues later.

Ed

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instructions there.

Walter, at least in my FRK manual the External frequency Adjustment is
addressed on page 4-7.  In brief you connect a 1k0 variable resistor
between pins 8 and 9 as you have the variety with those connections.  I
have a pencilled note saying that you may need to add some components
internally.  The Power Supply schematic page has the details.

Personally I don't think it is worth adding; I did it to the FRK in a
Racal 9475 standard and it has not needed attention in maybe ten years.

Best fire it up and see if it locks reasonably quickly (ten minutes?). 
There is a triangle wave that sweeps the 10 MHz oscillator as it warms
up, if you monitor the 10 MHz output you will see the effect of that. 
There are areas that may need looking at, for example there is a free
running CMOS oscillator around 8 kHz in the synthesiser that may have
drifted.

Years ago there was some discussion on this list about the best supply
voltage and heat sinking, it may be worth finding that.

Dan