[time-nuts] HP 5065 Rb update

[paul swed]

Hello to the group.
Did switch the leads and no major effect.
I also did provide a separate power supply and am controlling the cfield
with that. It appears that by going to 7 ma the system is stable on the
original tube marking of 8714 on the thumbwheel. The original cfield range
went up to 6.6 ma. Literally adjusting the current resistor in the cfield
regulator will put it back into range. But thats still easily a 4ma jump to
get it back to normal.
Ed to your comment the pot could be expanded though with readings I am
getting may be just fine. It seems to be approx 5.0 E-12. Its a simple 1K
pot with digital dial readout that feeds a diff transistor and driver
transistor. Quite simple.
That said with the external supply sort of slapped in at 7.28 ma the unit
is 5.6 E-10. Clearly not stable but the supply is a tek unit etc. I at
least now know the range the cfield might want.
*But does it matter that I use a different thumbwheel setting if the
results are solid*?
Regards
Paul
WB8TSL

On Sat, Dec 5, 2020 at 2:41 PM ed breya <eb at telight.com> wrote:

> If the only problem is that you're at the resolution limit of the pot,
> you may be able to slightly modify the circuit, reducing the pot's
> effect, but also reducing the total adjustment range. I don't recall
> what the circuit looks like, but from the discussion I'm guessing it's
> like a 10 kilohm or so ten-turn WW with a kilodial on it, and it adds
> some adjustable current to the C-field network. The few k ohm range pots
> have set-ability that's near the small tick dial resolution. If the pot
> is quite low resistance, like less than 2 k, it can be much worse, due
> to the larger resistance wire - the wiper can only interpolate so much
> between the discrete wire turns, so the net value has more ripple with
> rotation. If the pot is in the few k region, you can gain quite a bit of
> actual resolution by upping it to say 50 or 100 k, but of course the
> rest of the circuit would have to be adapted.
>
> Ed
>
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