[time-nuts] HP5061B Ion Current

[Donald E. Pauly]

It looks like that there is about 10% hysteresis on the cesium trip
off/on. That may not be enough to prevent cycling on and off.   I may
not have made it clear but instability in the +3,500 voltage makes a
big difference in the threshold ion current required for activation.
If it fades it can require a 10 uA smaller ion current to activate
cesium.

---------- Forwarded message ----------
From: John Miles <john at miles.io>
Date: Tue, Mar 21, 2017 at 5:41 PM
Subject: Re: [time-nuts] Fwd:  HP5061B Ion Current
To: Discussion of precise time and frequency measurement
<time-nuts at febo.com>, rward0 at aol.com


That's some very nice work, Donald.  Looking back, I have junked one
or two Cs tubes that might have been usable if I'd thought through the
problem of high ion pump current as you and KB7APQ seem to have done.

Another good reason to raise the lockout threshold would be to cut
down on the repetitive ionizer filament cycling that the tube will
otherwise undergo when you first fire up the oven.  That phenomenon
always makes me reeeeally nervous.

-- john, KE5FX
Miles Design LLC

> -snip-
> When we overrode the cesium lockout at 29 μA or so of ion current, we
> needed only minor front panel adjustments for beam current of 20 μA.
> (We shorted across A15 R-4.) Our last ion current before power supply
> modifications at risen to 39 uA.  Beam current has been stable.
>