[time-nuts] HP5061B Ion Current

Scott McGrath scmcgrath at gmail.com
Wed Mar 22 09:33:01 EDT 2017

John makes a good point about the ionizer filament has anyone done a 'slow start' system for the Ionizer filament?   

I.e. Limit the inrush current as is done for expensive high power transmitting tubes?

> On Mar 21, 2017, at 9:44 PM, Donald E. Pauly <trojancowboy at gmail.com> wrote:
> 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.
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