[time-nuts] HP5061B Ion Current

paul swed paulswedb at gmail.com
Wed Mar 22 11:50:38 EDT 2017


I am listening and learning. Great point on the HV supplies.
When I look at the supplies I believe they are soldered cans. Is that
correct?

Further had not thought about the ionizer. Skips pictures of the CBT tube
clearly shows a popped ionizer.

There are two oven controllers AC or the DC version. I would strongly
believe the DC is quite easy to control through a FET and monostable. But
this approach simply prevents multiple trips if the ION pump is re-cycling.
AC maybe a bit harder. Have to actually look.

On Frankenstein I built a DC controller not realizing HP used DC in later
models so on that unit its very easy to do a soft start ramp.

Regards
Paul
WB8TSL


On Wed, Mar 22, 2017 at 9:33 AM, Scott McGrath <scmcgrath at gmail.com> wrote:

> 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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