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@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@febo.com>, rward0@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. >

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@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@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@febo.com>, rward0@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. >> > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there.

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@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@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@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@febo.com>, rward0@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. > >> > > _______________________________________________ > > time-nuts mailing list -- time-nuts@febo.com > > To unsubscribe, go to https://www.febo.com/cgi-bin/ > mailman/listinfo/time-nuts > > and follow the instructions there. > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/ > mailman/listinfo/time-nuts > and follow the instructions there. >