[time-nuts] hp5061a/b no I beam current

John Miles jmiles at pop.net
Mon Oct 19 22:23:37 UTC 2009

> -----Original Message-----
> From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com]On
> Behalf Of paul swed
> Sent: Monday, October 19, 2009 6:48 AM
> To: Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] hp5061a/b no I beam current
> John,
>     Thanks and thanks for your comments on your experiance.
> Yes the readings look good. Oven is at the temp it should be according to
> the notes.
> I do see the ionizer dc offset was maxed at 15v or so. That seemed odd.
> Does look like about 1 v diff on the ionizer. Whats the
> resistance supposed
> to be roughly 1-2 ohms???
> I noted that if I increased the multiplier voltage quite high I
> actually saw
> a bit of I but it does not happen all the time and I do not want to keep
> doing that.
> Also another strange note the multiplier voltage was supposed to
> be at -2083
> yet it was set to -1606.
> Lastly the vac is 0 it had bee about 50+ but seemed to pump down.
> But 0 seems way to good to be true.
> Thanks again

The ionizer filament is OK, with 1-2 ohms.  Its supply is OK at ~1 volt, and
the zero vacuum reading is not a concern -- it just means what it says, the
vacuum is that good.  The Datum tube in my 5061A reads very close to zero
ion-pump current, and its mass-spec voltage also wants to be set near the
maximum end of the range.

But the weird EM voltage doesn't make much sense.  Either there is something
wrong with the main supply or the ground reference for it (how's the ripple
look?  any open filter capacitors?), or someone else was playing with it in
an attempt to get the tube working, and they cranked the control back to
minimum when they gave up.  I'd lean towards the latter explanation, for
better or worse.

One other thing you could check is the Cs oven temp.  After running it for a
few minutes, power it down and compare the resistance across the thermistor
leads to what's printed on the tube label.

-- john, KE5FX

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