[time-nuts] Further Observation On My 5061B

[wje]

Just a nitpick - the reading on the meter isn't any particular scale, 
it's essentially arbitrary.
The actual beam current is typically in the picoamp range. My measured 
beam current is only about 400 pA.

I'm not sure what you would be seeing from induction; the beam current 
is a result of current flow from the electron multiplier, which is 
stimulated by electrons from the ionized cesium. There are no inductive 
components, and in any case the frequency of the degaussing is so low 
(0.2 Hz) that any inductive coupling would be extremely low.

My guess would be that you actually have an at-least marginally working 
tube, but have a failure in your synthesizer, or in the microwave 
generator. Have you done the harmonic generator alignment in the manual? 
I don't remember if you said if you did the LF test, that's a good 
diagnostic also. If you have a high impedance voltmeter, (100 megs), you 
can directly measure the beam current following the procedure in the 
manual. This will eliminate any problems in the amps and detector. Go to 
open-loop, mod-off, monitor the current and very slowly adjust the 
coarse 10Mhz. You should see variation at resonance peaks.

BTW, even when operating correctly, you have to be quite precise when 
doing the coarse frequency adjustment; the peaks are very narrow and 
easy to miss.

One final thing you can do is to go to open-loop, mod-on, amplifier gain 
switch to high and crank the gain up as far as you can, but not to 
exceed a second-harmonic reading of 40. Then, slowly adjust the 10Mhz 
coarse control and see if the second-harmonic moves anywhere over the 
control range. If you get a signal, back off on the gain and keep 
tweaking the osc to maximize the second harmonic. If you can do this, 
you are getting a beam signal, and if you can get a second-harmonic 
reading of at least 30, you should be able to get lock, assuming your 
synthesizer is working. It's also easy to end up on a secondary peak, in 
which case you will get good readings but no lock. I always adjust past 
the first peak I see to look for a secondary. If I don't find it, I know 
I was on a secondary originally and scan back to maximize the beam 
current. Again, there's not a huge difference between primary and 
secondary peaks, so you have to pay attention.

Bill Ezell
----------
They said 'Windows or better'
so I used Linux.



Jeffrey Okamitsu wrote:
> Also, the magnitude of the "bump" decreased over time, with is consistent with the way the degausser works - the current pulse decreases exponentially with time.
>  
> Jeff
>
> Jeffrey K. Okamitsu, PhD, MBA
> +1-609-638-5402
>
> --- On Mon, 10/6/08, Jeffrey Okamitsu <w3kl at w3kl.com> wrote:
>
> From: Jeffrey Okamitsu <w3kl at w3kl.com>
> Subject: [time-nuts] Further Observation On My 5061B
> To: time-nuts at febo.com
> Date: Monday, October 6, 2008, 1:03 PM
>
> I forgot to mention in my email yesterday that when I did a degaussing procedure
> (using the 10638A) the Beam current peaked above 20 nA during the early part of
> the procedure.
>  
> At first, I took this an evidence that more beam current could be obtained -
> that is, the mass spec system needed to be tuned.  However, upon further
> thought I suspect that what I was seeing was inductive pickup by the beam
> current measuring system.
>  
> Anyone care to speculate?
>  
> Jeff
>
> Jeffrey K. Okamitsu, PhD, MBA
> +1-609-638-5402
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