[time-nuts] Re: HP 5061: Unable to adjust beam current to less than 46nA

[Matt Huszagh]

Corby Dawson via time-nuts <time-nuts at lists.febo.com> writes:

> You can select a resistor to drop the EM volts down some more.
>
> This would allow you to drop the beam current.
>
> However the instrument will work just fine at your values.
>
> As long as you can adjust the loop gain on the A7 to get 40 on the 2nd
> harmonic I'd just leave it as is.
>
> I have a 5061B that has an excellent tube. The minimum E.M. is 1200V and
> my beam current is around 48 (mod on). I just use it that way as it's a
> hassle to tear into just to change the beam current indication.

Thanks for the confirmation Corby.

I can adjust the loop gain to get a 2nd harmonic reading of 40 at the
lowest beam current setting. However, I performed the loop gain
adjustment (5-220 in manual) to set the A8J1 phase detector test output
to +/- 1.6V when the fine frequency adjust is set to 200 and 300
(normally 250, where the test output is 0). After doing this, the 2nd
harmonic reading is >50. When I adjust the loop gain such that the 2nd
harmonic is at 40, the phase det test output is much less than +/-
1.6V. I suppose maybe that +/-1.6V is only applicable with a 25nA beam
current. Is that right?  Should I neglect the phase det test output
setting of 1.6V and just set the loop gain such that the 2nd harmonic
reads 40?

Matt