[time-nuts] 5061A Beam Current question
J. L. Trantham
jltran at att.net
Tue Dec 11 13:46:36 UTC 2012
There are two HV power supplies, +3500 (A18) and -2500 (A19), both of which
can 'sing'. A18 comes on when power is applied and in CS OFF mode. A19
comes on when you move to any mode other than CS OFF. There is also a
battery back up option, Option 002, that has a battery charger board (A2),
that can sing when trying to charge 'dead' NiCd's. It comes on when power
is applied and in CS OFF mode as well. A2 can be removed with no effect on
the rest of the unit to test that theory. When does your unit start
The BEAM I indication can be adjusted by the BEAM I METER pot on the control
panel. It only adjusts the meter indication, not the beam current. The
beam current can be affected/changed by the C FIELD adjustment and by
following the instructions in the manual to align the oven controller (A11)
and the Electron Multiplier on the Power Regulator board (A15). Once
aligned, adjust the BEAM I METER pot for an 'on scale' indication. This is
different on the 5061B where BEAM I METER on the control panel is replaced
by BEAM I and is, in fact, the Electron Multiplier adjustment. There are
different versions of the A15 board, some of which have a pot to adjust the
electron multiplier and others with fixed resistors.
The change in BEAM I indication as you adjust the COARSE freq can be very
small. The larger the beam current, the greater the fluctuation, but it can
still be very small, a division or two. The figures in the manual are quite
'magnified' in my experience. However, I have never played with a 'new' CS
The change in BEAM I indication as you adjust the COARSE freq is also very
easy to miss and it takes only a very small adjustment of COARSE to go
through the entire range. My usual procedure is to let the 5061A warm up
for several hours, in the CS OFF mode, make sure the OCXO is stable, then
compare it's frequency to that of a GPSDO, then adjust the COARSE freq (with
FINE set to 250) to precisely match the GPSDO. I have a TBolt that I use
it's 10 MHz to trigger the horizontal of a scope and put the 5 MHz of the
5061A to the vertical. That done, I then select LOOP OPEN, let the CS oven
warm up, the BEAM I come up, the 2nd HARMONIC come up, then select CONT OPER
and hit the RESET button. If the OCXO is 'on frequency', CONTROL should
indicate zero and you should be on the top of the center peak. Adjustment
of the COARSE should then be able to demonstrate the 'peaks' to prove you
are on the top of the center peak.
I don't recall any 'false' modes that will give an erroneous indication.
However, I have had failures in the LOGIC board (A14) that have caused
These units are fun to play with and work on. They make great 'house
standards'. I leave them in CS OFF all the time, which lets the OCXO and
ion pump run continuously.
Hope this helps.
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Pete Lancashire
Sent: Monday, December 10, 2012 10:59 PM
To: Discussion of precise time and frequency measurement
Subject: [time-nuts] 5061A Beam Current question
I've got a couple questions on a early S/N 5061A I got a few days ago.
It took a couple days but the Ion Pump current is now down to "zero" or at
least less then one division on the meter.
I'm able to get the unit to go into continuous operation mode by following
the TURN-ON PROCEDURES but have a few qestions
1. The unit 'sings' I'm tone deaf but its a high pitch. It could take some
doing to isolate where it is coming from. Any ideas ?
2. How much should the beam current change when turning the OSC FREQUENCY
COARSE adjustment ?
On time about 45 to 60 minutes
The current scribbled on the door is 19, I'm running pretty much 30. When
making the adjustment the difference between the peak and any other position
is only plus/minus a max of 2 or 3.
3 And i guess for last, are there any false modes that will turn off the
ALARM and turn on the Con't Operation light ?
PS Anyone have a side panel without the front handle broken ?
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