[time-nuts] DC heater in older HP5061A?

[Hans Agema]

Hi all,

After lurking below sea level in Amsterdam, allow me to surface with a 
specific question...
In short, I am a typical Electronics Engineer with too much curiosity in 
too many subjects and a
chronic shortage of time.... Metrology is one of my fascinations, ranging 
from a solid invar standard
meter (salvaged from the skip at work) to a still aging HP106B and a Z3816.

Right now I managed to get a 1971 HP5061A (ser. 1124A00503) up and running.
I recently bought it from Robert Deliën, who in turn had obtained it 
shortly before from Erik Kroon,
both subscribers to the list too.
The instrument originated from the Dutch Standards Bureau and contained 
what appears to be the
2nd tube in its life span (ser.nr 1749 of series 1240A), judging by the 
notes on the operating record.
Robert had already repaired the HV power supplies and oven controller, but 
lacked the time to finish the job.
To cut a long story short, after a day I had it in operating mode and 
locked, but after a few hours
the control voltage wandered off again.
It boiled down to a tin whisker on one of the intermediate pcb's inside the 
5 MHz OCXO (00105-6013).
It shorted the -EFC voltage when fully warmed up and cost me several hours 
of sleep and a couple of
days to locate it and repair the darn thing.
Probably this fault was the reason for decommisioning the 5061A, as the 
tube shows a healthy beam current
at low temp.

Now it is rock steady whining away in more or less constant phase shift to 
a 58533A at work.
Next step would be killing that 2 KHz whine by supplying 5 volt DC (through 
a PID controller with SS switch
at a 1 second cycle time) to the heater.
This particular tube has a type T thermocouple built in, very handy to 
check the Cs oven's exact temp and to control it.

Hence my questions:
Will heating the Cs oven with DC have any influence on the C field?

Can anybody provide me with, or point me to, the 5061/5062 circuit of the 
later DC heater?
I have the pdf''s for the first series up to 1740A prefix.

The 2 kHz inverter powers the ionizer wire, the heater and the original 
neon choppers in the opamp module.
Taking out all but the ionizer will drastically reduce the audible noise. I 
can imagine that feeding the ionizer
with DC would disturb the EM entry focussing, so I'll leave that in for now.
I remember reading somewhere down the list that High Performance tubes ran 
exclusively on DC.
A second "donor" unit I have, has a HP tube (#1908A00865) that still shows 
the tap settings for the AC controller.
Haven't checked that tube yet, it has a history in the German FTZ.

Thanks in advance for the trouble of answering my question,

73, Hans PA0LED