[time-nuts] New Guy, has HP 5061A with DATUM 7105A tube seeks advice

Pete Lancashire pete at petelancashire.com
Thu Nov 6 12:54:55 EST 2014

If after say a week and the current does not go down, there is one more
thing you can do before you have a tube that qualifies as a door stop. You
replace the internal HV supply with 3,500V @ 5 mA I had to do this on mine.
Keep doing it a few minutes at a time, took something like 3 hours.
No drop in current until the very end and all of a sudden the current
starting going down. I put the tube back in the 5061A and after the current
dropped there was enough Cs left to get the thing to work. Just like Paul
I'm sure there is very little left.

I turn it on every 3-4 months and let it run for about an hour. The last
few times it took a while to lock and go 'green'


On Wed, Nov 5, 2014 at 11:21 PM, Wayne Holder <wayne.holder at gmail.com>

> I recently picked up a 5061A surplus, but have no idea whether it works or
> not.  The first hurdle is getting a power cord, but I'm still waiting for
> the proper connector to show up (the first one I ordered had the wrong
> orientation on the 3 pins.)  In the meantime, I've been reading though what
> materials I can find online in order to figure out how to  try and safely
> turn it on and see if the tube is OK, or dead.
> However after removing the top cover, I can see that my unit doesn't seem
> to contain the typical kind of cesium tube assembly I see in the HP docs
> I've found online.  Instead, it has a tube made by DATUM with the following
> markings on the label:
> Model: 7105A
> Serial: 9951991226
> Part No: 03667-501
> Oven Temp: 92 degrees C
> Oven Monitor Therm: 101 Ohms
> EMV: 2000 DC
> NSN ______ 5960 01214 7475
> Can anyone tell me about this model and why it might have a DATUM tube
> rather than the kind I see in the HP oc?  Also, any advice on how to safely
> check it out?
> I bought this thing out of curiosity but, upon looking inside at all the
> various dials and switches and multi-turn potentiometers, I find I'm rather
> intimated by it, even though I have a fairly decent background in
> electronics.
> Wayne
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