[time-nuts] HP 5061Bs on ebay

[cdelect at juno.com]

OK these are my personal opinions, remember buying a used cesium standard
is allways problematic.
If the vendor can give you a few readings like actual EM voltage, SN
ratio. and an ADEV plot you can have a bit less concern. However vendors
are unlikely to do that!
If I was going to buy one I'd only get one if it had the later model
"mini" tube and the tube was a standard tube.
Item 404305639849 on eBay does indeed have a standard mini tube as seen
in the PIX. (mini tubes have the black spacers to build the tube up to
the diameter of the old tubes.)
It is interesting to note that as far as I can tell the only difference
between the mini tube for the 5061 units and the tube in the 5071A is the
connector pinouts. (although the 5071A tube has an EEPROM in one of the
connector shells.)  I have in the past installed a mini tube into the
5071A with good results. I suspect that when the government still wanted
tube replacements for the 5061 units that rather than having two tube
manufacturing lines  HP just decided to eliminate the old tube line and
make 5071A tubes with modified connections for the 5061A/B.
So a mini standard tube being the last ones built for the 5061A/B might
have less time on them giving you a better chance at a good usable tube.

Good Luck!

Cheers, 

Corby Dawson