kb8tq@n1k.org said:

Could you please say more...

Does that mean unplugging gear with always-on OCXOs?  Or dumping the main
power to the lab when the lights are turned off?

--
These are my opinions.  I hate spam.

Hi

Ok, well since I was asked to say more :)

Long ago heavy users of this sort of gear figured out that you wanted to keep the OCXO’s on
all the time. That was the way  to make the gear the most stable. That is the way you
can use your counter / generator / whatever  when you get to work in the morning. A house
standard is not always the way labs are wired.

Over the years this power on approach ran up against facilities groups that had objectives to reduce
building costs. As the costs went down, their bonus went up. A multitude of reasons thus
were generated as to why it was a “really good idea” to turn everything off at night / at lunch/
in odd numbered hours. Most of them were pretty easy to fight. The “fire hazard” one was
a bit harder to address. It became a conversation point in buying gear.

Conversation points tend to flow into odd specification details. They may or may not show
up in the written specifications. They are there none the less. The fuse in the 10811 is there
because of fire / smoke hazard concerns. Is it provable that there a direct link from the
customer “concerns” to the fuse? Without full access to every memo and conversation
within HP, it can’t be proven. Based on what people have said over the years, it is the case.

Ultimately it all came to no good. The energy conservation rules simply took over. Shutting
down everything during off hours became the way a lot of outfits did things. Don’t turn off all
your bench gear and you get a nasty note. I am not aware of full power being dropped during
off hours. That tends to take out things you really do not want to shut down (fire sensors …).

I tend to pick on the US government in the context of gear shutdown. They certainly had all
these issues. The guys from the various labs certainly fought all these battles. The government is
far from the only organization that went through all of this between the late 1960’s and today.
I’m also not claiming that energy conservation is a bad idea. It comes to mind every month
when I get the electric bill ….

Bob

Hi

All of which would have required a OCXO designed to work that way. If you ever come across one, post pictures.

Bob

On 5/11/2017 4:25 AM, Bob kb8tq wrote:

A couple of comments on this, probably no surprise to many
time nuts.  All or most HP instruments with 10811's keep the
oven energized even if the instrument is turned "off".
Many classic HP instruments used power transformers for
power supplies.  The secondaries were regulated by a
combination of switches and linear regulators.  The
power module was mounted on the rear panel, along
with the transformer, to help get rid of the heat without
heating up the box too much.  The dilemma was that you
had to choose between four bad alternatives:

1. Put the power switch on the rear panel.  This is
   inconvenient for the user, especially if the unit is
   racked.

2. Put the power switch on the front panel.  This
   entails running wiring with all the safety approvals
   up to the front panel and back to the rear panel.
   I don't know of this ever being done at HP.

3. Have a button on the front panel that actuates
   a long plastic shaft the goes to the real switch at
   the back.  Works, but quite a hassle.

4. What was usually done:  leave the power transformer
   primary connected all the time and switch the secondaries.

The HP transformer shop would often scrimp on the amount
of iron in the transformer, which would increase the
core loss.  Their idea of good engineering practice was
to allow the loss to heat the transformer up 10's of
degrees.  Note that core loss is independent of how
much power you are drawing from the secondaries, if any.

So in the overall scheme of things, the 10811 is small
potatoes.  Once it is warmed up, it doesn't draw much
power.

Rick N6RK