Another piece of historic equipment: HP 400F AC Millivoltmeter

[david77]

Here's another piece of my collection of antique measurment equipment:
The HP 400F AC Millivoltmeter.



I had to open it to clean the contacts on the range switch. As you can see on the picture below
they had some severe oxidaton problems, it had gotten worse in the last few months so I decided
it was time to have a look inside the thing.



I can now date my unit to about 1973/74 from date codes on the Sprague electrolytics inside.
According to information found on the www it was in production from 1966 to about 1985 in
the US, England and Germany. Mine's got the "Made in W. Germany" label on the back.



The double sided PCB is of highest quality as you would expect from an instrument such as this.
Circuitry is completely discrete, not a single IC in sight.





The scale is calibrated to use dBm (1mW @ 600R) and as such is ideally suited for audio work.
Specified frequency range reaches up to 4MHz, fullscale error depends on frequency and selected
range, it varies between 0,5% and 2%.

The meter can be powered from 115/230V AC or from batteries.

My unit was last calibrated in 1988, at least that's what the sticker on it says. It still works fine,
even though I don't bother to have my meters calibrated. As long as they all more or less
agree with each other it's OK with me  .

[amspire]

I used to use these for Audio/Telecom work back in the early 80's.

In many ways, better for audio then digital as the meters have all the needed accuracy, and the meter is so much more responsive. You can pick up problems that are easily missed with a digital meter.

I almost bought one about 6 months ago, but with my bench space, I just wouldn't use it much.

A real HP classic.

Richard.

[seattle]

This is quite a find. I just reviewed a NatSemi data sheet (LP2975) that was revised in June 2011, and they reference measurements made on an HP400. Think about that: No telling how many pieces of equipment are in that NatSemi lab, and they report an HP400 measurement.

Thanks for the pics

[SAUL BRITTO]

I have one unit hp 400F too,but the pointer of vu, hits the final of scale very strong,i dont now why dont crash! It do that when on or of,can you help me?