HP 3410A AC Microvoltmeter Anyone familiar with it?

[robrenz]

I just discovered this and picked one up but its not delivered yet.  This looks like the ducks guts for low level AC measurements.  Its lowest scale is 3µV full scale and 50nV per division.  Max is 3V full scale. I bought it mainly to do power supply ripple measurements and to characterize the below spec AC performance of my 8846A.  I know this is average responding and not true rms but it should still be very useable. This is a phase locking voltmeter with a tunable frequency range from 5Hz to 600kHz.

Anyone familiar or have some input?

Manual

Hp journal article about it   (takes a while to load and it is the second article) Edit: even more useful than I thought at first.

[poodyp]

Beauty. Have you torn it apart and given it the full run down yet?

[JuiceKing]

I saw that one, and I'm glad it ended up in friendly hands! Can't wait to see what it looks like after you give it one of your miracle makeovers.

That could be very useful as detector for a bridge. You could also use it to measure harmonics.

[robrenz]

I just won the auction yesterday and I got the shipment notification today.  I was told it does power on but they don't know if it is functional. Probably an honest answer since this was a general surplus seller not someone who knows electronic instruments.  It will get the full restore treatment and I will post the usual before and after pics.  This will be more of a challenge since the actual meter face is peeling around the edges.  It can only stand up to 100V input so lets hope nobody was probing the mains with it.

[JuiceKing]

If you want to use it as a detector, be aware that there are two very nice examples of old General Radio bridges on eBay which need them: the 1603A and 1632A. I've no doubt you would enjoy them, and they would be another kind of restoration challenge. The two on eBay now are in good condition but priced high enough that you can take your time...

[robrenz]

Another one from the same seller but this has the optional decibel scale on top meter.  Meter face is in worse condition than the one I got.

EDIT:  Sold for $15.50  ($0.50 more than my max bid )

[robrenz]

Arrived today undamaged, I warned the seller to package well if he wanted positive feedback.  It does work but it is even crustier than the picture implies.  Has some substantial corrosion of the aluminum side frames. I fed a 1mVrms sine wave at 6kHz from my FG and it tuned to the 6kHz and read approximately 1mV.  Range indicator is not working and the voltage range switch is glitchy and needs severe cleaning.

[uoficowboy]

Arrived today undamaged, I warned the seller to package well if he wanted positive feedback.  It does work but it is even crustier than the picture implies.  Has some substantial corrosion of the aluminum side frames. I fed a 1mVrms sine wave at 6kHz from my FG and it tuned to the 6kHz and read approximately 1mV.  Range indicator is not working and the voltage range switch is glitchy and needs severe cleaning.

I've seen two types of rotary switches on HP devices from this era. One style, which seems to be more common, has completely exposed contacts and is definitely cleanable. The other kind has plastic covering everything. And I have not found a way to remove that plastic. Maybe it is removable - but I did not see a means of doing so. That style seems much, much harder to clean.

It looks like the range rotary switch is not PCB mounted, so that's good. The schematics ( http://bee.mif.pg.gda.pl/ciasteczkowypotwor/HP/3410aa.pdf ) are pretty hard to read though, so I may be mistaken.

[SArepairman]

why don't you get a thermal rms meter instead?

[robrenz]

Thanks for the idea, had never looked for one.  The Fluke 8506A looks interesting but it only goes to 1µV and does not have a tuneable filter frequency. They seem to be running around $350.00, I only spent $55.00 including shipping on this.  The 3V to 3µV full scale ranges of this are perfect for my intended use. (I bought it mainly to do power supply ripple measurements <= 40µV rms and to characterize the below spec AC performance of my 8846A.)

[grenert]

Yes, I don't think anything else goes that low, or is tunable.
The classic HP AC voltmeters 400 series and 3400A go to a minimum of 100uV full scale.
Maybe something modern and expensive could go to 3uV, but you'd be way out of the $55 dollar range!
Nice find!

[robrenz]

From my dim perspective this is a manually tuneable spectrum analyzer that will lock onto and track a slowly changing frequency over a very short bandwidth (each freq. range). But it outputs a square wave at the tracked frequency and also the meter amplitude so you could graph a spectrum.  The frequency output can be used as a trigger filter for scope sync to enable triggering on a very small (specific frequency) signal in much noise, or just fed to a counter for more accurate frequency measurement.

Selective voltmeters with sweep seem to be the next step up and can go to even lower values like 0.1µV full scale.  But the 50nV/div of the 3410A is more than enough for my needs

The HP journal article shows some of the versatile uses of this meter

[uoficowboy]

Just curious - were you ever able to get this device operational?

[robrenz]

I have a few projects to get done first (to make a living) then I will probably do a video on its restoration/calibration.