Ballantine 323-7 AC RMS meter

[cncjerry]

I picked-up another A/C RMS meter A/C only) to use for receiver testing, a Ballantine 323-7.  Seems very accurate.  This like my HP 3400a uses a thermistor I believe.

It makes a buzzing sound when powered on, not that loud but noticeable.  Sounds like a transformer issue?  The other thing I noticed is that when I shut it off, I hear a high frequency squeal or squirt kind of noise, something like an old TV would do.  I realize this meter is a little different but was wondering if others have the 323 and hear the same thing before I take it apart.  Lots of screws to get the covers off.

Thanks

Jerry

[cncjerry]

By the way, I was wrong on the thermistor, it uses a square law RMS detector.  Also, I believe it has a chopper amp, maybe mechanical?  could that cause the noise?

Thanks

[Kleinstein]

I would be surprised to see a mechanical chopper amplifier.

There is a slight chance to find a DCDC converter to produce a few supply ranges from a single battery supply. This might cause the high pitch noise and maybe also some noise.

[cncjerry]

I opened it up and it uses a mechanical chopper relay, a syncroverter c1417-49.  That's what's making all the racket in there.  It runs at 94hz.  I guess it is normal. 

I had heard of people converting the mechanical to electrical in the past and am going to look around.  The meter is right on the money so I'm probably not going to change it out, just get a better understanding of it.

Thanks

[Vgkid]

Looking at the schematic you could  replace the multiple gain stages with an az opamp and cascade another opamp(or not). Pretty much keep everything forward of the chopper. Especially those cool backward tunnel diodes.
Schematic /parts below.
https://m.imgur.com/a/weYVBGj

[N3DEB]

I have this Ballantine 323-07. I only have the basic 323 manual, looking for the one that covers 323-07 and cant find Anywhere! Even contacted Ballantine. Anybody have this?

[edavid]

I have this Ballantine 323-07. I only have the basic 323 manual, looking for the one that covers 323-07 and cant find Anywhere! Even contacted Ballantine. Anybody have this?

This is not 100% complete, but should get you started.

[N3DEB]

This pdf is a big help and step forward! Many thanks!

You are correct, very useful though not complete in that it does not have the attachment for the 323-07 schematic and parts list. The previously posted schematic though marked 323-07 is not the same as my version, serial number 024-6917.

[edavid]

This pdf is a big help and step forward! Many thanks!

You are correct, very useful though not complete in that it does not have the attachment for the 323-07 schematic and parts list. The previously posted schematic though marked 323-07 is not the same as my version, serial number 024-6917.

Did you see the schematic on page 6-10?  Is that different from your unit?

[N3DEB]

I was going by the statement below in "Section 9 Backdating Information" 9-3 that states a serial number range that includes mine that references a different schematic. The one that you provided is probably very close - damn sure better than the one in the basic 323 manual that is available around the web. I am so far not into any repair to say how close it is, rather working on calibration which this manual represents very well and likely perfectly covers my unit.

If I do I will post what I find.

9-3. Attached here to are schematics and parts
lists for the following:
a. Model 323 Serial Number 2194 and lower
b. Model 323-01 Serial Number 101-2194 and
lower.
c. Model 323-06 Serial Number 101-2194 and
lower.
d. Model 323-07 Serial Number 101-2194 and
lower.
e.

[N3DEB]

Oh wait!

Looks like there are two schematics in your pdf. There is one stating 323-07, my bad.