I've been trying to restore an old HP400D Vacuum Tube Voltage Meter. Section 5-20(f) in the manual says:

Measure the direct current in the lead from V7 (pin 1) which must be less than 60mA... Excessive current indicates a short or partial short in the circuits of the voltmeter amplifier section. A clip-on type milliammeter should be used for this measurement.

Presumably, the manual is saying to use something like the HP Model 428B. Unfortunately, I don't have one. Therefore, I am wondering if there is another way to measure the DC current without having to cut the wire. Since I'm only testing for a short (or near-short), and the expected current is very small, I don't think need an extremely accurate measurement. Any ideas?

  • \$\begingroup\$ You might want to google "Hall effect sensor". But what types are available and which ones would work with whatever meter you do have, I don't know (and digging in to the specifics would make this a shopping question, off topic for this site). \$\endgroup\$
    – The Photon
    Commented Dec 29, 2016 at 18:58
  • \$\begingroup\$ The "Theory of Operation" section of the manual you linked might also give you some ideas if you want to DIY. \$\endgroup\$
    – The Photon
    Commented Dec 29, 2016 at 18:59


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