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HP 456A ??

Discussion in 'Electronic Equipment' started by Henry Kolesnik, Feb 15, 2004.

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  1. I just got this HP 456A AC Current Probe and need some help to get it going.
    The 1977 HP catalog indicates that it could operate 400 hours on batteries,
    not very long for what's in it. The dead batteries that came with it are
    Mallory TR 236R at 8.1 volts and TR 234R at 5.4 volts, these are C size
    diameter. There are only two 2N5087 transistors, a diode, and a few
    resistors and capacitors in the circuit, what's the current draw? I am not
    sure that these are the correct batteries but would like to know if anyone
    out there can be confirm the batteries or has a schematic, manual or AC
    power supply. If I can't find an HP optional AC supply I think I'll build
    a little Zener stabilized supply after I get the voltages confimred.
    Hank WD5JFR
  2. Hank,

    According to my 1967 HP catalog (in surprisingly good
    condtion, by the way) the 456A uses two TR233R's and one
    TR234. It does not list current required (and I guess
    the 1977 catalog does'nt either.)

    My catalog also estimates battery life at 400 hours.

    You might search the net for mercury battery current
    capacity. I seem to recall it is somewhat less than
    nicads, but I don't remember the ratios.


    Phil - N4GWV
  3. Thanks to David DiGiacomo I've got the info and it looks like the B+ is 5.4
    VDC at 5.5 ma and the B- is 8.1 VDC at 20 microamps! HP used a small
    centrer tapped transformer at about 25 volts that was regultaed down to the
    8.1 and 5.4. I can't find anything on the physical size of the xfrmr but it
    has to be no bigger than end of ones thumb,but maybe they used a wall wart
    but I kind of doubt it. I've not had any experience with real small low
    current xfmrs that take 115VAC to 20 or 30 VAC and would appreciated any
    ideas on what to use. A wall wart would be my last resort.
    hank wd5jfr
  4. Neil S.

    Neil S. Guest

    FWIW, Henry, I prefer to use an AC output 'wall wart' and install in
    the unit to be powered a pair of diodes to supply + and - which I
    filter and regulate down to what is needed. For that miniscule power
    demand the filter caps and TO-92 regulators will take up little room.

    Neil S.
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