Manufacturer:  Hewlett-Packard Model:  524B Year:  1957 Schematic:  RE

Max. Rate:  10 MHz Display:  1-of-10 neon, analog meters Digits:  8 Logic:  tube

The HP524 was a remarkable instrument in it's day with it's high count rate. This is the 'B' version. It utilises 84 vacuum tubes, physically is approximately a cube of 19-inch rack-width (~ 4 cubic feet), weighs in at 110 to 120 pounds and consumes 600 watts of power. In the 1950s this is what was required to count to just 10MHz!

The photo shows the unit displaying a count of "647852.84".

While this particular unit required days of cleaning after I received it, it had remarkably little wrong with it electronically. One tube, two capacitors and one resistor solved the electronic problems.

Note: To adjust units- and tens-digit meters: with MODE=MANUAL GATE, PERIOD UNIT=100KC, GATE=OPEN, adjust CENTER pots for both meters to bring needle to dot between 4 & 5. Set GATE=CLOSED, press RESET, now adjust ZERO pots.

Note: Fan must be operating when chassis is in cabinet. If not, thermal cutout may trip after a few minutes.

For more about the 524 models see the HP 520 Series.

The 524B with a later-model (different panel colour) 526B Time-Interval plug-in plugged in. The 524B was counting during the exposure of this photograph. Note the digit which has progressed from 7 thru 0 to 1, with the consequent carry incrementing the next digit from 2 to 3 (click photo for larger view).

Top view showing AC-4 counter string. The meter for the Tens digit is visible in the upper-left corner, along with pots for centering and zeroing the Units- and Tens-digit meters.

Rear deck: Power Supply on the right and Timebase on the left.

Right-side deck: Units & Tens Counters.

This is essentially the circuitry of the HP 520A Nuclear Scaler, the model which started the 520 Series. This also gives an idea of the complexity required to get the first decade to count at 10Mhz.

Bottom deck: Gate and Control.

Note the two massive power supply transformers at the bottom.