An HP 5326B enters my lab

It was just a matter of waiting until I could buy an old/surplus/vintage HP device with Nixies for little money. Unknown conditions, of course.

I bought an HP 5326B Electronic Counter in Basaluzzo HAM flea market (June 2023) which was designed to measure 100 mV up to 50 MHz and display the result on 7x B5750 Nixies (or similar). It also has a 1000Vdc voltmeter measured using an internal V/F converter.

Display board of HP 5326B.

On a first visual inspection the unit was serviced once to replace a 1820-0119 IC that was actually rebuilt with TTL ICs! It had loose screws of the top cover, so I wasn't hoping for the best but I powered it up nevertheless.

Well, well, it sprang to life and seemed to give proper readings, so I needed to read the manual to check for proper operation and calibration check.

The unit is in proper working order. The stock 10 MHz reference oscillator is spot-on at least for the precision I can reach in my lab. The DVM might be reading 1% high my calibrated voltage source, but I'm comparing it to other uncalibrated, various era, less resolution devices.

I like the possibility to make it count events until the reset button is pressed, which means it can become a clock with very simple interfacing.

The rebuilt 1820-0119 does not implement leading-zero blanking so the 7th digit is always on. I'm even thinking of building a modern replacement of the counter+buffer pair 1820-0119/1820-0116 by means of a microprocessor. This way I regain the leading-zero blanking and I might even add the 8th digit option!

I played a little game: how far does it measure beyond the 50 MHz upper limit? I used the NanoVNA as a frequency generator using the "CW mode" (alternatively you set the Span to 0). I have no idea of the signal amplitude at this point but it reached 95.000 MHz! The counter is 9.3 kHz high (0.01% or 100 ppm).

HP 5326B measuring 95 MHz.