A 1968 frequency counter gets more than a cleanup in CuriousMarc’s new HP 5221B restoration video, published on 12 October 2026. The instrument began as a five-digit Nixie counter rated to 10 MHz; by the end of the project, the team says it has six digits.
That extra digit is the intriguing part of this repair. It turns a restoration of vintage test gear into a small hardware-modification story, while retaining the appeal of a working Nixie display. The 20-minute video follows the hands-on work inside the counter rather than merely showing the finished front panel.
Watch the original video on CuriousMarc’s channel for the repair and modification.
