Monsanto 101B frequency counter (1969)

The Monsanto 101B is a compact frequency counter-timer. It comes in a metal case with a tilt stand for bench use. Its display has five Burroughs B-5750 nixies and uses TTL IC's for the digital circuitry.

The 101B has a number of rotary switches to select the operating mode and gate time. It is a nice and compact counter, not too large like some other nixie frequency counters I have.

I bought this counter in spring 2004 through Internet. The person who sold it was a radio amateur who didn't use the counter any more. He didn't know whether it still functioned.

When I tried it, counter did work, but the range switches seemed to be a bit unreliable and the readings were not exact.

Initial repairs

The counter was pretty easy to fix. Cleaning the switches and some of IC sockets made this counter work again. I have been using it for years when my FC7008 frequency counter had to warm up. It proved to be easy to use but it has a limited precision, which is not a problem in most cases.

Adding an on/off switch

The original on/off switch is a switch integrated with the display time control potmeter. That switch wasn't working any more. The previous owner had bridged it so the counter was On as soon as you put the plug into the mains outlet. I decided to add a miniature toggle switch so I could switch the counter on when needed while leaving the plug in the wall. This was easily done.