TTLDFM-1 - It is a pure Transistor-Transistor-Logic-Digital-Frequency-Meter.

Uses 6 beautiful Russian IN-12B NIXIE tubes bought on ebay for less than 20USD at the time.

The project is based on David Knight's (G3YNH)  Digital Frequency Readout for Single-Conversion Short-Wave Radio Receivers.

Only minor modifications to adapt to the components I had in hand at that time.

It does not uses 74141 as the nixie driver, because I had difficulty to find them at the time I was making the PCB drawing. Now it is easy to find them on Ebay for a cheap price, if you don't mind to use Russian ICs. (I don't mind at all, anyway). But instead of the 74141, I used a standard HEF4028, and MPSA42 (only 60 of them....) to drive the NIXIES.