The counter can measure frequency and time and can handle up to 250 MHz. Two knobs on the front are used to set gate time and select one of 6 functions:
Most of the circuitry is mounted on a single large circuit board. This board has been made by the constructor of the counter, as it is bearing his call-sign. Looking at the quality of the board (it has tin-plated traces), I get deep respect for his skills. Electroplating a PCB, probably using the tin coating to protect the copper not to be etched away is a sophisticated way of PCB manufacturing.
This counter has a lovely nixie tube display consisting of:
The control circuit consists of 2 SN74121 monoflops, a 74S00, a 7400, a 7451 and a 7413. The counter has a 1 MHz crystal as frequency reference and a series of 7 SN7490 dividers to produce the different port times and timing frequencies.
For the 250 MHz input, a fast counter chip is used as a pre-scaler. This is probably an ECL chip, as it has a heat sink on top. It is placed on a separate pre-scaler board situated right behind the 250 MHz input below the main board.
Under the main board there is an additional PCB that holds 5 extra 7400 chips as reset circuitry for the clock function.
The power supply is using a small (25 VA) transformer, that looks like it has been custom wound. The label states it can deliver 8.5 V at 1.5A and 170 V at 50 mA. The constructor has added an extra 15 turns of wire to boost the 8.5 V secondary. The +5V is regulated by an LM305 buffered by a 2N3055 and 2N2807. The power transistor is running quite hot as does the transformer. I think the power supply may be a bit underdimensioned.
After I checked the state of the components, I switched on the counter. It just worked and showed a series of pretty zeroes. When I tried the Clock mode, that just worked. Setting the time requires some fiddling with the period selector and the start/stop buttons. I will have to recallibrate the time base and see if I can find a purpose for this neatly built DIY counter that deserves to be kept in honour.