The type Z66 was M-OV's late-1930s in-house attempt to make a small, modern high-slope pentode for wide-bandwidth IF systems in TV and radar, where bandwidths of several MHz were required.
This is an earlier example than our other Z66's as it has the metal skirt and not the composition base.
To ensure that the valve would be cheap and easy to make, a 'pinch' construction was used that could be assembled on existing production line machinery. Sadly the Z66 was very much a 'second best when it came to performance, particularly in terms of gain-bandwidth product and high-frequency noise figure.
The high bandwidth receiving valve that won the War was the pinchless EF50 not the Z66, even though they had comparable data-book characteristics. The extra lead length added too much inductance.
Looking along the pinch it is clear that from pin to working electrodes is much longer than in a pinchless design such as the EF50.
The remains of the Marconi label can be seen close to the skirt. The anode plates are small compared to the area covered by the grids.
The wide glass tube envelope is 29 mm in diameter and, excluding the IO base pins, is 81 mm tall.
Reference: 1043. Type Z66 was first introduced in 1948.