The 6F33 pentode has two open anode plates one each side of the central electrode assembly. The wire grids are rounded at the gaps in the anode and flat between the anode sheets. The suppressor grid is close to the anode with the screen grid close in to the cathode assembly.
Ray Cooper has supplied the following additional information. The 6F33 was a special purpose valve and has an unusual suppressor grid arrangement. In fact the valve was specially deigned to have an exceedingly short suppressor grid base, meaning that the valve could be easily cut-off by applying a negative bias to the suppressor. It is believed that approximately 10 Volts was all that was required for full cut-off. It is also probable that this valve features an internal diode to prevent g3 from being driven too far positive.
The 6F33 behaved extremely well in Miller-Transitron timebase generators, in which the suppressor grid (g3) was used as a control electrode. This was confirmed from Ray's own first hand experience of designing such circuits.
Here the close wound suppressor grid is seen from the supports. The two anode plates joined by a strap can also be clearly seen. The suppressor grid pitch looks to be close to that of the screen grid. The control grid is not visible.
There is screening above and below the mica discs. The copper control grid supports are topped by a heat radiating fin. The mica discs are doubled-up to provide vibration resistance.
The reverse carries the CV designation CV2209 together with KB/F. The KB/F identifies this valve as being made to specification K1001 or K1006, the B denotes qualification by a UK authority and the F identifies the maker as STC, Paignton.
The thin glass tube envelope is 18 mm diameter and excluding the B7G base pins, is 45 mm tall.
References: Data-sheet, 1040 & Ray Cooper. Type 6F33 was first introduced in 1949. See also1949 adverts.
