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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.

The suppressor grid and its close wound style can be clearly seen. Most suppressor grids are very open wound.

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.

See also s6F33 for the special quality version and an excellent view of the suppressor grid.

The thin glass tube envelope is 18 mm diameter and excluding the B7G base pins, is 46 mm tall.

References: Data-sheet, ¹⁰⁴⁰ & Ray Cooper. Type 6F33 was first introduced in 1949. See also 1949 adverts.

Pin Connections

Absolute Maximum Operating Conditions^¶

Thanks to Frank Philipse for supplying the above PDF datasheet.