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The VP4 is a variable μ RF pentode that was introduced in 1933 on the B5 base. A year later the B7 base version was introduced.

The gain is controlled by altering the bias on the control grid, normal operation is with the bias ranging from -2 to -22 Volts. In a superhet receiver this variation would be derived from the rectified voltage at the end of the IF chain (AGC). The stronger the signal the greater the rectified voltage and this the more negative the control grid is driven and that in turn reduces the amplification of the VP4 in the IF stage.

Both images have been sent by Mike and this shows a VP4 minus the external metallisation paint. The mesh anode and suppressor grid can easily be seen, the screen grid is just visible.

The classic envelope is 50 mm in diameter, and excluding the base pins is 122 mm tall.

References: Data-sheet & ¹⁰⁴³. Type VP4 was first introduced in 1933. See also 1933 adverts.

Pin Connections

Absolute Maximum Operating Conditions^¶

Thanks to Andy Cowley for supplying the above PDF datasheet.