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The DA30 is essentially an uprated PX25 with a wider grid pitch and lower μ value. It was intended for use in push-pull pairs (Class AB1) to provide up to 45 W of undistorted audio for PA systems and transmitter voice modulation. In this respect it is nearly twice as powerful as the PX25.

This exhibit is also marked as POVT111 for GPO use.

The advantage of Class AB1 is that it allows very high peak output with large variable signal levels (eg. audio) but consumes relatively little power whenever the signal level is (briefly) low, as with speech). The penalty is that a large negative grid bias is required and the peak signal input must be correspondingly high. Up to 288 V pk - pk. However, as the grid circuit does not need to consume significant amounts of audio drive power, the preamplifier can be a low power type and the high peak grid voltage requirements can be met by using a push-pull drive transformer. Heavy but efficient and cool-running.

The balloon envelope is 65 mm in diameter and, excluding the B4 base pins, is 137 mm tall.

References: Data-sheet & private communication. Type DA30 was first introduced in 1935. See also 1935 adverts.

Pin Connections

Absolute Maximum Operating Conditions^¶

Thanks to Frank Philipse for supplying the above PDF datasheet.