The Cossor 240B is a double triode AF output valve designed for quiescent push-pull use in battery receivers. The 240B was introduced in 1934 as was the Mullard QP21. Other quiescent push-pull valves in the museum are the triode PM2B and the QP230 double pentode from Mazda plus the QP22B from Mullard.

This type of operation with very little standing anode current is known as Class B. and the 240B required up to 40 Volts peak to peak grid to grid input signal.

Cossor in the leaflet that came with this 'new' valve recommends the Cossor 215P as a driver. To drive the 240B

The envelope is mainly covered with the silvery deposit of the Magnesium getter material but from the rear the twin box electrode systems can be seen.

When seen close-up and from the top the grid can be seen through the top mica support.

The balloon envelope is 47 mm in diameter, and excluding the B7 base pins, is 90 mm tall.

 
Pin Connections

B7	1	2	3	4	5	6	7
	g1(2)	g1(1)	a(1)	f	f	-	a(2)

 
Absolute Maximum Operating Conditions

Triode	Vh	Ah	Va	Vg	mAa	Pout
	2.0	0.2	120	0	3.0	2.0W Ra-a_8,000

Thanks to Frank Philipse for supplying the above datasheet

This exhibit was last updated on 02 December 2007 {find valves by name}