The Cossor 6V4 is quoted as equivalent to the Mullard EZ80 but the latter is rated at 90 mA rectified current. So if run close to maximum ratings the EZ80 cannot be replaced by the 6V4.

To protect the cathode the minimum series resistance needs to be 150 Ohms.

The X arrangement of the anodes can be seen as can the fact that one anode encloses the top of the cathode while the other surrounds the lower part of the cathode. The white cylinder in the centre shows the central oxide coated cathode tube.

Although not affecting the valve's performance the Cossor lettering shows attention to detail and has considerable style.

The thin glass tube envelope is 20 mm in diameter and, excluding the B9A base pins, is 57 mm tall.

References: Datasheet & ¹⁰⁴⁰. Type 6V4 was first introduced^¶ in 1954.

 
Pin Connections

B9A	1	2	3	4	5	6	7	8	9
	a(2)	ic	k	h	h	ic	a(1)	ic	ic

 
Absolute Maximum Operating Conditions^¶

Rectifier	Vh	Ah	Va	mAa
	6.3	0.6	325	70

Thanks to Frank Philipse for supplying the above PDF datasheet

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