The X79 is a triode hexode frequency changer or mixer. The triode control grid is connected internally to the oscillator injection grid (g3) of the hexode.

The Osram brand label of the M-OV company.

The thin glass tube envelope is 21 mm in diameter, and excluding the B9A base pins is 48 mm tall.

References: Datasheet & ¹⁰⁴⁰. Type X79 was first introduced^¶ in 1950.

 
Pin Connections

B9A	1	2	3	4	5	6	7	8	9
	g2,g4	g1	k	h	h	a(h)	g1(t),g3	a(t)	ic

 
Absolute Maximum Operating Conditions^¶

Hexode	Vh	Ah	Va	Vs	Vg	mAa	mAs	ra
	6.3	0.3	250	100	0	4.5	3.4	0.7M

Thanks to Frank Philipse for supplying the above PDF datasheet