The 6BM8 is an audio triode plus output pentode of seven Watt anode dissipation. In this exhibit the output valve is a beam tetrode rather than a pentode.

The triode section has a amplification factor of 70, and this valve was much used in record players with crystal pickups. The latter had a relatively high output and when coupled with the single ended pentode output stage made effectively a single valve design. Only a rectifier was required to complete the line-up.

The pentode section looking along the grid axis. The bright plate entering the anode forms one side of the beam plate and also connects to the screen between the triode and the pentode (beam tetrode).

The triode section with the screen between the anode and the pentode anode. Both sections have the control grids wound on copper supports and the power section has heat radiating fins on the grid support rods.

The thin glass tube envelope is 20 mm in diameter and excluding the B9A base pins the valve is 69 mm long.

References: Data-sheet & ¹⁰⁴⁰. Type 6BM8 was first introduced in 1956. See also 1956 adverts.

Pin Connections

B9A

1

2

3

4

5

6

7

8

9

g1(t)

k,g3,S

g1

h

h

a

g2

k(t)

a(t)