The 6BM8 is an audio triode plus output pentode of seven Watt anode dissipation. The output section 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 triode on the left is screened from the power valve on the right. The pentode has radiating fins on the copper supports of the control grid.
A detailed view of the construction. The vertical strips near the base connect the heater pins to the two sections. The pentode cathode has a rectangular cross section.
The triode anode with side flanges for extra cooling area.
The pentode anode. The bright work on the top connects to g3, the cathode and the screen.
The thin glass tube envelope is 20 mm in diameter and excluding the B9A base pins the valve is 71 mm tall.
References: Data-sheet & 1040. Type 6BM8 was first introduced in 1956. See also1956 adverts.
