Equivalent to X78 Valve?

[Geordie McBoyne]

I think the X78 was developed at the behest of EMI for use as the mixer-oscillator in the HMV 2807, the Birmingham version of the TRF model 1807. All the valves in the 1807 RF unit were B7G types Z77 and D77 and the conversion to superhet would have entailed new chassis metalwork if a B8A or B9A frequency changer valve was to be employed.

Geordie McBoyne.