[turretslug]

That's an interesting and very straightforward approach- and putting RF filtering beyond the cathode follower, so to speak, would certainly help with the criteria re. AC and DC loading. The likes of the 6C4/EC90 with small envelope and 0.15A heater loading would look to be useful here- but to manufacturers conscious of minimising expense, the time-honoured detector arrangement on its own was obviously "good enough" for the money.

Also implicit in the use of a separate triode from the accustomed double-diode-triode common cathode set-up is the need for a detector/AVC rectifier- the 6AL5/EB91 is obvious here, and double diode with separated cathodes would also allow detector and AVC circuits to be optimised for their particular desired minimum distortion or delay characteristics. Again, however, we're running up against the practical need to minimise costs...