In this installment of the tube of the month series I'm going to present a directly heated tube. Not the usual triodes like 45, 2A3, 801A, etc, but I will start with a tube which can be regarded as an insider tip, the 46.
The 46 is not a 'real' triode but a dual grid power amplifier tube, not to be confused with tetrodes. This is maybe a reason why this tube is still overlooked and not as expensive as for example the 45. The typical audiophile is shyed away by the fact that it is not a real triode.
Plate resistance is a bit higher compared to the 45, it draws a bit more filament current and will result in slightly less output power. It will drop into most circuits designed around the 45 by changing the socket. Just make sure that the filament transformer can supply the current the 46 needs. Op points can be kept the same as long as the plate voltage stays below the limit of 250V for the 46. The tube has a larger bottle than the 45, same size as a 2A3.
I have a 46 single ended amplifier in the making which I will present soon. Stay tuned!