The Tungsram HP4101 is an RF pentode with external metallising paint, This RF pentode was made with both B7 and B5 base caps.
There are many valves with the same pin arrangement but all are slightly different in characteristics to the HP4101. Tungsram made the HP4100, HP4101 and HP4101c all with the same headline operating details - obviously subtle differences existed. The CV1879 has the HP4101 listed as sensibly equivalent but the CV specification requires the valve to withstand peak anode voltages of 1 kV and Tungsram make no such claims about this Type.
The anode end; Little detail is revealed about the valve.
The B7 base.
Thanks to Mark Mallison for sending the images.
The classic envelope is mm in diameter, and excluding the B7 base pins is mm tall.
Reference: 1043. Type HP4101 was first introduced in 1935. See also1935 adverts.