AUDIO VALVES: 80 4274A CV617 RECTIFIER AS USED IN NATIONAL HRO DOGHOUSE PSU

Purported to be the first mass-produced rectifier to use oxide-coated tape filaments the type 80 really is a landmark rectifier.  Introduced in 1935, the 80 was the valve of choice for UX4 medium output FW rectifier valves used by the R106 HRO in the doghouse power supply.  

The 80 will tolerate a maximum reservoir capacitor of 32 µF with a minimum series resistance, to limit current of 30 Ohms.  What do you get when you replace the tape filament with an indirectly heated heater - cathode assembly, well, a slower start 80 also termed the the 80S.