The U301 is an efficiency diode for television line scan. In use it returns energy from the collapsing magnetic field in the line coils during flyback into to the HT rail and hence to the reservoir capacitor.
The peak inverse voltage is 4,500 Volts, the peak anode current is 600 mA with a maximum rectified current of 120 mA. The heater needs very good insulation in these rectifiers and for the U301 the maximum heater - cathode voltage is 4500 Volts.
The U301 has a 200 mA heater and the U191 has the same ratings but has a 300 mA heater.
This exhibit has lost the main identification. All we have are the details scratched on the base cap.
The broad part of the anode. Note the base of the cathode tube.
The top mica like the Ediswan U301 the separation of heater from cathode is by a ceramic tube. Unlike the Mazda U301 that uses an insulated helix.
Microscope image of the lower mica showing the ceramic spacer tube.
The top mica shows the cathode connection to the top cap and the ceramic spacer tube that provides the extra heater/cathode insulation.
The wide glass tube envelope is 29 mm in diameter and, excluding the IO base pins, is 88 mm tall.
References: Data-sheet, 3002 & 1040. Type U301 was first introduced in 1953. See also1953 adverts.
