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R20

Sensibly equivalent to:
2J2 KY80 U26 U49
    
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The R20 is the Brimar implementation of this standard EHT rectifier. Mullard call it the KY80 and Mazda call it the U26.
The R20 is a purpose designed EHT rectifier for monochrome television picture tube supplies. It would be fed from an EHT overwind on the line output transformer and not a sine wave input. The valve is specified for a peak inverse voltage of 23,500 Volts. With a spike voltage input this suggests 17 - 18 kV for the picture tube. Normal 15 - 17 inch black and white. The reservoir capacitor would be made from the coatings on the inside and outside of the picture tube and need's to be less than 0.001 µF.
The heater is designed to be driven from the line output transformer and not connected as part of the normal heater chain.
The valve features a bell shaped anode cylinder with a wide separation to the cathode as befits such a high voltage device.
The screen can be seen to the right of the anode in this image.
The thin glass tube envelope is 20 mm in diameter and excluding the B9A base pins, is 66 mm in length.
References: Datasheet & 1040.

 

Pin Connections
B9A
1
2
3
4
5
6
7
8
9
tc
h,k,s
h
-
h,k,s
h
h,k,s
-
h
h,k,s
a

 

Absolute Maximum Operating Conditions
Diode
Vh
Ah
mAa
2.0
0.35
0.2
Thanks to Frank Philipse for supplying the above PDF datasheet.
Updated December24, 2016.
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