Version 4
SHEET 1 4432 680
WIRE 1664 -304 1440 -304
WIRE 1728 -304 1664 -304
WIRE 1728 -256 1728 -304
WIRE 1440 -224 1440 -304
WIRE 1664 -160 1664 -304
WIRE 1440 -80 1440 -144
WIRE 1504 -80 1440 -80
WIRE 1552 -80 1504 -80
WIRE 1664 -48 1664 -80
WIRE 1552 -32 1552 -80
WIRE 1440 48 1440 -80
WIRE 1440 48 1408 48
WIRE 1344 96 1264 96
WIRE 1664 112 1664 -48
WIRE 1664 112 1632 112
WIRE 1440 144 1408 144
WIRE 1264 176 1264 96
WIRE 1664 208 1632 208
WIRE 1440 256 1440 144
WIRE 1440 288 1440 256
WIRE 1440 384 1440 368
FLAG 1440 384 0
FLAG 1728 -176 0
FLAG 1552 32 0
FLAG 1664 208 0
FLAG 1504 -80 A
FLAG 1440 256 Out
FLAG 1264 256 0
FLAG 1664 -48 B
SYMBOL res 1248 160 R0
SYMATTR InstName R1
SYMATTR Value 10k
SYMBOL res 1424 -240 R0
SYMATTR InstName R2
SYMATTR Value 1Meg
SYMBOL voltage 1728 -272 R0
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName V1
SYMATTR Value 300
SYMBOL cap 1536 -32 R0
SYMATTR InstName C1
SYMATTR Value 20p
SYMBOL res 1424 272 R0
SYMATTR InstName R3
SYMATTR Value 75
SYMBOL res 1648 -176 R0
SYMATTR InstName R4
SYMATTR Value 300k
SYMBOL 2N2369A_Avalanche 1376 96 R0
SYMATTR InstName X1
SYMBOL 2N2369A_Avalanche 1600 160 R0
SYMATTR InstName X3
TEXT 1248 296 Left 2 !.tran 0 30u 0 100n uic
TEXT 936 400 Left 4 !.options reltol=0.01m  cshunt=20f
TEXT 1720 0 Left 2 ;Changing the value of R2 should be changed and the value of R1.