siren circuit

[Andy]

Is John Popelish here? I changed the labeling since
my last post. I am still having difficulty to fully
grasp this circuit. My next questions are as follows:

I also removed the LED because we can see the simulation
without it, and it does not (I think) effect the analysis.

I have noticed that if we increase R2 from 47K to 2M the
circuit will still oscillate, but any further increase and
the circuit will not oscillate. I was wondering if I could
obtain a formula to calculate the maximum value (which is
2M by inspection of simulation results)

following is the lt spice asc file as modified by me:


Version 4
SHEET 1 880 680
WIRE 48 64 176 64
WIRE 240 112 240 320
WIRE 160 320 240 320
WIRE 240 320 240 384
WIRE 32 320 96 320
WIRE -48 320 -96 320
WIRE -96 320 -96 112
WIRE -16 112 -96 112
WIRE -96 112 -96 0
WIRE -96 -80 -96 -144
WIRE -96 -144 240 -144
WIRE 528 -144 528 -128
WIRE 240 -144 240 16
WIRE 240 -144 528 -144
FLAG 48 160 0
FLAG 240 464 0
FLAG 528 -48 0
SYMBOL res 224 368 R0
SYMATTR InstName R3
SYMATTR Value 50
SYMBOL cap 160 304 R90
WINDOW 0 0 32 VBottom 0
WINDOW 3 32 32 VTop 0
SYMATTR InstName C
SYMATTR Value .47ľ
SYMBOL pnp 176 112 M180
SYMATTR InstName Q2
SYMATTR Value 2N3906
SYMBOL res 48 304 R90
WINDOW 0 0 56 VBottom 0
WINDOW 3 32 56 VTop 0
SYMATTR InstName R2
SYMATTR Value 47k
SYMBOL npn -16 64 R0
SYMATTR InstName Q1
SYMATTR Value 2N3904
SYMBOL res -112 -96 R0
SYMATTR InstName R1
SYMATTR Value 4e6
SYMBOL voltage 528 -144 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V1
SYMATTR Value PULSE(0 9 0)
TEXT -114 506 Left 0 !.tran 10s