LDM #219: Teardown and test of a Stall Warning Tone Generator from an Avro Shackleton

This video shows the teardown, schematic diagrams analysis and tests of a 6A/12860 Stall Warning Tone Generator. This device was manufactured in the early 70s. The manufacturer is unknown. This device was installed in an Avro Shackleton, maybe the first prototype S/N WL745.

00:00 - Intro
01:00 - Teardown
06:13 - Schematic diagram : Power Supply
07:40 - Schematic diagram : AOA sensor front end
09:03 - Schematic diagram :Tone Generator
13:04 - Tests
14:44 - Conclusion
15:10 - High quality audio recording (direct connection to the camera)

There are 2 identical boards containing a +/-12V power supply, the AOA sensor circuit and a relay for the stick shaker. One board is independent and connected to the circular connector.
The second board is in addition connected to the tone generator in order to produce a sound which changes with the angle of attack. A tone signal is frequency modulated with a modulation signal which frequency is a function of the angle of attack. When the angle of attack increases the modulation frequency increases. When the critical angle of attack is achieved the stick shaker is energized and the amplitude of the tone signal is increased by 10dB.

Pinout of circular connector (independent board, no tone output):

k: +28V
a: common for the +28V
p: +12V output
h: angle of attack DC input signal
m-a: output for the stick shaker

Pinout for the second board, with tone output:

E: +28V (300mA max)
X: common for the +28V
N: +12V output
g: angle of attack DC input voltage
R: audio output #1
S: audio output #2
m-D: contact relay for stick shaker

For testing: connect a 1k potentiometer between X and N, whipper connected to g