Here's what I know about those stabilizers (which sound like the one
used on the GT6, and presumably the TR6 of the same late 60's early 70's era):
Mine is marked Smith's, and carries Smith's part number BR 1300/01, but
there were several slightly different units.
The manual claims that it stabilises voltage to 10V. It is mounted on
the rear of the speedometer case, and is presumably grounded through
the case (lead E).
The theory is that there is a heater coil wrapped around a bimetal
strip. One end of this is connected to terminal I (g/lg) and the other
is a set of points. 12V is supplied at terminal B (the green lead).
When the internal contacts are closed, current flows through the heater
coil to ground, which causes the bimetal strip to move and open the
points. This interrupts the current through the heater and allows the
points to close.
"The slow vibration of the bimetal strip results in an average
stabilized output voltage over a period of time at terminal I which is
a suitable supply for the slow reaction bimetal resistance type fuel
and temperature indication systems."
Oh, by the way:
"CAUTION: VOLTAGE STABILIZER SHOULD BE MOUNTED WITH B AND E UPPERMOST AND NOT
TILETED MORE THAN 20 DEGS. FROM THE VERTICAL IN EITHER PLANE." (their caps)
Connecting a voltmeter between I and earth will show a fluctuating voltage, not
constant 10V.
Presumably the electrolytic cap is there to protect the points from arcing.
I think Pat Vilbrandt posted a schematic a while back for making a solid state
version of this device...
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