These are being made locally by a retired engineer and British Car enthusiast and they are a much needed improvement! He has designed a custom printed circuit board for the application and sourced the best parts for the job. These units are put into refurbished original cases. He has sold over 50 and had nothing but good reports. There are other aftermarket versions of this, but there have been know quality issues with these. This 10 volt Analog Voltage Stabilizer is designed to directly replace the original electromechanical voltage stabilizer offering solid state dependability and accuracy to your British car. 
Positive ground only. This was never used on Positive ground Spridgets, but was on other British Sports cars.
Features…
-The unit is a drop in replacement with all electrical and mechanical connections in the same relative position as the original equipment.
-The solid-state regulator used is designed for use in the automotive environment.
-Reverse polarity protection
-Withstands current surges occasionally encountered during battery jumps.
Specifications…
Input voltage: 11.5-15 volts DC
Output Voltage: 9.90-10.0 volts DC