With the help and advice of Stanley, I have just installed a Balmar MC-614 regulator to control the ISKRA 100 Amp alternator on my Beta 50.
The process was straighfoward. First remove the existing, in built regulator, from the alternator, and replace it with a brush box.
The yellow wire from the brush box, is the field connection, and the other, black wire, is the stator output. On the Beta 50, there is an unused, brown wire, coming from the keyswitch which is easily accessed, and this provides the ignition input to the MC-614. It is possible to take the tacho signal from either the alternator or the MC-614.
Programming is simple and quick,and tailors the regulator's characteristics to your battery type and usage.
The whole job was completed in a few hours, and has made a dramatic improvement in charging efficiency.
I have found a very good article on this:bennersadrift.blogspot.com/.../modding-iskra-100-amp-alternator.ht... It has great photos and a good clear description of the job.
P.S. I was unable to get the tachometer to work through the MC-614, but it works just fine directly from the alternator.
