The manual for these does turn up on epay occasionally. This one sold on May 16th 150813150406. Considering how many of these machines were produced over the years I was surprised at how little information seems available online. I knew you would find the manual useful, sorry I didn’t post about its existence in the gallery earlier, but I was slow to realise I could post.

It is common to see these machines fitted with modern replacement spade terminal silicon rectifiers and working well.  Original compounding rectifier for the 117 230V 50Hz has part No. 28111-549. I believe these to be selenium.

Try Arcol www.arcolresistors.com for a replacement slider.

Although some of these machines are still in service today, having given thousands of hour’s service they were an economy alternator. This type of compound excitation does not cope well with reactive loads. Page 12. It is however preferable to modern capacitive regulated crap. Output voltage is present between the auxiliary field and frame which is therefore more susceptible to low insulation resistance, whether or not the resin bonded field coils on some models had anything to do with addressing this I don’t know. Brush has a patent on a very similar excitation method, GB950106. I am not aware of another alternator manufacturer that used directly rectified load current compounding.
If I was to choose an excitation system used on small alternators which I thought had beauty of physics? Then the 1940’s development of the Magnicon by Macfarlane stands out. The peak of rotating electromagnetic voltage regulating technology, a member of the cross field rotating amplifier family. Admittedly a small full wave rectifier is required on ac machines for the control loop. Lost to history in less than a life time.