Aha!
found this link to the ERNIE specifications. http://www.tnmoc.org/sites/default/files/Ernie.pdf
It seems my guesses were right. The amplified noise was sent to a data slicer - much as my Schmidt does - and the pulses counted over a timing period.
perhaps I'll build a modern version ( using a semiconductor noise source, amplifier , Schmidt and arduino digital input ) and see what I get - perhaps we could compare results!
How did you test the data you obtained using a PC for randomness?
regards
Allan.