Prototype set is here

[John Folsom]

Nick, Here is a photo of the bottom side of he CBS prototype. It appears to use large high-voltage resistors, but it has been many years since I was under the chassis, so the details are vague. I have never had the HV cage cover off the Sparton, but as it appears to be a close cousin to the production Sparton set shown in Sames, I expect it will also have 50 megohm (or similar) high voltage resistors. Both of these sets are, shall we say, more mature than your set. :-)