Oddball circuit designs encountered in antique radio....please share!

[Old1625]

Have any of you encountered odd designs in antique radio? Please share what you have found!

I remember an old Philco floor model radio with slicer changer that had some unique features. In Rider #13 Philco model 42-1008,9 seems to match what I remember seeing in that old set I had as a kid. The chassis employed all loctal tubes except for a pair of 41s at output.

One design kink I've not often seen is the method of exciting the negative-order output tube in the push pull circuit. Instead of a balancing exciter, or using a split-load inverter or LTP type, Philco used a resistor to slightly undecouple the screen grid of the tube fed by the previous audio stage, and drew inverted signal off the screen to drive the grid of the second tube.

An even more interesting feature was the use of a specially-powered lamp and light cell in the head of the tone arm with a small mirror affixed to the stylus holder. The change of light falling on the cell with the movement of the mirror was amplified as a signal in a succeeding stage. the lamp had its own special power supply, as feeding off the filament line would introduce a flicker and resultant hum.