Before revision: The original design used the following tubes: Converter: 12A8 IF amplifier: 12K7 Detector and first audio amplifier: 12Q7 Audio power output: 50L6 Rectifier: 35Z4 This series had the grids brought out as top caps on the signal tubes, and the 35Z4 did not have a provision for a dial light.
After revision: 12AX7The original design used the following tubes: Converter: 12A8 IF amplifier: 12K7 Detector and first audio amplifier: 12Q7 Audio power output: 50L6 Rectifier: 35Z4 This series had the grids brought out as top caps on the signal tubes, and the 35Z4 did not have a provision for a dial light.