Note
QST, Dec 1967, p. 127. (R-4B)
QST, Mar 1973, p. 119. (R-4C)
The R-4B continued with the same basic setup of earlier R-4 receivers, but made increasing use of solid-state technology with 9 tubes, 10 transistors, 17 diodes, and 2 ICs. Solid-state devices were used in the PTO, crystal oscillator, AVC, BFO, crystal calibrator, and audio amplifier. There was a new tuning knob as well as cosmetic front-panel differences.
References
Brief description (R-4B). Popular Electronics, Oct 1968, p. 54.