|These are the major differences between the 1963 TR-3 and the 1978 TR-4Cw/RIT:
- The TR-3 chassis is copper plated, while the TR-4Cw/RIT chassis is not. I believe Drake stopped copper plating chassis in the early 1970s, when the R-4C and T-4XC "C-line" separates were introduced.
- The TR-3 front panel is "reverse engraved" (the silver lettering is brushed metal that's higher than the painted parts, which are recessed slightly below the lettering), while the TR-4Cw/RIT front panel is the standard silkscreened type common to later Drake production.
- The TR-3 final cage is painted black, and has no top. The only cover over the final cage is that provided by the outer case. The TR-4Cw/RIT final cage is bright metal, with a separate cover (removed for the photos above).
- The TR-4Cw/RIT adds the following electrical features to the basic TR-3 design.
- CW sidetone
- True diode detection for AM reception (a step backward—the diode detection method is inferior to "exalted carrier" detection when the radio has no IF filter wider than the 2.1-kHz SSB filter)
- Provision for an optional noise blanker
- Receiver incremental tuning (RIT)
- Selectable 500-Hz CW filter
- A redesigned dial that shows 1-kHz calibration points directly on the dial, rather than on the tuning knob skirt
- A redesigned main tuning knob
- The ability to monitor relative RF power output on the PA plate current meter
- There are also several subtle electrical design changes in the TR-4Cw/RIT. These are the major ones:
- Final tubes are changed from 12JB6s to 6JB6s
- The PTO (permeability-tuned oscillator) is a solid-state instead of a "hollow-state" (vacuum tube) design.