The RCA model 7-BX-10 Strato-World is a Zenith Transoceanic "clone" that is rather well-made. Like the Zeniths, it covers AM broadcast, two wide shortwave bands, and the 16, 19, 25, and 31 meter international "world-band" shortwave bands. The latter 4 are called spread bands, each covering a relatively narrow section of the short-waves thus eliminating the need for a separate "bandspread" function.
Like the Transoceanics, the RCA Strato-World is quite sensitive for shortwave listening with just the built-in telescoping whip antenna if the radio is working well. The tube complement is the same as found in the typical Transoceanic with 3V4 audio output, 1U5 detector/AVC/ audio preamp, two 1U4 for RF and IF amplifiers, and the expensive 1L6 converter.Schematic, alignment and other information can be found in Sams Photofact 248-14. The version in Sams does not include the filament-type ballast tube 50A1. This set does have the 50A1 tube indicating it was a later model improvement.
This set did not work at all. I cleaned all the controls including the bandswitch with deoxit. As I typically do with these sets, I powered it up on DC from a regulated high voltage supply while monitoring the filament voltage. Found the filament voltage going too high and somewhat unstable despite relatively low voltage input. Suspected dirty tube filament contacts creating high resistance in the filament series line. Wiggling a couple of the tubes in the socket confirmed the suspicion. The voltages stabilized after cleaning the tube and socket contacts and the set began playing.
Aligning this set is not for the faint of heart. It is a bit more complex than the Transoceanic. The Sams Photofact helps a great deal but leaves out the location for a couple of the coils. I had to rely on the wiring and the band switch contacts to pick the right coils and caps to adjust. Do not attempt alignment without full instructions.
This set has a separate set of plates in the tuning cap variable for the spread bands. I consider this an improvement to the original Transoceanic circuit. The little adjustable trimmer is critical to proper alignment because its capacitance is a significant portion of the two-plate cap. Just a bit of a turn can totally misadjust the oscillator setting for the spread bands.Like the Transoceanics, this set does well at pulling in shortwave broadcasts with good sound given its circuitry. It is also excellent at BC broadcasts.
The dial string was missing on this set. I redid the dial stringing according to the Sams Photofact diagram but the dial pointer does not travel the full length. If you have restrung this set and did not experience this problem, let me know.
Comparison to the Transoceanics
The RCA has Bass and Treble knob controls instead of the Zenith's slide switches for tone. The RCA is also housed in a shielded aluminum case covered in leatherette plastic with a nice world map in the lid. Both use a loop antenna for AM broadcast. The RCA loop is in the lid with connections made through the hinges but the antenna is not removable. It has a separate plastic-encased loopstick antenna with suction cups for attachment to a window. It comes complete with a length of red twin lead, the same color as that in the Transoceanic. Even the plug connector for the loopstick antenna is copied. The loopstick assembly has a built-in trimmer cap.
In subjective performance tests, I found the RCA to be the equal of the Transoceanic. Both use the critical and expensive 1L6 and both suffer at the high frequencies if the 1L6 and its oscillator/ converter circuit is not up to par.
A Zenith H-500 Transoceanic was the previous item on the bench.