In 1927-28 there were available on the market several short wave receiver kits which are easily assembled by the amateur set builder. One such kit of particular merit, designed and sold by Silver-Marshall, Inc., of Chicago, is known as "Round the World Four." This kit employs one stage of untuned radio frequency amplification preceding the detector tube. A description of the kit follows.
Description-- Silver-Marshall "730 Series" screen grid short wave kits were available in two models, both of which were designed around a type 732 Essential Kit. Both are identical in external appearance, being housed in the same type of aluminum shielding cabinet, 14 inches long, 6 inches wide and 6 inches high, and weighing 14 pounds. The 730 "Round the World Four" is a four-tube non-radiating short wave receiver consisting of one stage of screen grid r.f. amplification, a regenerative detector and two stages of extremely high-gain audio amplification.
coils, which may be successively plugged into a 5-prong tube socket on
top of the cabinet, provide four tuning ranges on the left-hand (tuning)
dial (131-T: 17.4 to 32 meters. 131-U: 31 to 58 meters. 131-V: 56 to 110
meters. 131-W: 105 to 204 meters).
on image below for actual photo of the radio.
The 731 "Round the World Adapter" is essentially a two-tube device used for short wave reception, when connected by an adapter to any broadcast receiver. Or it may be connected to a standard power audio amplifier, or used directly with headphones. The 731 adapter is exactly the same in appearance as the 730 four-tube set, and is substantially the 730 set except that the two-stage audio amplifier is omitted (but may be added at any time if desired). The wavelength range, tuning characteristics, distance range, etc., are the same for Model 731 as for Model 730.
Type 732 Essential Kit contains the essential parts for the r.f. portion of the S-M "Round the World" circuit. It may be assesmbled into a two-, three-, or four-tube receiver, as desired, either in the S-M type 734 aluminum shielding cabinet, or upon a wood baseboard, or in any other fashion.
Information is from "Radio Manual" by George E. Sterling, 1928. Edited for the Web by John Dilks, K2TQN.© 1999.
Click here to download
a better, complete 4-page article with a large schematic.
It's a 1 megabyte Adobe "pdf" file. (The schematic is 300 dpi so it prints well.)
This radio will be on display in K2TQN's OldRadio Museum.
Help: I need one more SM coil for this radio:
This coil has
Note #24 is fine
wire, #34 is even finer. The 131-W, in a photo I have,
looks like the #24 wire covers most of the top area of the form. I wouldn't
try to unwrap any turns to count them, just a good guess would be ok.
All of the other coils have a larger size wire, #22 (enameled).
I only received
one coil with the set and have since found two more.
If you have any to spare, I would be happy to purchase them.
- Thanks & 73', John Dilks, K2TQN