Y.S.W.- 4A2 Shortwave Receiver


Frequency Range: 240 to 12 metres (1250 KHz to 25 MHz)
Type 38758-YSW-4a2
Spec: Spec 38759
Circa: 1933
Comment: If anyone can provide additional information, please contact:  jerry.proc@sympatico.ca

Above and below: Front panel views.
The model number is identified on the front panel. On top of the radio is additional identification which indicates Type 38758-YSW-4a2, Spec 38759 and wavelength range from 12 to 240 metres. 
This particular receiver came with four sets of coils covering 12 through 85 meters. A notation on the schematic says that two optional coil sets were available to cover the rest of the tuning range. 
The receiver was also accompanied with an internal factory memo dated April 22nd, 1933  and details alterations that were made "for operation with the automotive series of tubes". It uses 2 x 236, 1 x 237 and 1 x 238 type tubes. These are RCA's [1] version of the standard automotive types 36, 37, and 38. Other manufacturers of the period who made the 36, 37 and 38 tubes used their own designators.  As an example, Cunningham produced these tubes as 336, 337 and 338. Some 2xx series receiving tubes bear the prefix UY indicating the base type.

On the schematic, these tubes are designated as '236, '237 and '238 and a best guess says the apostrophe likely represents anything that the draughtsman wanted it to be. It could stand for RCA or UY [2] . The number 2 is a designator for the RCA company. To study the characteristics of these tubes, please refer to types 36, 37 and 38.

In the three interior photos above, the Range 2 (19 to 30 metre) coils are in place.
All photos in this table by Wayne Mackin 

Click to enlarge

ysw4a2_factory_letter_s.jpg This letter from Marconi details what changes are necessary in order for the YWS-4a2 receiver to use automotive type tubes. Of interest is the location from where the letter originated  because Canadian Marconi was headquartered in Montreal. It came from Yamachiche, just slightly west of Trois Rivières, Quebec. 
ysw4a2_schematic_s.jpg Schematic of receiver 
Letter and schematic provided by Wayne Mackin 


ysw4a2_uy236.jpg ysw4a2_uy237.jpg ysw4a2_uy238.jpg
UY-236 tube image (Courtesy e-bay) UY-237 tube image. (Courtesy e-bay) UY-238 tube image. (Courtesy radiomann)

[1] RCA was a patent pool corporation, not a manufacturer, until they bought the Victor Talking Machine Co. in 1928.  So the early RCA superheterodyne receivers were actually built by GE and

[2]  The prefacing of type 236 with an apostrophe to denote dropping the two-letter basing prefix would be understandable in the early to mid 1930's.  Things like that came along with the revision of the drafting standards for tube internals to show the plate as a straight horizontal line at the top rather than a rectangle on one side, and the grids as horizontal dashed lines, a general
standardization of broadcast IF frequencies in the 450-470 KHz range, and the wholesale shift from 2.5 to 6.3 volt heaters.

Contributors and Credits:

1) Wayne Mackin <wmackin(at)rogers.com>
2) UY238 image   http://www.geocities.jp/radiomann/HomePageVT/GRPJVp/US38.JPG
3) http://www.vacuumtubesinc.com/TubeTidbits/AntiqueTubeEquivalents.aspx
4) Robert Downs <WA5CAB(at)cs.com>
5) HankVan Cleef <hankvc(at)lostwells.net>

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Mar 21/10