Note
Radio News, Jun 1929, p. 1147.
Radio News, Sep 1929, p. 273. (inside photo)
National replaced its original Thrill Box (unofficially called the SW-2) in June 1929 with a new version designated the SW-4 (also called a Thrill Box, and later desiganted SW-4, because it has four tubes). Not actually referred to as the SW-4 until September 1929. The big improvements were these:
— it permitted loudspeaker operation (although a version of the SW-2 would also drive a speaker)
— had decent audio
— covered both shortwave and the AM broadcast band
Tubes: (1) 222, (1) 200A, (1) 240, (1) 171A
Frequency coverage (in separate coils) originally expressed in meters, stated here in megahertz for convenience, approximately: 520 kHz–19.3 MHz
Coil A: 11.3–19.3 MHz
Coil B: 7.3–12.7 MHz
Coil C: 4.6–8.0 MHz
Coil D: 2.6–4.7 MHz
Optional coils
1.7 -2.7 MHz
1.0-1.7 MHz
0.52-1.0 MHz
Requires National's external "Velvet B" power supply.
+160 VDC
+135 VDC
+45 VDC
–45 VDC
and filament
References
Review. Radio News, Jun 1929, p. 1079.
Some Refinements. Radio News, Nov 1929, p. 443.