[BC] Pre 1960 radios...

[Mark Humphrey]

I have a 1957-vintage Stromberg-Carlson SR-406 with both selectable
bandwidth and the whistle filter.   When switched from normal to
"Hi-Fi" position, IF bandwidth increases from 7.5 to 15 kHz.

The notch filter is a simple LC network, shown in this schematic as
C37 and L23 below V8:

http://www.audiophool.cjb.net/Schem_A/S-C_SR-406_schem.gif

On the subject of car receivers, it's noteworthy that
Stromberg-Carlson was OEM of the 1959 Edsel radio, which featured
motorized tuning (with a "Town and Country" sensitivity switch) and
Germanium solid-state audio stage, but no IF bandwidth switching.
This was apparently the only car radio S-C made:

http://www.audiophool.cjb.net/MadeInRoch.html

Mark


On Sun, Aug 31, 2008 at 5:07 PM, Harold Hallikainen
<harold at hallikainen.com> wrote:
> Was it really necessary to drop the audio response down to 3 or 4kHz to
> get rid of a 10kHz whistle? Didn't radios in the 1930s have a 10kHz notch
> filter (possibly a twin-T)? Some radios had selectable bandwidth. In a car
> radio, the bandwidth select could possibly be tied to the instrument
> lights, which were already fed to the radio to light the dial.
>
>