Philco Model 51 Baby Grand Cathedral Radio (Jan 1932)
The Philco model 51 Baby Grand was introduced
midway through the 1932 season, in Jan of 1932.
It was an evolution of the successful 1931 model
50, replacing that model's outdated TRF screen-
grid chassis with a new state-of-the-art 5-tube
"balanced superheterodyne" design and utilizing
an upgraded cabinet, offered in genuine hand-
Its initial selling price was $39.95 (complete with
tubes) and, considering that the TRF model 50's
introductory list price was $36.50, it's no wonder
that Philco bragged that the 51 was one of the
most tremendous values ever offered in radio
and that you have never heard of such a price
for such a radio. Other features of the 51 were
billed as superheterodyne selectivity.... screen-
grid power...genuine electrodynamic speaker...
5 Philco balanced tubes, including new pen-
ode...and Philco Balanced Units throughout.
Ultimately, some 23,800 model 51 Baby Grands
were manufactured and sold, so it was not an
overwhelming marketplace success.
The 51's chassis was also used for the model
551 Colonial Clock and a Philco 51 Lowboy.
Later in the year it would be placed into the new
model 52 tabletop and console radios too.
The radio covers the standard broadcast band
from 550 to 1500kcs and the tube line-up is 24
(mixer & LO), 35 (IF), 24 (detector), 47 (power
output), 80 (rectifier). The schematic can be
found here, courtesy of NostalgiaAir.
Although the 51 was state of the art for a 5-tube
set in 1932, its circuitry did not yet demonstrate
the degree of evolution that later 5-tube superhets
would show. The functions of oscillator and mixer
had been combined, making use of a self-oscillat-
ing type 24 tube in an arrangement known as the
"autodyne", but it would not be until April of 1933
that the much superior pentagrid-convertor tube
would arrive, in the guise of the 2A7 and shortly
thereafter the 6A7. Moreover, the model 51's sec-
ond-detector was based upon plate-detection
using a type 24 screen-grid tube, which does not
furnish a DC voltage proportional to the strength
of the received carrier, so the set has no AVC.
Nevertheless, Philco's 5-tube super-heterodyne
circuit was advancing nicely down the path leading
to what would later be the AA5 standard. Besides,
what was important for Philco in 1932 was that it
did work quite well and proved capable of being
successfully mass produced.
Philco 51B ...one of the most tremendous values ever offered in radio.
Feb 16th 1932 ad
Jan 15th 1932 ad
Mar 4th 1932, Pa
Note: shows model 90
instead of model 70.
click any thumbnail to enlarge