Philco Model 70 Baby Grand Cathedral Radio (1931)
The Philco Model 70 Baby Grand was first offered for
sale in June of 1931, at the same time as its big brother,
the model 90. It employed Philco's 7-tube "balanced
superheterodyne" chassis, the entry level offering in
their line-up of 7, 9 and 11 tube designs for 1931/32.
As usual, Philco worked hard to foster the notion that
their sets offered something more than those of the
other manufacturers of the day. One way they did this
was through the liberal use of the word "plus" in their
advertising. It was a strategy that had proven success-
ful in the past with their "neutrodyne plus" and "screen
grid" plus, and so now came "superheterodyne plus".
Although strictly this referred only to their 11-tube sets,
they nevertheless used the word "plus" when promoting
their lower tube count models, combining it with "balan-
ced", another of their favorite words, as seen in the
following extract clipped from Baby Grand advertising:-
sale in June of 1931, at the same time as its big brother,
the model 90. It employed Philco's 7-tube "balanced
superheterodyne" chassis, the entry level offering in
their line-up of 7, 9 and 11 tube designs for 1931/32.
As usual, Philco worked hard to foster the notion that
their sets offered something more than those of the
other manufacturers of the day. One way they did this
was through the liberal use of the word "plus" in their
advertising. It was a strategy that had proven success-
ful in the past with their "neutrodyne plus" and "screen
grid" plus, and so now came "superheterodyne plus".
Although strictly this referred only to their 11-tube sets,
they nevertheless used the word "plus" when promoting
their lower tube count models, combining it with "balan-
ced", another of their favorite words, as seen in the
following extract clipped from Baby Grand advertising:-
...a superheterodyne receiver PLUS balanced units PLUS balanced tubes.
chassis is 35 (RF amp), 24 (mixer/LO), 35 (IF), 27 (rectifier-detector), 35 (detector-amp), 47 (output pentode) and 80 (rectifier). The
mixer and LO, which used separate tubes in the earlier chassis, were combined into one self-oscillating type 24 (autodyne) stage and
the 2nd detector was reconfigured to use a detector-rectifier and detector-amp for the AVC. For a description of the Philco "multiplex
detector" see the lower part of my Philco 111 page.
My radio, photographed above, has the more common early version of the chassis, with no AVC. The schematic may be found here.
mixer and LO, which used separate tubes in the earlier chassis, were combined into one self-oscillating type 24 (autodyne) stage and
the 2nd detector was reconfigured to use a detector-rectifier and detector-amp for the AVC. For a description of the Philco "multiplex
detector" see the lower part of my Philco 111 page.
My radio, photographed above, has the more common early version of the chassis, with no AVC. The schematic may be found here.
Copyright TubeRadioLand.com
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| "At Last! A radio that truly meets the modern demand for performance, a superheterodyne receiver PLUS balanced units PLUS balanced tubes. ... Remember, superheterodyne is not enough. It takes Philco's BALANCED superheterodyne to meet the modern demands of crowded broadcasting conditions". |
The model 70, with an initial purchase price of $49.95
complete with tubes, would go on to sell almost
300,000 sets - another huge success for the company.
The cabinet was first introduced in March of 1931 for
the model 21. However with the debut of the 70 & 90
in June the 21 was discontinued, with the result that
it's by far the rarest of the trio today. The cabinet was
designed by Edward Combs and has gone on to
become one of the most well-known of all cabinet de-
signs from the tube radio era. A copy of the Combs
design patent can be seen here.
The 70 was available in either walnut or mahogany
veneer.
The model 70 covers the standard broadcast band
from 550-1500kc. For initial production, through until
early 1932, the 70 used a type I chassis having tube
complement 24 (RF amp), 24 (mixer), 27 (LO), 24 (IF
amp), 24 (2nd detector), 47 (audio pentode) and 80
(rectifier). It did not use the Philco "multiplex detector"
and therefore did not provide automatic volume
control (AVC). Later production, above serial number
B-22,000, adopted an improved chassis that did
feature the "multiplex detector" for AVC, along with
variable-mu tubes. The tube line-up for this type II
complete with tubes, would go on to sell almost
300,000 sets - another huge success for the company.
The cabinet was first introduced in March of 1931 for
the model 21. However with the debut of the 70 & 90
in June the 21 was discontinued, with the result that
it's by far the rarest of the trio today. The cabinet was
designed by Edward Combs and has gone on to
become one of the most well-known of all cabinet de-
signs from the tube radio era. A copy of the Combs
design patent can be seen here.
The 70 was available in either walnut or mahogany
veneer.
The model 70 covers the standard broadcast band
from 550-1500kc. For initial production, through until
early 1932, the 70 used a type I chassis having tube
complement 24 (RF amp), 24 (mixer), 27 (LO), 24 (IF
amp), 24 (2nd detector), 47 (audio pentode) and 80
(rectifier). It did not use the Philco "multiplex detector"
and therefore did not provide automatic volume
control (AVC). Later production, above serial number
B-22,000, adopted an improved chassis that did
feature the "multiplex detector" for AVC, along with
variable-mu tubes. The tube line-up for this type II
| "pentode output tube for extra power, tone control, electro- dynamic speaker and illuminated station-recording dial". |