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Philco 37-690X De Luxe Super 'Hi-Fi' Console Radio (1936/37)
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Philco's High-Fidelity 37-690X De Luxe, introduced in
June of 1936, was their top-of-the-line receiver for the
1937 model year. It comprises a powerful 20-tube all-
wave radio housed in a spectacular twin-door cabinet of
classic design. The whole is appointed with a medley of
highly figured walnut, finished using the finest hand-rub-
bed lacquer. With the doors opened and stowed incons-
picuously to the sides of the cabinet, the inner instrum-
ent panel and grille are revealed as being in accord with
the best traditions of 1930's machine-aged design.
The 37-690X was initially priced at $375 in the Eastern
USA - about $6450 in today's dollars!
The 37-690X, along with the 38-690XX from the ensuing
year, have with the benefit of hindsight been acknow-
ledged as representing the pinnacle of Philco's engin-
eering accomplishments. They were the culmination of
8 years of progress made by Philco while developing a
line of domestic radios that had consistently fallen in
the upper echelons for quality and performance. All this
from a company more widely known for its production of
popular models, ones which had handily maintained
them in the number one position for radio sales in the
industry since 1930.
Observers today generally agree, with a few exceptions,
that Philco's 1937 and 1938 690 models sound as good
as, if not better than, almost anything else produced
during radio's golden era, regardless of price. A tribute
indeed to Philco and the quality of their engineering.
During this period, the company, under the leadership
of James Skinner, was a text-book case of how to do
things right, for whom almost everything touched seem-
ed to turn to gold.
One can highlight on a time-line the significant Philco
innovations culminating in the 37-690X in 1936. With
reference to a Philco marketing brochure for the 1937
line, this might run as follows:-
For 1936, the following innovations, all of which were
incorporated into the 37-690X, need adding:-
Technical Overview
The 5-band 37-690X uses 20 tubes divided between a
13-tube tuner chassis and a 7-tube power-supply and
amplifier chassis. The tube line ups and tuning ranges
are shown lower to the right. The set uses what were at
the time the new Octal-based glass tubes, developed
at Philco's urging as a counter to metal tubes from GE
and RCA.
The schematic, along with alignment details, etc. may be
found here, courtesy of NostalgiaAir. If you have a djvu
app (free downloads are available) a better copy is av-
ailable here (courtesy audiophool), though be aware
that there a some errors in this version.
A close up of the instrument panel is shown to the right.
The leftmost knob is the On-Off and Bass Control.
Audio Output: The audio output circuit uses two 6B4G
power triodes operated in class A and claimed to prod-
uce 15 Watts at less than 1.25% distortion. In their ad-
vertising Philco referred to the audio reproduction sys-
tem as being Super High-Fidelity, rather than merely
Super Class-A, as for their lesser class A models.
Bass Amplification: Three tubes are used for auto-
matic Bass compensation. These boost Bass output as
the set's volume is manually reduced, offsetting the dim-
inishing Bass perception of the human ear as volume is
lowered. A description of the circuitry is presented here,
courtesy of philcorepairbench. A continuously variable
bass control knob is provided to facilitate tailoring of the
overall bass response by the listener, forming part of
what Philco called their Musical Interpretation Control.
Loudspeaker System: This consists of a large prim-
ary loudspeaker, 4 acoustic clarifiers and a pair of high-
frequency speakers. The 14" electrodynamic cathed-
ral speaker serves as primary reproducer, surrounded
by the four 8" acoustic clarifiers, which are passive
devices used to absorb cabinet resonances and lessen
boom. All frequencies are applied to this main speaker.
A conically-shaped sound diffuser is placed in front of
it, concealed behind the grille cloth, to help disperse its
medium and high-notes evenly throughout the room.
This speaker's cone is formed as two concentric sect-
ions. The inner part is more rigid, serving to better rep-
roduce higher notes. Both sections, including the more
compliant outer section, handle the lows. A photo of a
similar loudspeaker is shown here.
The 6" electrodynamic high-frequency units handle most
of the high frequency output. They are energized by a
second output transformer placed between the plates
of the push-pull 6B4G tubes in parallel with the first. A
0.015uF capacitor in series with this transformer's prim-
ary serves to isolate these units from low bass notes.
For more details concerning Acoustic Clarifiers, see the
High-Fidelity Speaker paragraph under Technical
Highlights on my 38-116XX page.
The Inclined Sounding Board, the presence of which is
implied by the X in 690X, appears in fact to be NOT inc-
lined, so it is dubious as to whether the 690X deserves
its X. For more details on the Philco Inclined Sounding
Board and the 'X' descriptor, see my 112X page and
also Did the 690XX need the Inclined Sounding Board?
on my 38-690XX page.
Variable IF bandwidth: a fidelity control knob is used
to mechanically change the response of three of the
set's four IF transformers, allowing IF bandwidth to be
adjusted between approximately +/-2.0kHz & +/-7.5kHz,
as needed to accommodate standard and high-fidelity
broadcasts and to enhance selectivity during crowded
shortwave reception. This adjustment, together with a
ganged control offering more conventional tailoring of
high-frequency response, forms the treble part of the
690's Musical Interpretation Control.
Foreign Tuning System: This refers to aspects of the
front-end design concerned with optimizing sensitivity of
the set and its ability to tune and separate stations. In
these respects, the 690X is a class act.
Firstly, the set was designed to accept a balanced ant-
enna input from a device such as the Philco High-Effi-
ciency-Aerial-System. Each band has its own tuned ant-
enna input circuit, switched in and out by the waveband
selector switch for the purposes of matching receiver to
antenna and thereby maximizing the transfer of signal
energy into the receiver. Pick-up of noise radiated from
local wiring is also lessened through the use of this arr-
angement (because of the balanced feed between out-
side antenna and receiver). A less efficient unbalanced
antenna input is also provided for temporary use during
test, or for use by those not in possession of Philco's
High-Efficiency-Aerial. Philco's Aerial, incidentally, was
claimed by the company to be an integral part of the
Foreign Tuning System.
A second aspect is the use of a dial for which almost the
entire 360 degrees is marked, in color, with frequencies
and the names of stations. On many All-Wave sets only
half the dial was used for frequency markings and usu-
ally there were fewer bands to boot, with the result that
stations were far more crowded together. No wonder
Philco claimed "stations spread six times further apart" in ads
for the 690X. See the illustration of a spread-band dial
below right (unfortunately monochromatic for now).
Another aspect of FTS was the unit-construction tech-
nique adopted by Philco starting with this season. By
judicious grouping of the RF and mixer stages (includ-
ing LO) together on a separate sub-chassis that was
hosted by the main chassis, Philco claimed to improve
screening and minimize the length of interconnects,
thereby optimizing performance.
Automatic Tuning: The 690X incorporates Philco's
Automatic Tuning dial, introduced for the 1937 model
year. Refer to PhilcoRepairBench for details on this
dial's usage, setting up and service. The US patent for
this tuning device, #2248678, was filed on behalf of
Philco on Aug 6th 1936 and was granted on July 8th
1941. It names the inventors as Glaser, Bowman and
Briggs.
When the 1937 line was introduced in June of 1936, it
included three automatic tuning models; the 116X, 675X
and 690X, all referred to in Philco advertising as the De
Luxe models. The 116X and 675X were also offered with
standard dial tuning and these were not referred to as
De Luxe. In January of 1937 (mid season) three lower
priced automatic-tuning only consoles were added to
the line (9X, 10X & 11X), bringing the total such models
to 6. The standard versions of the 116X & 675X were
discontinued at this time. The new models were not
granted the distinction of being referred to as De Luxe.
Moreover, usage of De Luxe for the 690X appears by
this time to have fallen from favor, though it continued
to be used for the now automatic only 116X and 675X.
Like dialing a telephone but quicker and easier, Philco
said of this feature in their ads. Of course, tuning could
be accomplished manually for stations not preset for
automatic tuning or when just browsing the wavebands.
To facilitate this, sensitive two-speed vernier tuning is
possible using the concentirc knobs at the center of
the tuning dial (see control panel close-up, photo lower
right).
Magnetic Tuning: The 690X features an Automatic
Frequency Control (AFC) circuit, referred to by Philco
as magnetic tuning. This was primarily added to work in
conjunction with the Automatic Tuning dial mechanism
for the purpose of correcting residual tuning errors.
AFC on the 690X operates by sensing carrier frequen-
cy detuning relative to desired IF center frequency
(470kHz for the 690X), automatically adjusting the freq-
uency of the LO so as to drive any tuning errors tow-
ards zero. Three of the receiver's tube complement is
devoted to this operation. The AFC works well only with
medium-to-strong signals and a switch is provided on
the front panel to disable it during situations where rec-
eption is weak or when hopping between stations that
are crowded close together, such as encountered while
exploring the short waves. Once a strong shortwave
station was tuned in however, it could be locked in by
activation of the Magnetic Tuning. Philco claimed that
correct tuning was especially important in achieving the
transparency of tone that was realizable with High-Fid-
elity reception.
I purchased this radio through Ebay in 2007 from a sell-
er in Arkansas. It is in original cosmetic condition and
currently electrically unrestored.
June of 1936, was their top-of-the-line receiver for the
1937 model year. It comprises a powerful 20-tube all-
wave radio housed in a spectacular twin-door cabinet of
classic design. The whole is appointed with a medley of
highly figured walnut, finished using the finest hand-rub-
bed lacquer. With the doors opened and stowed incons-
picuously to the sides of the cabinet, the inner instrum-
ent panel and grille are revealed as being in accord with
the best traditions of 1930's machine-aged design.
The 37-690X was initially priced at $375 in the Eastern
USA - about $6450 in today's dollars!
The 37-690X, along with the 38-690XX from the ensuing
year, have with the benefit of hindsight been acknow-
ledged as representing the pinnacle of Philco's engin-
eering accomplishments. They were the culmination of
8 years of progress made by Philco while developing a
line of domestic radios that had consistently fallen in
the upper echelons for quality and performance. All this
from a company more widely known for its production of
popular models, ones which had handily maintained
them in the number one position for radio sales in the
industry since 1930.
Observers today generally agree, with a few exceptions,
that Philco's 1937 and 1938 690 models sound as good
as, if not better than, almost anything else produced
during radio's golden era, regardless of price. A tribute
indeed to Philco and the quality of their engineering.
During this period, the company, under the leadership
of James Skinner, was a text-book case of how to do
things right, for whom almost everything touched seem-
ed to turn to gold.
One can highlight on a time-line the significant Philco
innovations culminating in the 37-690X in 1936. With
reference to a Philco marketing brochure for the 1937
line, this might run as follows:-
- 1929 - first successful, practical Automatic Vol-
ume Control (in the model 95) - 1930 - tone-control; rubber-floated tuning con-
densors - 1932 - 6.3V tubes; introduction of Class A
amplification, bucking the industry wide trend
towards Class B that was predominant at the
time; the inclined sounding board - 1933 - introduction of the model 16 series of
all-wave receivers, considered among the best
ever made - 1934 - pioneered high-fidelity reception using
variable IF bandwidths; wide-angle sound diff-
using cabinet design - 1935 - Built-In-Aerial-Tuning system; Acoustic
Clarifiers; Precision Radio Dial
For 1936, the following innovations, all of which were
incorporated into the 37-690X, need adding:-
- 1936 - Foreign Tuning System and Philco's
- Spread-Band dial; Automatic Tuning,
helped by Philco Magnetic Tuning;
Three Speakers - one cathedral for Bass
and two high-frequency units (tweeters) -
for Super High-Fidelity; Octal-Based
Tubes
Technical Overview
The 5-band 37-690X uses 20 tubes divided between a
13-tube tuner chassis and a 7-tube power-supply and
amplifier chassis. The tube line ups and tuning ranges
are shown lower to the right. The set uses what were at
the time the new Octal-based glass tubes, developed
at Philco's urging as a counter to metal tubes from GE
and RCA.
The schematic, along with alignment details, etc. may be
found here, courtesy of NostalgiaAir. If you have a djvu
app (free downloads are available) a better copy is av-
ailable here (courtesy audiophool), though be aware
that there a some errors in this version.
A close up of the instrument panel is shown to the right.
The leftmost knob is the On-Off and Bass Control.
Audio Output: The audio output circuit uses two 6B4G
power triodes operated in class A and claimed to prod-
uce 15 Watts at less than 1.25% distortion. In their ad-
vertising Philco referred to the audio reproduction sys-
tem as being Super High-Fidelity, rather than merely
Super Class-A, as for their lesser class A models.
Bass Amplification: Three tubes are used for auto-
matic Bass compensation. These boost Bass output as
the set's volume is manually reduced, offsetting the dim-
inishing Bass perception of the human ear as volume is
lowered. A description of the circuitry is presented here,
courtesy of philcorepairbench. A continuously variable
bass control knob is provided to facilitate tailoring of the
overall bass response by the listener, forming part of
what Philco called their Musical Interpretation Control.
Loudspeaker System: This consists of a large prim-
ary loudspeaker, 4 acoustic clarifiers and a pair of high-
frequency speakers. The 14" electrodynamic cathed-
ral speaker serves as primary reproducer, surrounded
by the four 8" acoustic clarifiers, which are passive
devices used to absorb cabinet resonances and lessen
boom. All frequencies are applied to this main speaker.
A conically-shaped sound diffuser is placed in front of
it, concealed behind the grille cloth, to help disperse its
medium and high-notes evenly throughout the room.
This speaker's cone is formed as two concentric sect-
ions. The inner part is more rigid, serving to better rep-
roduce higher notes. Both sections, including the more
compliant outer section, handle the lows. A photo of a
similar loudspeaker is shown here.
The 6" electrodynamic high-frequency units handle most
of the high frequency output. They are energized by a
second output transformer placed between the plates
of the push-pull 6B4G tubes in parallel with the first. A
0.015uF capacitor in series with this transformer's prim-
ary serves to isolate these units from low bass notes.
For more details concerning Acoustic Clarifiers, see the
High-Fidelity Speaker paragraph under Technical
Highlights on my 38-116XX page.
The Inclined Sounding Board, the presence of which is
implied by the X in 690X, appears in fact to be NOT inc-
lined, so it is dubious as to whether the 690X deserves
its X. For more details on the Philco Inclined Sounding
Board and the 'X' descriptor, see my 112X page and
also Did the 690XX need the Inclined Sounding Board?
on my 38-690XX page.
Variable IF bandwidth: a fidelity control knob is used
to mechanically change the response of three of the
set's four IF transformers, allowing IF bandwidth to be
adjusted between approximately +/-2.0kHz & +/-7.5kHz,
as needed to accommodate standard and high-fidelity
broadcasts and to enhance selectivity during crowded
shortwave reception. This adjustment, together with a
ganged control offering more conventional tailoring of
high-frequency response, forms the treble part of the
690's Musical Interpretation Control.
Foreign Tuning System: This refers to aspects of the
front-end design concerned with optimizing sensitivity of
the set and its ability to tune and separate stations. In
these respects, the 690X is a class act.
Firstly, the set was designed to accept a balanced ant-
enna input from a device such as the Philco High-Effi-
ciency-Aerial-System. Each band has its own tuned ant-
enna input circuit, switched in and out by the waveband
selector switch for the purposes of matching receiver to
antenna and thereby maximizing the transfer of signal
energy into the receiver. Pick-up of noise radiated from
local wiring is also lessened through the use of this arr-
angement (because of the balanced feed between out-
side antenna and receiver). A less efficient unbalanced
antenna input is also provided for temporary use during
test, or for use by those not in possession of Philco's
High-Efficiency-Aerial. Philco's Aerial, incidentally, was
claimed by the company to be an integral part of the
Foreign Tuning System.
A second aspect is the use of a dial for which almost the
entire 360 degrees is marked, in color, with frequencies
and the names of stations. On many All-Wave sets only
half the dial was used for frequency markings and usu-
ally there were fewer bands to boot, with the result that
stations were far more crowded together. No wonder
Philco claimed "stations spread six times further apart" in ads
for the 690X. See the illustration of a spread-band dial
below right (unfortunately monochromatic for now).
Another aspect of FTS was the unit-construction tech-
nique adopted by Philco starting with this season. By
judicious grouping of the RF and mixer stages (includ-
ing LO) together on a separate sub-chassis that was
hosted by the main chassis, Philco claimed to improve
screening and minimize the length of interconnects,
thereby optimizing performance.
Automatic Tuning: The 690X incorporates Philco's
Automatic Tuning dial, introduced for the 1937 model
year. Refer to PhilcoRepairBench for details on this
dial's usage, setting up and service. The US patent for
this tuning device, #2248678, was filed on behalf of
Philco on Aug 6th 1936 and was granted on July 8th
1941. It names the inventors as Glaser, Bowman and
Briggs.
When the 1937 line was introduced in June of 1936, it
included three automatic tuning models; the 116X, 675X
and 690X, all referred to in Philco advertising as the De
Luxe models. The 116X and 675X were also offered with
standard dial tuning and these were not referred to as
De Luxe. In January of 1937 (mid season) three lower
priced automatic-tuning only consoles were added to
the line (9X, 10X & 11X), bringing the total such models
to 6. The standard versions of the 116X & 675X were
discontinued at this time. The new models were not
granted the distinction of being referred to as De Luxe.
Moreover, usage of De Luxe for the 690X appears by
this time to have fallen from favor, though it continued
to be used for the now automatic only 116X and 675X.
Like dialing a telephone but quicker and easier, Philco
said of this feature in their ads. Of course, tuning could
be accomplished manually for stations not preset for
automatic tuning or when just browsing the wavebands.
To facilitate this, sensitive two-speed vernier tuning is
possible using the concentirc knobs at the center of
the tuning dial (see control panel close-up, photo lower
right).
Magnetic Tuning: The 690X features an Automatic
Frequency Control (AFC) circuit, referred to by Philco
as magnetic tuning. This was primarily added to work in
conjunction with the Automatic Tuning dial mechanism
for the purpose of correcting residual tuning errors.
AFC on the 690X operates by sensing carrier frequen-
cy detuning relative to desired IF center frequency
(470kHz for the 690X), automatically adjusting the freq-
uency of the LO so as to drive any tuning errors tow-
ards zero. Three of the receiver's tube complement is
devoted to this operation. The AFC works well only with
medium-to-strong signals and a switch is provided on
the front panel to disable it during situations where rec-
eption is weak or when hopping between stations that
are crowded close together, such as encountered while
exploring the short waves. Once a strong shortwave
station was tuned in however, it could be locked in by
activation of the Magnetic Tuning. Philco claimed that
correct tuning was especially important in achieving the
transparency of tone that was realizable with High-Fid-
elity reception.
I purchased this radio through Ebay in 2007 from a sell-
er in Arkansas. It is in original cosmetic condition and
currently electrically unrestored.
The Most Faithful Reproduction Ever Achieved in Radio...
Feb 16th 1937, Altoona, PA
Colliers, Nov 28th, 1936
Philco Marketing Brochure Extract, June 1936
| PHILCO presents the 690X... designed, engineered, built with but a single thought in mind... to bring to its fortunate owner the boundless treasure the world of music... and the realm of radio... may bestow" |
RF Chassis (upper) Tube Line-Up:
6K7G RF amp
6L7G mixer
6A8G Local Oscillator
6N7G Osc control for magnetic tuning
6K7G 1st IF
6K7G 2nd IF
6J5G 2nd Detector
6B8G RF Automatic Volume Control (AVC)
6K7G Magnetic Tuning amplifier
6H6G Magnetic Tuning Discriminator
6J5G IF AVC
6J5G 1st AF
6K7G Automatic Bass Compensation Amp
Power Chassis (lower) Tube Line-Up:
5X4G Rectifier for first power unit
5X4G Rectifier for 2nd power unit
6J5G 2nd Bass amplifier
6F6G Driver
6R7G 2nd Audio ABAC
6B4G * 2 Push-Pull audio output
Tuning ranges:
Range 1: 530 to 1600 kcs
Range 2: 1.58 to 4.75 mcs
Range 3: 4.7 to 7.4 mcs
Range 4: 7.35 to 11.6 mcs
Range 5: 11.5 to 18.2 mcs
6K7G RF amp
6L7G mixer
6A8G Local Oscillator
6N7G Osc control for magnetic tuning
6K7G 1st IF
6K7G 2nd IF
6J5G 2nd Detector
6B8G RF Automatic Volume Control (AVC)
6K7G Magnetic Tuning amplifier
6H6G Magnetic Tuning Discriminator
6J5G IF AVC
6J5G 1st AF
6K7G Automatic Bass Compensation Amp
Power Chassis (lower) Tube Line-Up:
5X4G Rectifier for first power unit
5X4G Rectifier for 2nd power unit
6J5G 2nd Bass amplifier
6F6G Driver
6R7G 2nd Audio ABAC
6B4G * 2 Push-Pull audio output
Tuning ranges:
Range 1: 530 to 1600 kcs
Range 2: 1.58 to 4.75 mcs
Range 3: 4.7 to 7.4 mcs
Range 4: 7.35 to 11.6 mcs
Range 5: 11.5 to 18.2 mcs
| ..cabinet of classic design with full-length doors of four-way matched, highly figured butt walnut |
click any thumbnail to enlarge
The dial illustration,
right, taken from a
Philco marketing
booklet, is not that of
the 690X. It appears
to be that of the 116X
with standard dial
tuning. It has clearly
been modifed for illu-
strative purposes, as
the text advisories in
the lower section
would be inverted for
a true dial.
right, taken from a
Philco marketing
booklet, is not that of
the 690X. It appears
to be that of the 116X
with standard dial
tuning. It has clearly
been modifed for illu-
strative purposes, as
the text advisories in
the lower section
would be inverted for
a true dial.
Illustration of Philco Spread-Band Dial