Tech Section: Evolution of Philco Model 19
The Philco Model 19 was in production for less than a year and a half (January 1933 through April 1934), and underwent a number of cabinet and circuit changes during this time period.
These circuit changes can be very confusing, especially since Philco only issued two Service Bulletins for this set, which do not cover all of the changes made to this model.
Before we begin to discuss the many circuit changes to Model 19, let's take a look at the various cabinets this model was offered in.
Evolution of Philco Model 19 Cabinets
Model 19B, January 1933
Model 19LZ, January 1933
Model 19LZX, January 1933
Model 19B, March 1933
Model 19H, June 1933
Model 19TX, June 1933
Model 19X, June 1933
Model 19X, July 1933
Model 19L, Fall 1933
Model 19X, January 1934
The earliest Model 19 sets with three knobs, receiving the AM band only, are Code 121 sets. The first Model 19 chassis installed in the 19LZ and 19LZX chairside cabinets are Code 122, with later models Code 123.
Some 19LZ and 19LZX chairsides have four knobs with AM and "police" band coverage. The code number of these chassis are not known at this time.
The most commonly found Model 19 set is Code 126; it has four knobs and receives the AM band and shortwave from 1.5 to around 3.3 mc. A version of this chassis, installed in the 19RX chairside cabinet, is Code 127.
The final version of Model 19 is Code 128. The parts layout under the chassis is very different than older versions, using two terminal boards holding individual paper capacitors and resistors instead of several bakelite block capacitors (a few bakelite blocks will also be found in Code 128 chassis).
There are very few documented changes for Model 19. Philco never published a schematic for Model 19 Code 126, although it is much different than older Model 19 versions. For some time now, this website has been the only source for a Model 19 Code 126 schematic (see the Schematics section). All of the changes the author is aware of may be found on this page, with accompanying schematics. Therefore this page is rather lengthy.
Click on any schematic below to see a larger image.
December 1932-January 1933:
Production of Model 19 begins. Introduced to the public January 1933. This is the original Model 19 schematic, as published in Service Bulletin 146 and in Rider's Manual:
Note that this schematic is identical to the earliest Model 89 schematic; the only difference is the addition of a shadowmeter and a pilot lamp to illuminate the shadowmeter screen.
It is doubtful that any were actually produced with the tone control shown above. The author has never seen a Model 19 chassis with a two-point tone control. Most likely, all early Model 19 chassis used the four-point tone control circuit as shown below.
Date unknown (possibly January-March 1933):
Resistor (42), part no. 4411 (99,000 ohms) changed to part no. 4409 (1 meg).
A .05 uF capacitor was added in parallel with the .09 uF section of capacitor (8). This capacitor was part no. 3615-L and was mounted between the antenna coil (2) and the RF tube socket.
In run number 2, Model 19-121; run number 3, Model 19-122; a 2900 ohm resistor, part no. 5309 was added. This resistor was connected between (8) condenser, lug no. 3 to lug no. 5 on the condenser mounted between (2) antenna transformer and the R.F. socket.
(The "condenser mounted between..." in this description refers to the .05 uF condenser, part no. 3615-L, added in the change noted for January-March 1933 above.)
Unknown date, 1933:
The following changes were made in 19-122 to make 19-123 under Run No. 1:
The sub base, part no. 8136, was changed to new sub base, part no. 29-1051. The tuning condenser assembly, part no. 06702, was changed to new condenser assembly, part no. 31-1004. The dial scale, part no. 8111, was changed to new dial scale 7882. The A.C. socket, part no. 5962, was removed. The bottom shield, part no. 8057, was removed. The two side brackets, part nos. 8133 and 8134 were removed. Four new mounting feet, part no. 4222, were added. The two electrolytic condensers, part no. 8095 were changed to part nos. 8165 and 8166.
March 15, 1933:
Antenna coil (2) changed from part no. 06619 to 32-1062.
Detector transformer (6) changed from part no. 06662 to 32-1063.
Volume control and off-on switch changed to volume control only (part numbers not known at present).
Combined off-on and waveband switch added, part no. 42-1002.
The above changes add a second band to Model 19, permitting police and airplace reception.
It is not definitely known at this time if these changes prompted a code number change to Code 126 or to a lower code number. However, the author is not aware of any Code 124 or 125 chassis in the Model 19 series. For now, therefore, I am going to consider this the official change to Code 126.
June? 1933: Model 19TX, Code 127.
The Philco Three Purpose Antenna System added to Model 19TX. Code 126 becomes Code 127 for this particular model. An antenna balun is added inside the chassis, mounted between the antenna transformer (2) and the multi-section metal condenser (7).
More details about this change may be found here.
June 15, 1933:
Condenser (45), part no. 3615-E, changed to 3615-BF. This is a change in lug arrangement for mounting only.
No change in Code 126 or Code 127 schematic.
October 15, 1933:
1st IF transformer (18) changed from part no. 06621 to 31-1289. Black and red leads to transformer reversed.
Resistor (48) changed from part no. 3525 (32,000 ohms) to 33-1027 (39,000 ohms).
Condenser (5), part no. 4989-W (.09 uF with 200 ohm resistor) changed to 4989-AG (.09 uF with 300 ohm resistor).
November 15, 1933:
Type K-7 speaker changed to K-21 in Baby Grand (cathedral) models, and H-9 speaker changed to H-15 in console models. Condenser (45), 3615-BF, is now removed.
Undated change (actual date this change went into effect unknown):
Resistor (10), part no. 6208 (15,000 ohms) changed to 4412 (10,000 ohms). Note that this change should be made to all earlier models of the 19 Series to improve oscillator performance.
Model 19 Code 128 goes into production. This version of the 19 uses a power transformer with a higher B+ output, giving the set an undistorted audio output of 5 watts compared to 3 in the earlier models. The under-chassis parts layout is quite different from earlier versions. The speaker is changed from K-21 to K-23 in the Baby Grand (cathedral) models, and from H-15 to H-16 in console models.
This prompted a revised schematic, as follows:
Undated change to Model 19 Code 128:
Correct Voltage Table as follows:
Plate voltages: 44s and 36: 225 volts; 75: 150 volts; 42: 270 volts.
Screen voltages: 44s and 36: 100 volts; 42: 290 volts.
No change in schematic.