PHILCO PHORUM

Evolution of the Philco Model 60

NOTE: THIS IS A VERY LARGE PAGE WITH MANY GRAPHICS. PLEASE ALLOW TIME FOR ALL OF THE IMAGES TO LOAD IF YOU HAVE A SLOW CONNECTION.

The Philco Model 60 was in production for nearly three years (July 1933 through April 1936), 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, both of which are nearly identical and do not cover the later changes.

Before we begin to discuss the many circuit changes to Model 60, let's take a look at the various cabinets this model was offered in.

Of course, the photo above does not take into account the two console models (60L & 60F), nor the radio-phonograph using the 60 chassis (Model 505L).

CHANGES IN MODEL 60 CIRCUITRY

All Model 60 sets are labeled CODE 121, in spite of the many changes in its circuitry!

ALL of the documented changes made to Model 60 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.

Here is the original Model 60 schematic.

This schematic corresponds with the one in Service Bulletins 164 and 164-A. Note that only very early production 60 receivers (Run No. 1) have condenser (43) and resistor (44) in them.

Note the original trimmer condenser locations under the chassis, as shown below.

First change, Run No. 1:

Condenser (43) and resistor (44) removed. Around this time, an 800 pF fixed mica condenser (not shown in these schematics) was added across trimmer condenser (11), the low frequency police band padder.

August 1933, Run No. 2:

A 0.2 uF paper capacitor was added as shown above in red.

August 15, 1933 - Run No. 3:

The 0.2 uF condenser becomes part of filter condenser bank (20).

September 15, 1933 - Run No. 4:

Electrolytic condenser (45) changed from part no. 7558 to part no. 30-2024. Electrolytic condenser (46) changed from part no. 7558 to part no. 30-2045. No change in capacity of either (8 uF). No change in schematic.

October 1, 1933 - Run No. 4:

Trimmer condenser (11) removed (along with the 800 pF mica condenser connected across it). Both are replaced with a single 1400 pF mica condenser, Part No. 7007, connected from 3rd terminal of Wave-Band Switch to ground at condenser (7). Change above shown in red.

November 15, 1933 - Run No. 6:

The following changes were made to improve selectivity.

1st IF transformer (16) changed from Part No. 32-1049 to Part No. 32-1304.
2nd IF transformer (25) changed from Part No. 32-1050 to Part No. 32-1305.
A compensating condenser is added across the 2nd IF secondary (change above shown in red), Part No. 04000-M.
1st IF primary compensating condenser (17) changed from Part No. 04000-M to Part No. 04000-A.
1st IF secondary compensating condenser (18) changed from Part No. 04000-A to Part No. 04000-M.
2nd IF primary compensating condenser (26) changed from Part No. 04000-M to Part No. 04000-A.
Layout of trimmers under chassis changed as shown below.

August 1, 1934:

Resistors (10) and (28) changed from Part No. 4518 (51K, 1/2 watt) to Part No. 6098 (51K, 1/3 watt). This facilitates assembly of set in factory. No change to schematic.

August 15, 1934, Run No. 7:

The following changes were made to improve sensitivity.

A wavetrap was added in series with antenna post.
Resistor (9), Part No. 7217 (200 ohms), changed to Part No. 33-3010 (300 ohms).
Condenser (8), Part No. 4989-Z, removed.
Connection between cathodes of 6A7 and 78 tubes removed.
400 ohm resistor, Part No. 33-3016, added between 78 cathode and ground.
.05 uF condenser, Part No. 30-4020, added between 78 cathode and ground.
Resistor (24), Part No. 3656 (25K) changed to Part No. 33-1027 (39K).
Resistor (22), Part No. 4412 (10K), removed. There is now a direct connection between resistors (19) and (24).
Resistor (19), Part No. 4518 (50K) changed to Part No. 6099 (100K).
Filter Condenser Block (20), Part No. 30-4063, changed to Part No. 30-4217. The new block has four condensers instead of five; the 0.2 uF section having been removed. One 0.09 uF section of the block is now connected between the 6A7 cathode and ground.
All of these changes are shown in red in the schematic directly above.
Compensating condenser (18), 1st IF secondary, changed from Part No. 04000-M to Part No. 04000-J.

The changes result in a new trimmer condenser layout, as shown below:

December 1, 1934:

Suppressor grid of 78 Tube disconnected from cathode and connected direct to ground. Permits use of 78-E (European) tube interchangeably with regular 78. Change shown above in red.

January 1, 1935:

Dial scale changed from Part No. 31-1090 to a larger scale, Part No. 31-1472. Model 60 sets received a new, larger escutcheon at this time to accommodate the larger dial scale. No change in schematic.

June 1, 1935, Run No. 11:

The following Part Nos. were changed to allow use of the newer type bakelite block condensers with all lugs:

No change in schematic.

June (?) 1935:

Tube shields changed from cylindrical to rectangular. No change in schematic.
Dial scale changed from Part No. 31-1472 to Part No. 31-1792.

October 1, 1935, Run No. 11:

Tube Shield No. 28-2726 and Tube Shield Base No. 28-2725 for the 6A7 tube were deemed unnecessary, and were removed.

Changes in Part Numbers as outlined below:

No change in schematic.