1. Introduction

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.

Evolution of Philco Model 60 Cabinets

Model 60B, July 1933

Model 60L, July 1933

Model 60B, January 1934

Model 60MB, January 1934

Model 60B, 1935 (June 1934)

Model 60B, 1935 (July 1934)

Model 60B, 1936 (June 1935)

Model 60F, 1936 (June 1935)

Model 60B, January 1936

2. 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 in this thread, with accompanying schematics.

Click on any schematic below to see a larger image.

June-July 1933:

Production of Model 60 begins. Introduced to the public around July 1933. This is the original Model 60 schematic, as published in Service Bulletins 164 and 164-A, and in Rider’s Manual:

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 below in red.

3. Changes in Model 60 Circuitry, Continued

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 below shown in red.

4. Changes in Model 60 Circuitry, Continued

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 below 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 in 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.

Compensating condenser (18 ), 1st IF secondary, changed from Part No. 04000-M to Part No. 04000-J.

All of these changes are shown in red in the schematic directly below:

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

5. Changes in Model 60 Circuitry, Conclusion

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 below 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? 1935:

Tube shields changed from cylindrical to rectangular.

Dial scale changed from Part No. 31-1472 to Part No. 31-1792.

No change in schematic.

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.