Baldwin Pacific “Ranger” IF Transformers

Baldwin-Pacific Ranger IF Transformers

     A pair of old Baldwin Pacific transformers. A No. 25 transformer is at right and a No. 20 transformer (ID not certain) is at left.

     The factory specifications of the Baldwin Pacific “Ranger” transformers state that the IF frequency is 45 KC. The peak frequency of my No. 25 transformer was actually 50 KC. The peak frequency of the suspected No. 20 filter transformer was 115 KC with no capacitor. The secondary coil of this transformer has an inductance of 42.0 mH. A quick calculation indicated that a .000241 mfd capacitor in parallel with the secondary should make it peak at 50 KC. The actual capacitance required to peak the transformer to 50 KC was .000192 mfd.(this is due to the self-capacitance of the secondary winding, which appears to be about .00005 mfd.).

     The Baldwin Pacific “Ranger” transformers described here date to about August 1924. The two examples that I have show signs of a rough life. One of the transformers is identified as a No. 25 and the other transformer is unidentified (though its outward appearance is identical to the No. 25 transformer).

    The unidentified transformer has been repaired before. The DC resistance of the coils on this transformer is different than the DC resistance of the coils of the No. 25 transformer. The unidentified transformer has an air core and it peaks at a different frequency that the No. 25 transformer. All of the clues indicate that the unidentified transformer is the filter transformer of the “Ranger” series, a No. 20.

Baldwin Pacific Ranger No. 20 Transformer Inside View

     The photo at right is an internal view of the suspected No. 20 filter transformer.  The body of this type of transformer is made out of a heavy-gauge brass cylinder with formica end caps and its very easy to disassemble. The secondary winding is near the top of the transformer, or close to the terminals. The plate and grid leads are on the outside turn of their respective windings.


Peak Freq.

Lower 3 dB

Upper 3 dB


Relative gain

Pri. ohms

Sec. ohms

No. 25

50.0 KC

27.3 KC

93.6 KC

66.3 KC




No. 20, with no capacitor

115 KC

97.3 KC

136.5 KC

39.2 KC




No. 20, with a .000192 cap

50.0 KC

47.6 KC

52.1 KC

4.5 KC




Baldwin ad CRCB Fall 1924

     Baldwin Pacific advertisement from the Fall, 1924, Citizens Radio Call Book.

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