IF Transformer Pass Band Plots (see bottom of page for method)

ACME 30 KC, iron core

Experimenters Information Service Model C, iron core

Jefferson No. 150, iron core

RCA UV1716, iron core

Selectone R-400, iron core

Selectone R-410, air core

All American R-120, air core

Madison-Moore Unit No. 3, air core

Lincoln 1, air core

Lincoln 2, air core

Lincoln 3, air core

Lincoln 4, air core

Rusco 95KC, air core

Rusco 10KC Band Pass Filter, air core

     The above pass band plots were made with the assistance of a Wavetek sweep generator (Model 166), a Fluke oscilloscope, and an operational amplifier precision rectifier, or “super diode.” See the diagram below for the setup.

IF Transformer Pass Band Test Circuit

Notes:

1. The sweep time on the Wavetek generator was set at 900 milliseconds.
2. The start and stop frequencies are set on the Wavetek generator.
3. Wavetek output was set at approximately 100-300 millivolts (adjusted with each test to get maximum pass band peak at 100%).
4. The sweep time on the Fluke scope was set at 100 milliseconds/division (9 divisions = 900 milliseconds).
5. The Fluke scope was set on the one-shot mode (to save a trace for photographic purposes).
6. The output sync from the Wavetek generator triggers the Fluke scope trace on channel 2.
7. The precision rectifier changes the AC output signal of the tube to a DC value to be displayed on the Fluke scope on channel 1.
8. 01-A tubes are used to drive and load the test transformer in an attempt to simulate actual 1920s circuit conditions on the transformer.

     An alternate method of getting a pass band on an oscilloscope instead of using a precision rectifier is to use a common diode demodulator circuit. I tried the diode demodulator circuit after I took the above photos and discovered that the response of the diode demodulator circuit was nearly identical to the response of the precision rectifier. The diode I used was equivalent to a 1N34 with a forward voltage drop of .15 volts @ .2 milliamps. The diagram for the diode demodulator circuit (as used in place of the precision rectifier) is shown below.