Supertone/Buckwalter

Supertone Front View

     The Supertone was marketed in the late 1925 to 1926 time frame by the Buckwalter Radio Corporation. The radio is quite unique in several different ways. First and foremost is the use of a basepanel with machined grooves filled with a conductive copper material. It’s sort of like a printed circuit board but there was probably much more work involved in making this panel than its latter counterpart. In the 1920s it was illegal for most manufacturers to make a superheterodyne. Using a printed circuit to complete most of the wiring was possibly one attempt to get around the laws. The only thing a builder needed to do to finish this set was to connect a few loose wires.
     Another unique thing about this radio is the calibration of the two main tuning controls. Instead of being calibrated from 0 to 100, as most sets were at the time, the loop tuning control of the Supertone (the left dial) is calibrated in actual wavelengths and kilocycles (two scales). The oscillator tuning control (the right dial) is calibrated only in wavelengths, but there is two different scales that coincide with the two different frequencies of the oscillator that produce the desired IF. Here are a few more particulars of this set:

     Top inside view of the Supertone. This is a very clean looking set because most of the wiring is on the bottom of the basepanel.

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St. James IF Transformers<     HOME     >Tropadyne

     If you want to read more about the interesting history of the Buckwalter Supertone see an article on Nostalgia Air here.

Type

Peak Freq.

Lower 3 dB

Upper 3 dB

Bandwidth

Relative gain

Pri. ohms

Sec. ohms

#1, Filter .000482 cap

132.4 KC

116.2 KC

148.4 KC

32.2 KC

6.5

34.4

150.8

#2

140.0 KC

121.5 KC

164.0 KC

42.5 KC

8.0

51.9

149.5

#3

138.4 KC

107.6 KC

171.5 KC

63.9 KC

3.8

55.3

143.2

#4

144.6 KC

130.8 KC

158.4 KC

27.6 KC

8.4

52.4

148.5

     Notice that the wavelength scales on the two different dials are linear for wavelength divisions. This tells us that the Remler tuning capacitors are Strait Line Wavelength (SLW) capacitors. The Remler SLW tuning capacitors are the only capacitors that will work for dial calibrations of the Supertone.
     The oscillator dial has two different wavelength scales because there are two different oscillator frequencies that will mix with one particular signal frequency to produce the required IF frequency. In the case of the Supertone, one oscillator frequency is 140 KC above the signal frequency and one oscillator frequency is 140 KC below the signal frequency. The two different wavelength scales on the oscillator dial should be separated by a frequency of 280 KC. However, for some unknown reason the frequency difference or span between the two scales is slightly different at different positions on the scale; at the left side of the inner scale the difference is about 263 KC, near the middle of the inner scale the difference is about 293 KC, and at the right side of the inner scale the difference is about 252 KC. Those three different frequency spans equate to IF frequencies of 126 KC, 147 KC, and 132 KC, respectively. The IF frequency is certainly not changing so there must be some other explanation. Perhaps one or both of the wavelength scales are slightly nonlinear?
     An initial ohmmeter check of the IF transformers indicated that the first transformer had an open secondary winding. This was actually a good thing because it forced me to investigate the transformer and in the process I learned something. This style of transformer is very easy to repair; simply remove one nut from the end of the transformer and remove the phenolic tube. The problem turned out to be a tiny broken wire that was very easy to solder. I ended up examining all the transformers and can report that they all look similar.
     A bandpass check revealed that there was still a problem with the first transformer. The other transformers were peaking near 140 KC but the first transformer was peaking at 235 KC. The first transformer is the filter transformer and it has a .0005 mfd capacitor across the primary for tuning it to the correct frequency. The primary capacitor measured .00056 mfd and the primary inductance measured 3.24 mH (Ls=37.5 mH), which equates to a frequency of  118 KC. I put it all back together and it still didn’t work. With nothing left to try I replaced the old mica capacitor with a modern mica capacitor (.000482 mfd) and it worked! The old cap must have had some mechanical problem or leakage that the Sencore LC-53 didn’t detect.
     The table below records the bandpass measurements of the transformers. The first two transformers were measured with the secondary referenced to A- and the fourth transformer was measured with the secondary referenced to A+ (the grid leak resistor and capacitor were left in place). The #3 transformer had an unusually low gain and wide bandwidth. At first I thought it was due to some type of excessive losses in the transformer, and recorded such in my notes. However, when I was writing this section on the Supertone I suddenly realized that I had probably made a mistake in measuring the transformer. What was the mistake? The bias for the #3 transformer’s secondary coil is connected to the wiper of its own potentiometer (labeled “rheostat” on the front panel) and I hadn’t noticed it. The wiper was probably set a short distance from the A- side of the potentiometer.

  The loop tuning dial is calibrated in wavelengths and kilocycles.

     The oscillator tuning dial has two wavelength scales.

Supertone Loop Dial
Supertone Heterodyne Dial

Close up view of the engraved front panel.

   Inside view of the #1 IF transformer. Primary is close to terminals.

Supertone Front Panel Engraving
Supertone Filter Transformer Inside View

     Jefferson audio transformers.

   The number 1548 is engraved on the back side of the front panel.

Jefferson Audio Transformers
Supertone Back of Front Panel 1548

     Close up view of the copper traces.

     Close up side view of the oscillator coupler.

Supertone Copper Traces
Supertone Oscillator Coupler

     Bottom view of the chassis showing the copper channels/traces. The wiper of both potentiometers go to the IF transformers.

Supertone Bottom Chassis View

     Rear angle view of the chassis. The IF transformers are at the bottom right and the audio transformers are at the bottom left.

Supertone Rear Angle View
Supertone Top View 1