Receptrad/Radio Receptor Co.

Receptrad Front View

     Victor Greiff, E.E., published a superheterodyne manual in early 1924 detailing the theory and manufacture of the superhet using his new Receptrad (Radio Receptor) parts. My example of the Receptrad was built by Charles A. Dean of Binghamton, N.Y., as proudly engraved on the front panel of the set. Charles A. Dean did a good job of building the set but he didn’t have access to the correct equipment to get it working the way it should have worked. Here are a few particulars of the set:

Receptrad Top View

     Top inside view of the set. The DPDT knife switch on the left side of the radio allows the operator to change from an external loop antenna to an external long wire antenna, with the long wire antenna utilizing an internal antenna coupler. When I purchased this radio it had five brass base tipped UV-201A tubes and one Airline gold glass tube. The brass base tipped tubes were probably five of the original tubes because they all had the same label attached with a date code of Jun 17 1924. All the tubes have good filaments.

Receptrad Top Angle View
Receptrad Antenna Coupler

Antenna coupler. The manufacturer is unknown.

Receptrad Oscillator Coupler

Radio Receptor oscillator coupler.

Receptrad Filter Transformer

     Inside angle view.

Receptrad IF Transformers

     Radio Receptor filter transformer. The builder forgot a very important thing; this transformer should have a .00025 mfd capacitor across the primary and secondary windings to make it peak at the correct frequency!

     Close up view of the first two non-tuned RF-1716 IF transformers. Note that the transformer on the right is identified with a Receptrad nameplate; the other transformers do not show the Receptrad name. It is obvious that the Receptrad transformer came from a different manufacturing lot than the other transformers. The Receptrad transformer peaks at a different frequency than the other transformers.

     Radio Receptor advertisement from the Fall, 1924, Citizens Radio Call Book.

Receptrad ad CRCB Fall 1924

Type

Peak Freq.

Lower 3 dB

Upper 3 dB

Bandwidth

Relative gain

Pri. ohms

Sec. ohms

#1, filter, with .00026 caps

39.8 KC

31,7 KC

46.1 KC

14.4 KC

16.0

107.1

106.3

#2, RF-1716

48.8 KC

35.2 KC

63.0 KC

27.8 KC

14.8

83.7

283.4

#3, RF-1716

28.0 KC

11.8 KC

54.2 KC

42.4 KC

18.4

135.6

333

#4, RF-1716

46.7 KC

32.3 KC

61.7 KC

29.4 KC

16.4

103.8

276.7

     The bandpass measurements of the IF transformers identified several problems with the set. The filter transformer was measured first and it was peaking at 99.0 KC. Victor Greiff’s book states that the filter transformer is designed to peak at 8500 meters (35 KC), with .00025 mfd capacitors across the primary and secondary coils. The capacitors were not there! I put a .00026 mfd capacitor across each coil and obtained a peak frequency of 39.8 KC. This frequency was better than before but the transformer may still need tweeking.
     The other three transformers, #2, #3, and #4, measured, in sequence, 48.8 KC, 28.0 KC, and 46.7 KC. The #3 transformer was way off mark at 28.0 KC. I thought that the transformer was a bad transformer. Several hours after the bandpass measurements I noticed that the label on the bad transformer was different than the label on the other transformers. The bad transformer was identified with the word Receptrad above the word Radio Receptor Co. I can only assume that one of the original transformers failed and was replaced with a transformer from a different manufacturing lot. The bandpass measurements are recorded in the table below.

     General Instrument tuning capacitor.

Receptrad Tuning Capacitor
Receptrad Front Panel Engraving

     Close up view of the front panel engraving.

     The two Radio Receptor audio transformers.

View of the label on one of the original BBT tubes.

Receptrad Audio Transformers
Receptrad BBT Tube Label

August 9, 2017 Update:

     The following images were scanned from Victor Greiff’s Super-Heterodyne Manual (Receptrad Series No. 1, 1st Edition, forward dated February 20, 1924). This book contained all the theory and full scale blueprints to construct the Receptrad Type SH8-1 superheterodyne.

Receptrad SH8-1 front and rear views

     Front and rear vies of the Type SH8-1 receiver.

Receptrad SH8-1 standard panel layout

     Type SH8-1 front panel layout. This is a photo of the original 36” long blueprint. Unfortunately, much of the detail is lost by reducing the original to this small size.

Receptrad SH8-1 standard baseboard layout

     Type SH8-1 baseboard component layout.

Receptrad SH8-1wiring diagram

     Type SH8-1 wiring diagram. The filaments of the three tubes of the IF amplifier are controlled with one rheostat and the filaments of the two tubes of the audio amplifier are controlled with one rheostat. The first detector, the oscillator, and the second detector each have their own filament rheostat control. The circuit includes a potentiometer to control the stability of the IF amplifier, and a small battery to control the grid bias of the two audio tubes. The first detector does not have a control for regenerative amplification. This is a typical early 1924 circuit. Regenerative amplification in the first detector was added to many superhets later in 1924.

Receptrad SH8-1 AF and RF transformer

AF and IF transformers

Receptrad SH8-1 Oscillator coupler
Receptrad SH8-1 Tuned Filter Coupler

Oscillator coupler

Tuned filter transformer
(my set did not have the capacitors)

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