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Appeared in "Antique Radio Classified", October, 1994 Vol. 11, No.10

  Doerle 2-Tube Regen

   As a member of the Antique Radio Club of Illinois, I became interested in the historical aspects of the early days of commercial and shortwave broadcasting. After reading articles in many of the 1930's radio books and magazines of the era, I decided to try my hand at building a "home-brew" radio. Vintage parts and junker sets are still available at hamfests, swap meets and flea markets. Using original parts and hardware for this project would be fun and give me a sense of what it was like to build a regenerative tube radio from scratch.

Considering the age of the parts needed was fifty to sixty years, finding all the right parts was going to take time. It took over a year and a dozen swap meets, auctions, hamfests to track down the parts. Radio parts manufacturers like I.R.C., Cornell-Dublier, Carter, Kurz-Kasch, Eby, Hammarlund, Pilot, National and Yaxley show the variety of parts available sixty years ago. Some of the parts needed restoring themselves in order to make the radio look "new". Any corrosion or scratches would detract from the overall look and feel of the set. I wanted to preserve the sense of artistry and design that early builders used.

After looking through many reprints, I picked a 2-tube regenerative circuit popularized by Walter C. Doerle in the early 1930's see Fig. 1. A combination of two of the designs in The Hammarlund 1937 Short Wave Manual, and additional information from two other sources was used in the construction. Hints and tips on design from the Short Wave Beginner's Book and coil designs from the Short Wave Coil Data Book were also used. To simulate a vintage radio buffs' search for parts where he could find them, I selected many different parts' manufacturers (see parts list).

Fig. 1 Doerle 2-Tube Regen Schematic Diagram

The two triode tubes are used as a regenerative detector and an audio amplifier. I wound a set of five plug-in coils covering the standard broadcast band and the most popular international shortwave bands. Except for some screws, the oak base and phenolic front panel, all the parts are either used originals or new old-stock parts see Fig. 2. The hook-up wire was even re-cycled from a vintage tube tester chassis. During construction, I received valuable information and tips from club members and friends.
Rear View Doerle 2-Tube Regen

After construction, I attached the antenna, ground and battery wires to the set hoping it would not melt down on the first try. Unfortunately, there was only one small plume of smoke that rose from the regeneration potentiometer. There was no damage to the set, however. After correcting my error, I heard local AM stations coming through loud and clear. Tuning was sharp and the sensitivity was much better than I expected.

In the evening, distant AM stations like KMOX in St. Louis and KOA in Denver were not hard to pick up. The shortwave performance was surprisingly good as well. Catching a dozen or more stations from around the world wasn't more difficult than using a commercially built radio. Without any dial calibrations to go by, searching for stations in the shortwave bands gave me a feel for how it was done by early radio experimenters. This radio has heightened my appreciation and enjoyment of the hobby and I would encourage others to give it a try.

Doerle 2-Tube Regenerative Parts List

C1 - 140 pF. variable, BANDSET, Hammarlund MC-140-M
C2 - 35 pF. variable, BANDSPREAD, Hammarlund MC-35-S
C3 - 100 pF. / 400 v. mica, Sangamo
C4 - 35 pF. variable, ANT. COMP., Hammarlund HF-35
C5 - 250 pF. / 400 v. mica, Cornell-Dublier
C6 - 0.1 uF. / 600 v. paper, Aerovox
R1 - 3 Meg ohms, 1/2 w. carbon, Lynch
R2 - 10 ohm rheostat, FIL ADJ, Amsco
R3 - 50 K ohms, var., REGEN, IRC
R4 - 200 K ohms, 1/2 w. carbon, IRC
RFC - 2.5 uH. choke, National
T1 - 10:1 audio transformer, Rauland R-13, "All-American"
V1 - #30 triode, DETECTOR, Raytheon
V2 - #30 triode, AUDIO AMPLIFIER, Raytheon
PHONES - High impedance 3K ohms, Brandes "Superior Matched Tone"
L1 | Hammarlund XP-53, 5-pin coil forms, 1-1/2" diam.
L2 | 1/8" spacing between windings. L1 top, L2 middle, L3 bottom winding.
L3 | See Coil Chart below. All coils #28 AWG.

Coil Approx. Freq. Coverage L1 Turns L2 Turns L3 Turns
1 650 kHz - 1450 kHz 100 20 10
2 1200 kHz - 2.5 mHz 50 20 10
3 2.0 mHz - 4.2 mHz 20 10 7
4 3.8 mHz - 8.0 mHz 11 5 7
5 8.0 mHz - 15.5 mHz 4-1/2 5 5

List of References

The Hammarlund 1937 Short Wave Manual
Third Edition, Copyright 1935, Hammarlund Mfg. Co., Inc.
Reprinted by Lindsay Publications Inc.,
Box 12, Bradley, Illinois 60915

Short Wave Beginner's Book
Radio & Television, New York, N.Y., Copyright H. Gernsback, 1940
Reprinted by Lindsay Publications Inc.,
Box 12, Bradley, Illinois 60915

Short Wave Coil Data Book
Radio Publications, New York, Copyright H. Gernsback, 1937
Reprinted by Lindsay Publications Inc.,
Box 12, Bradley, Illinois 60915


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