The first step in building this or any project is getting the parts. In fact, this may be the most difficult step. When it comes to building a replica of an old radio like this, you just cannot go out and buy everything you need. You may have to adapt and use whatever you have on hand or can scavenge. For a project of this type you may want to build the circuit using point-to-point wiring between terminal and components rather than a circuit board to give the radio an “old-time” look. You are probably going to need both a soldering iron and a soldering gun to build this radio. You will also want to consult with the resistor color code chart in Table 7-1 and the capacitor code chart in Table 7-2 in order to identify the correct components.
Building this old radio can be lots of fun, but locating all of these old components can be difficult, and in fact you won’t be able to locate the exact same items. You’ll
get something close. You’ll have to mix and match whatever you can find. Most of these components are available at flea markets if you visit enough of them. Many of the components are available new from dealers, such as Antique Radio Supply, see Appendix. But often you’ll have to pay substantially higher yet fair prices. The used #19 tube was purchased from a flea market dealer for $5. Yet, that same tube can be obtained brand new from Antique Electronic Supply for about $6, see Appendix. Again, you may have to scrounge, make do, adapt, experiment, and make a few mistakes. But the results are well worth it.
One idea is to build a prototype receiver with whatever components you can find, no matter how new or old, and get it working. Then, over the next few years, visit flea markets, antique radio meets, check out dealers’ catalogs, and accumulate the older, more authentic parts. After you accumulate some of those rare, old, beautiful parts from the 20% and 30%, rebuild the receiver. And then a few years later rebuild it again. And every time you rebuild it, add older and more authentic parts, until you get an exact copy of the #19 Doerle receiver. The radio will become more and more of an authentic replica of a receiver from the early days of radio. With patience, practice, and plenty of enjoyment, you can build a fine radio.
Looking at the illustration of the Doerle-1 version, we see in the center a large, slow-motion dial drive
Table 7-1
Resistor color code chart
Color Band 1st Digit 2nd Digit Multiplier Tolerance
Black 0 0 1 Brown 1 1 10 1% Red 2 2 100 2% Orange 3 3 1,000 (K) 3% Yellow 4 4 10,000 4% Green 5 5 100,000 Blue 6 6 1,000,000 (M) Violet 7 7 10,000,000 Gray 8 8 100,000,000 White 9 9 1,000,000,000 Gold 0.1 5% Silver 0.01 10% No color 20%
Chapter Seven: Super-Regenerative Radio Receiver
Table 7-2
Capacitance code information
This table provides the value of alphanumeric coded ceramic, mylar and mica capacitors in general. They come in many sizes, shapes, values and ratings; many different manufacturers worldwide produce them and not all play by the same rules. Some capacitors actually have the numeric values stamped on them; however, many are color coded and some have alphanumeric codes. The capacitor’s first and second significant number IDs are the first and second values, followed by the multiplier number code, followed by the percentage tolerance letter code. Usually the first two digits of the code represent the significant part of the value, while the third digit, called the multiplier, corresponds to the number of zeros to be added to the first two digits.
Value Type Code Value Type Code
1.5 pF Ceramic 1,000 pF /.001µF Ceramic / Mylar 102 3.3 pF Ceramic 1,500 pF /.0015µF Ceramic / Mylar 152 10 pF Ceramic 2,000 pF /.002µF Ceramic / Mylar 202 15 pF Ceramic 2,200 pF /.0022µF Ceramic / Mylar 222 20 pF Ceramic 4,700 pF /.0047µF Ceramic / Mylar 472 30 pF Ceramic 5,000 pF /.005µF Ceramic / Mylar 502 33 pF Ceramic 5,600 pF /.0056µF Ceramic / Mylar 562 47 pF Ceramic 6,800 pF /.0068µF Ceramic / Mylar 682 56 pF Ceramic .01 Ceramic / Mylar 103 68 pF Ceramic .015 Mylar 75 pF Ceramic .02 Mylar 203 82 pF Ceramic .022 Mylar 223 91 pF Ceramic .033 Mylar 333 100 pF Ceramic 101 .047 Mylar 473 120 pF Ceramic 121 .05 Mylar 503 130 pF Ceramic 131 .056 Mylar 563 150 pF Ceramic 151 .068 Mylar 683 180 pF Ceramic 181 .1 Mylar 104 220 pF Ceramic 221 .2 Mylar 204 330 pF Ceramic 331 .22 Mylar 224 470 pF Ceramic 471 .33 Mylar 334 560 pF Ceramic 561 .47 Mylar 474 680 pF Ceramic 681 .56 Mylar 564 750 pF Ceramic 751 1 Mylar 105 820 pF Ceramic 821 2 Mylar 205 1st Significant Figure 2nd Significant Figure Multiplier Tolerance CSGNetwork.Com 6/4/92 0.1µF 10% 104 k
friction-driven by a small knob at the bottom of the set. This allows fine tuning of stations. To the upper left are the antenna and ground terminals. Just to the right in a hole in the front panel is exposed the screw which adjusts the antenna coupling capacitor. Below left is the filament rheostat knob. At the upper right are the headphone terminals with the regeneration control located at the lower right. Although the receiver as shown in the original drawings may appear complex, it really is not. This is one of simplest receivers that you could build.
The original chassis for the Doerle receiver was an L-shaped piece of sheet metal, most likely steel, and painted with a black wrinkle finish. While the front panel was perfectly rectangular, the base was
trapezoidal. Dimples were embossed into the base plate which served as feet.
For our replica Doerle receiver, you can start with an 11′′ ×9′′sheet of .063′′(1⁄
16′′) aluminum to construct the
chassis. The most complicated mechanical problems that you may encounter in building the receiver is the mounting #19 dual triode tube up on standoffs, mounting the variable capacitors and building the coils on the coil-form, see Figure 7-4.
The original Doerle model used a simple single bearing variable capacitor. We elected to use a heavy duty Hammarlund tuning capacitor; it is of significantly higher quality and is much heavier, so you will have to support the rear end of the capacitor with a bracket of some type. Once a Z-bracket as fabricated and attached to the breadboard, the prototype dial-drive-capacitor assembly was solid, yet turned smoothly.
Since a solid, rigid mount for the tuning capacitor is essential if you are to achieve frequency stability and eliminate microphonics, you must get this part of the assembly correct. And since your components will need their own custom mounting hardware, you’ll need to experiment until you get it right. That’s why the breadboard prototype is so useful. Take your time.
In continuing the capacitor assembly, I used a pair of 1⁄ 2′′
long 6-32 machine screws in the top and bottom pair of holes on the drive mechanism. In the left-right pair of holes, I used a pair of 11⁄
2′′long 6-32 machine screws.
The extra length became mounting studs to which an aluminum cross-arm was attached. In the cross-arm was drilled a 3⁄
8′′hole to accommodate the mounting flange
of the capacitor.
After the capacitor holes were drilled, the burrs removed, and edges of the panel were rounded and smoothed, I roughed up the surface with fine sandpaper.
Table 7-3
Short-wave band listening frequencies
Shortwave Band Shortwave Band
120 meters =2300–2495 kHz 25 meters =11.500–12.160 MHz 90 meters =3200–3400 kHz 22 meters =13.570–13.870 MHz 75 meters =3900–4000 kHz 19 meters =15.030–15.800 MHz 60 meters =4750–5060 kHz 17 meters =17.480–17.900 MHz 49 meters =5730–6295 kHz 16 meters =18.900–19.020 MHz 41 meters =6890–6990 kHz 13 meters =21.450–21.750 MHz 41 meters =7100–7600 kHz 11 meters =25.670–26.100 MHz 31 meters =9250–9990 kHz
Figure 7-4 Doerle coil assembly
Chapter Seven: Super-Regenerative Radio Receiver
Next, the panel was bent into an L shape. You can use an old sheet metal brake, or you can could do the same by clamping the metal between a couple of 1 by 2’s or lengths of angle iron held tightly together in a vise or with C-clamps. Since only a single, simple bend is required, you might get by clamping the sheet metal to a table top and by bending the sheet over the edge.
In order to obtain smooth tuning with a large range, you should locate some sort of planetary drive mechanism in front of the main tuning capacitor, such as a used National Velvet Vernier dial drive, which can be removed from an old radio. The first step was to dismantle it into the drive mechanism, the knob, and the dial plate. To mount the actual planetary drive
mechanism, I had to cut a 5⁄
8′′hole in the plate with a
socket punch. Next, the drive collar was slipped through the5⁄
8′′hole. With a marker I marked the location of the
four mounting holes.
In moving the capacitor and dial drive to the finished receiver, I chose to position the angle mounting bracket vertically as shown in the photos. This made fabrication and installation of a new base bracket much easier, and allowed more clearance for the tube and coil socket as well as for the terminal strip below the dial drive.
When the components are “test” mounted, you can move from the prototype stage to the finished L-shaped panel, if you are happy with the final layout. Then you can spray on a thick coat of fast drying metal primer. Once dry, I wet-sanded it under a stream of water until smooth. Then came the black wrinkle paint. If you wish to try and duplicate the original, you will want to try and create the wrinkle finish. If you are not that concerned about having the radio look exactly like the original radio, you can just paint the chassis with a single coat of black paint. Black Krylon paint is available in a spray can in your local home
improvement store. For best results in creating a wrinkle finish, you must put down a heavy layer of paint. It must be heavy so that it can wrinkle up as it dries. If the coat is too light, or if you try to apply a second light coat over the existing layer, you won’t get the best results. It might even be shiny where it is supposed to be flat black.
It is recommended that you paint one surface at a time and let it dry. Then reposition the chassis so that another surface is horizontal and then paint that. Of course, it will take four times as long to paint the radio
than if you get in a hurry and paint the whole thing at once, but the results will be more predictable. You can bake it in an electric kitchen oven at the lowest possible heat. Nasty smelling solvents are baked out of the paint, so your wife or mother may not be too happy with you!
After mounting the tuning capacitor, the only other assembly of any complexity is the coil socket and antenna trimmer mount. Mounting the other components was fairly easily done. You can use
machine screws, spacers of wood, plastic, porcelain, and metal. You can slice wood spacers from hardwood planks, but you’ll need a table saw to do a good job. Plastic spacers can be cut from plastic tubing, but just be sure to get the rigid stuff used by plumbers for water supply lines. Porcelain spacers are something, which can be scavenged at a local hamfest or radio flea market. A small trimmer capacitor is mounted on porcelain standoffs in order to insulate both terminals from the chassis. Between the standoffs is a drilled 3⁄
8′′hole in the
front panel to allow screwdriver adjustment. That sounds simple enough. But behind the trimmer is the socket that accepts the four-pin lube socket coil form. What I used here were a couple of 2′′6-32 machine screws cut to the appropriate length with heavy clippers. They were then fed through the coil socket mounting holes and through brake line spacers into the porcelain standoffs. Two soldering lugs were sandwiched between each metal spacer and porcelain standoff. One lug on each side was soldered to a capacitor lead. The other lug on each side became connector for the trimmer. Since the metal spacer pressed tightly against the capacitor lead, it was imperative that the four pin socket be made of insulating material. Here I used an old phenolic wafer socket. A metal socket would short out the capacitor. It sounds complicated but it should be fairly easily understood by studying the photographs.
Wiring was done with some modern plastic covered hookup wire, and with some genuinely old cloth-covered hookup wire salvaged from a piece of old tube gear. Watch for old tube gear with long lengths of cloth-covered wiring at flea markets. New old stock cloth covered wire is around but it is not always easy to find. Sometimes you can look for old wire while scavenging at hamfests.
The coils used in the original circuit were 11⁄
2′′dia. by
3′′tall phenolic coil forms. You can use phenolic bases from four prong tubes for the coil forms and they can be
purchased from Antique Electronic Supply. The low frequency or main “short-wave” coil is close-wound with about 30 turns of #26 wire. You wind the “tickler” coil, which is 9 or10 turns of #24 ga. wire below the tuning coil, and both coils were covered with clear fingernail polish. The coil covers approximately 2.5 to 4.5 MHz. The exact number of turns you’ll need is going to depend on the tuning capacitor you use and the stray capacitance that results from your particular component layout, among other things. You’ll have to experiment to get the right number of turns.
The original Dorele receiver had plug-in coils for different radio bands. In order to construct an AM radio coil, you will have to wind another main coil along with another “tickler” coil on a second coil form. The main coil will need about 40 turns of #26 ga. wire, with a 9–10 turn “tickler” winding.
Battery terminals can also be purchased at a radio flea market. Using a table saw you could elect to slice a 1⁄
4′′
strip from an oak 1×6. That gave me a mounting strip of
3⁄
4′′ ×51⁄2′′ ×1⁄41′′thick, just right for this radio.