1924 Browning Drake Reciever

Home - Valve Radios - Edisons - Phonographs - Browning Drake - Test Equipment

Building the Browning Drake Receiver by Jim Lowe

I was quite thrilled to be informed that I had won the postal section of the Historical Radio Society of Australia (HRSA) Browning-Drake Competition. For the information of others I will set out how I constructed the receiver.

Coils

The heart of the receiver is the two tuning coils. As it is rather difficult to obtain the double cotton covered wire originally used I substituted modern enamel wire. The problem here is that the spacing of the cotton covering makes the wire overall diameter greater .This changes the distributed capacitance of the coil. To overcome this problem I cut a groove in the coil formers on my lathe to a pitch of 0.75 mm (a pitch of 36 TPI could also have done). To do this I made up two tapered mandrels from wood and lightly pressed these into each end of the former. One was centred and the other held in the chuck. Then, after checking for concentricity, I cut a shallow spiral groove, the length of the winding, on the surface of the former. I drilled 0.8 mm holes at the beginning, tapping and end of the winding. I then wound the wire on with the lathe still set to the same pitch as the groove. As the wire is 0.63 mm diameter this gave me a spacing of 0.06 mm between turns. This would have been the thickness of the old double cotton insulation. As the seven AM stations in my area are up to 1629 kHz, and none below 981 kHz, I left 8 turns off each coil.

For the regenaformer primary winding I turned a ring from ¼" perspex with a 0.5 mm groove in the outer edge. Into this groove was wound the winding. The ring just pressed into the coil former and was positioned level with the bottom of the secondary winding. The tickler coil was made a smaller diameter in a similar manner but I glued two pieces of perspex together. This then gave room for the ¼" shaft to pass through with half the winding each side of the shaft. The nuts and bearings of two old wire-wound pots were fitted to each side of the coil former. The flexible leads to each end of the tickler were made from desoldering wick. This is ideal as it is very flexible yet strong.

Tuning Capacitors

As I had them on hand I used two 350 pF variable capacitors. They are of different make but both exhibit the same maximum and minimum capacitance. One is an Australian made ‘Advance’ with a boomerang symbol and the other is a US origin ‘Certified’ brand.

Dials

Here I was lucky enough to have on hand two slow-motion friction dials. These had been in my ‘junk box’ for the past 40 years! The original celluloid dials were beyond redemption so I drew up two new ones using my computer CAD programme and had them laminated. These were then fitted into the Bakelite housings. The two dials are of 1924 vintage so are in keeping with the style of the design. One had a knob but the other’s knob was missing. They were both fitted with the same old style knobs used for all the other controls on the front panel. This gave a nice uniformity to the panel.

Front Panel

This was made from 6 mm Formica supplied by Brian Smith of Rockhampton. I drew out the engraving for the front panel twice full size on paper. I used the same style lettering for ‘Browning-Drake’ as shown in old advertisements. This was then taken to a machine engraver who scanned my drawing and then engraved and filled the lettering. I was overjoyed with the result as it looked really professional.

Audio Transformers

I had a number of old coupling transformers on hand but decided to use two AWA types. These were originally painted ‘gold’ so I cleaned and resprayed them the same colour, then finished them with a clear top coat. They both have a turns ratio of 1:3. One was centre-tapped but I just ignored the centre tap. Magnetic field pick-up is a problem with coupling transformers so they were mounted mutually at 90 degrees. It also pays to keep power transformers well away from coupling transformers.

Mica Capacitors

Also, from my ‘junk box’, I had on hand a number of mica capacitors made by Foreman & Company of New York. These were way off nominated capacitance and were also very leaky. I cheated here by dismantling them and fitting modern mica capacitors inside the original housing. I then made up labels on my computer in exactly the same style, and colour, as the original and pasted these about the, now excellent, ‘new’ capacitors.

Grid leak

After much experimentation I found that 3 megohms seemed to give the best reception with the valves I used and my 5 metre indoor aerial. I had a box of old glass encased grid leaks but they were all over the place in resistance. I eventually found a number with resistances ranging from approximately 0.5 megohm to 7megohms that seemed stable. I again made up diamond shape paper labels, exactly the style and colour as the original, and pasted these on the glass. Again from the trusty ‘junk box’ I found a packet of grid-leak clips. These were polished and fitted to a ‘Foreman’ capacitor and really looked the part.

Valves

I had a number of old valves on hand that would have suited (99, 201 etc.) But did not have enough of the same type to fill all the sockets. I eventually settled on all Philips valves and used A415s and a B405 for the output. I had two B405s and decided to check the emission of each. I just put them in a socket put 135 volts on the anode and adjusted the bias while checking the anode current. One was way down while the other looked good. With the same set up I obtained the data from the good one to draw up a family of curves. From this graph I deduced that a bias voltage of -18 volts and a load resistance of 3,000 ohms would be ideal.

Since operating the receiver I am of the opinion that a filament rheostat in each of the valve’s filament circuits would be the better way to go. I followed the published recommendation and just used one for the RF stage and another for the detector and AF stages. I called these RF and AF gain but better performance would certainly result if each stage could be adjusted separately. It would make the operation rather daunting for anyone not technically minded but once adjusted usually the RF and output rheostats would be the only ones to alter.

Neutralising Capacitor

This is one item that is not really ‘old’. It looks the part but is a (1940s) RCS type with a maximum capacitance of 60 pF. It is a little large but I can get neutralisation with the plates almost all out. Correct neutralisation makes a world of difference. The regeneration can be advanced too far and all you get is a ‘click’ and reduced volume, plus a little distortion. At optimum feedback the sensitivity and selectivity are excellent. In fact selectivity is better than some older superhets I have restored. The stations in my area are very closely spaced for an old receiver.

Cabinet

This is my pèice de résistance. I made the cabinet from solid red cedar (Toomis Australis). I have had some red cedar planks, which once belonged to my father who passed on some 30 years ago. From these I made the cabinet, with a cedar veneered ply for the back, following strictly to the published photographs and drawings. I looked at as many photos as I could of mid 1920s style cabinets and most were of the fairly plain style. With this in mind a stuck to a classically simple design.

I filled the finished cedar with a mixture of mahogany and cedar fillers and then sprayed the rubbed-down surface with tree coats of nitrocellulose lacquer. I was very pleased with the results and there have been ‘oohs’ and ‘ahs’ from many who have viewed it. I cut an opening in the ply back so I could gain access to the 8 battery and aerial and earth binding posts. The binding posts were turned up by Terry Poole, of Lower Barrington, Tasmania and I had them nickel plated.

Power Supply

Unless we could buy, and afford, three large 45 volt B batteries, a two cell A accumulator and two 9 volt tapped C batteries there must be a proper power supply.

For the filament supply I used a 6.3 volt transformer and an adjustable voltage regulator. In the lower leg I used a variable resistor so I could adjust the voltage exactly. When I first used the receiver I had the voltage set to 4 volts. However, after a while I reduced it to 3.2 volts and obtained much better control of the receiver.

The two other supplies just use simple voltage dividers. For the bias supply I used an 18 volt transformer and rectified and filtered the output. I passed about 10 mA through a voltage divider and as the bias supply draws virtually zero current the voltage remains constant.

The B supply always poses a problem as the transformers, unless specially manufactured, are not normally obtainable. I got over this by winding my own. I purchased from Brian Smith, of Rockhampton, a set of laminations, a bobbin and a cover. I then wound on the bobbin 2400 turns of 0.15 mm wire for the primary, wrapped around good insulation and then added 950 turns of 0.25 mm wire for the secondary. I made the complete transformer in about 45 minutes. I wound it on my lathe with a revolution counter attached. The output of this when rectified and filtered gives me very close to 135 volts. This goes straight to the output stage and also to a voltage divider which gives me 90, 68 and 22 volts, approximately, for the other stages of the receiver. The voltage divider passes about 10 mA and as the anode current for the first three valves is minimal the voltages are relatively constant. This approach may be frowned on by some but it is simple, reliable, easy to get going and cheap.

Speaker

From the dim recesses of my junk room I unearthed a 1924 ‘Gecaphone’ diaphragm-horn speaker. This was rather decrepit so I pulled it apart, checked the windings and cleaned it up and

spray painted it. It has an intriguing multi-start thread mechanism to raise and lower the magnet pole pieces from the diaphragm. This acts as a ‘volume control’. It was seized but penetrating oil eventually freed it up.

The speaker has a winding on each pole brought out to separate terminals. Each of these is 1500 ohms so connecting them in series gave me exactly the 3,000 ohms I needed to match the output valve. I had not tested the receiver before I hooked up the power supplies and the speaker and was both delighted, and amazed, when it burst into life. I felt like Thomas Edison who once said, "I am always scared of things that work the first time." How does it sound? Well, similar to old horn gramophones and certainly not Hi Fi but it is representative of the sound produced by the original Browning-Drake radios of those days and aren’t we looking for authenticity?

Conclusion

I am delighted with my Browning-Drake receiver as it is really more than I expected. It does prove to me, though, that we have come a long way in radio electronics. No one would fiddle with five separate controls to tune between two stations and no one would put up with the sound from the old speaker. However, to me it is a joy to behold and is now the favourite in my collection.

Browning-Drake Power Supply

Due to the cost, size and availability of batteries to power this unit I decided to make a Battery Eliminator as shown below. I have included the circuit diagrams and front panel layout.

Front Panel Layout

Circuit Diagrams

Home