Collaboration "Like-A-Flash"     by DanPetersen, WA6OIL

                                                                                         Mike Peebles & David Walshaw

This is the story of a project that was truly international in scope and has had an influence on global affairs. Well…maybe that sounds a little high-falutin’ for a collaboration between two Yanks and an Aussie in the construction of a crystal set but it is true nonetheless. As I go along I will detail the construction of a set that is a real “ripper”.

This all started last (northern hemisphere) summer when I made a reply to an Australian by the name of David Walshaw to complement him on his work. He replied and soon we were exchanging daily messages. Soon I let my good friend Mike Peebles in on the deal as David was supplying me with some really good information from Australian and British sources. So the three of us made fast friends and that is when David told us about the “Levinson Like-A-Flash” sets that he had articles on.

Levinson’s Radio of Pitt Street, Sydney, Australia was a supplier of “Games, Hobbies and Coin-operated machines” as well as a line of finished radios, kits and parts.  Levinson’s wrote a series of booklets concerning their radio gear and of course was more than happy to sell any parts needed for their construction.

The three of us decided to build Levinson’s “Like-A-Flash” (LAF) set and to compare notes on how they performed. Since there were several to choose from we settled on the “Senior” model. Each of us would have the same information on the LAF Senior and could “do their own thing” in building it.

Mike decided to build his set in both the two-circuit type shown in the booklet and a single tuning control model where the antenna and detector tuning are ganged. David and I opted for the more “classic” look of the original unit and would build only the two-circuit version. I wished to be as authentic as possible so I asked David if he could round up a matched pair of Aussie tuning capacitors. After some “serious” horse-trading, I sent him the gear he wanted and he sent me those two capacitors and three more of different styles to boot. Fair warning: If you want to get into this type of Trans-Pacific stuff, shipping can be pretty stiff. When I sent my last shipment to David, I paid the postage and two postal employees retired on the spot!

The Radio: The Like-A-Flash Senior is an interesting yet fairly straightforward circuit. It employs two coils, one for antenna tuning and the other for detector tuning. An interesting feature of this set is that the two coils are mounted at right angles to one another and part of the antenna tuning coil’s inductance is on the detector coil. The antenna has four taps that lead to a switch that switches the antenna to any one of the taps. The detector coil is center-tapped for the detector circuit.

Figure one shows the wiring diagram for the “LAF” Senior. In keeping with the desire to make as an “original” set as possible I had to fudge on a couple of things. I couldn’t find appropriate diameter coil forms so I made them out of thin wood veneer with plywood rings at each end to strengthen them. Once made, I painted them black then wound them with #20 (0.87mm) enameled wire. Cotton covered wire would be more authentic but I didn’t have enough handy.  I then applied a coat of varnish to hold the turns to the coil-form.

In my version, L1 consists of 42 turns of #20 (0.87mm) enameled wire on a 2-3/4” (70mm) diameter form 3” (75mm)in length. L1's aerial taps are at 5, 10, 15 and 20 turns from the end that connects to L3. L2 is 67 turns of #20 (0.87mm) enameled wire on another 2-3/4” (70mm) diameter form 4” (100mm) in length and is center-tapped. L3 is 15 turns of #20 (0.87mm) enameled wire wound on L2’s form spaced ¼” (6mm) from L2. The two coil forms are mounted to the board at right angles to one another. This is important, as the coils must not inductively couple with one another except through L3. In this circuit, transfer of the signal from L1 to L2 is done by L3, which is electrically in series with L1 but is inductively coupled to L2. This is a neat bit of electrical trickery to minimize the number of parts needed while still getting the job done.

Figure 2 shows the general layout. As per the original instructions, I used a 6” (150mm) by 12” (300mm) piece of ¾” (19mm) pine to build the set on and a 6” (150mm) by 12” (300mm) piece of 1/8” (3mm) thick black bakelite for the front panel. Other materials can be used of course as long as they are non-conductive. Except for the coils, layout is not critical nor is lead length.

The purist (like me) will want to use original tuning capacitors. This set will work just as well with the 365pF variable capacitors sold by the Xtal Set  Society. As stated before, I was able to procure two matched authentic Aussie variables for my set. The tuning knobs on my set are also matched. I found them at a ham radio fleamarket. For the new people on the block, ham radio fleamarkets are a goldmine for old parts. Obtain the latest QST  magazine (subscription, a friend or the local library) for dates and locations of fleamarkets and hamfairs.

The aerial tap switch is homebrew. A hobby shop supplies brass strips in different widths and thicknesses. A piece ¼” (6mm) wide and 1/16” (1.5mm) thick is ideal for making the switch lever. As seen in the photo, the switch studs are made from 8-32 (4mm) round-head screws used to fasten the glass covers to ceiling light fixtures. The center pivot consists of a screw going through the front panel, then a washer and nut is used to tighten it down to the panel. The switch lever is set on the screw, then a washer, a spring, then another washer. I use a knurled nut to tighten the whole shebang down. The spring should be small but stout. You should not be able to pinch it down all the way with your fingers.

You may use a vintage style detector stand or opt for the more modern diode. A 1N34 (US) or an OA91 (rest of the planet) will work fine. With this unit, I can use either the diode or stand. I clip a diode across the detector stand terminals and pull the cat-whisker away from the galena. For a more realistic (read “hair-pulling”) experience, use a detector stand. (Hey-ya! Hey-ya! Hey-ya!. “Step right up and test your patience! Make the radio work and the little lady wins a teddy-bear!”) Actually, I find that a well-adjusted detector stand will give a germanium diode a run for its money – that is until you drop something on the table or the temperature changes or any of a hundred other things happen. They are a might touchy to use.

Performance: So far I have done a pretty good job at leaving the other two guys out. The three of us live in three widely differing RF environments. I live in a rural setting with lots of room for big antennas and no nearby powerhouses. David lives on an urban-sized lot in a small town in South Australia with a couple of stations available during the day, neither of them overpowering. Mike lives near two 50,000 watt stations that compete to see which one can turn on his fluorescent lights with their RF energy. So although our sets are physically different, they are electrically similar.

From David Walshaw in Australia

"In regards to the LAF, I can get 2 local stations really well here and at nights I can hear an Adelaide Station some 400km's away.

The set is very easy to use, I find a very faint station then use the combination of selector switch and aerial tuner to bring it in stronger. I have about a hundred feet (thirty metres) of stranded copper wire up and about 20 feet (6m)in the air, I have recently redone my earth to include the cold water plumbing of the house and that seems to work much better although it does not appear to be as good as the one in the original configuration when I was in the back shed. I suspect it is a combination of aerial orientation and earth. The limestone is probably not as good a conductor as it should be. The ABC on 890 really booms in but 5SE on 961 even though the transmitter is 49 kilometres away is difficult to tune. I understand that where I am there is a null with the direction of the transmitting aerial. I am very impressed with the set, I use an IN34A and low impedance (540 ohm) headphones with a matching transformer that takes them out to 2000 ohm."

Mike Peebles writes:

"I decided to build two of these sets, one with a dual gang/single tuning knob and another with two separate tuning knobs for the antenna and detector stages. I also modified the circuits of each (see schematics) and found these circuits to work best in my location. The set with two separate tuning controls was naturally the best performer and I knew it would, but was curious to see how well the single knob set would compare.

The two-knob set was able to pull-in 7 separate stations without changing the antenna tuner. The antenna tuner was set to peak at 620 kHz. If I changed the antenna tuner as I progressed-up, towards 1700 kHz from the low-end of the band, I was able to denote an audible clarity for a count of 12 separate stations. Two 50,000-watt stations at 860 and 1550 are difficult to deal with, in the "selectivity" area, so I considered the above results quite good. Did not denote any DX, and was not looking for it, as selectivity was my main experiment here.

The one-knob set was not as great as the above set, but not disappointing. The set pulled-in 5 separate stations without changing the antenna tuner and 9 with progressing the antenna tuner accordingly. In conclusion: the sets were fun and of course look great in my collection, but most of all was able to share the experience with three people across the world. Marconi and Edison would be proud!"

As for Myself:

My Like-A-Flash Senior set is probably the best performer of any in my collection of sets. The antenna tap and antenna tuning are a great help in nailing down stations. The DX performance is impressive. I live about 25 miles north of Portland, Oregon. Nightly I can pick up KGO in San Francisco, a distance of over 500 miles (800km). It can come in louder than the locals on a good night. Another station at about the same distance that I hear nightly is KFBK in Sacramento. I have also picked up XEPRS in Mexico at a distance of 1100 (1770km) miles. I use a 200 foot (60m) antenna 30 feet (10m) above the ground and an 8 foot (2.5m)ground rod for a ground connection. During the day I can easily separate about a dozen local outlets. The tuning covers the broadcast band very nicely. There is of course a certain amount of tuning interaction between the two tuning controls but it is not as bad as on my "It Came From the Junkbox" which was featured in another article in the XSS newsletter.

The photos above really do not do any of these sets any justice. If you wish for better shots, visit my website at http://www.worldaccessnet.com/~petersen. By the time this is published, I will have a section with color photos that you can see and download. As always, if you have any questions or comments, you can e-mail me at petersen@worldaccessnet.com .

This was a fun collaboration. The power of the internet is immense and the opportunities for international communications and cooperation is practically unlimited. As David Walshaw likes to quote, "People rarely succeed unless they have fun doing it". This has been a ball.

-Dan Petersen-