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Building a replica of the B2 Mark III Spy Suitcase
- Created on 09 July 2010
- Last Updated on 30 October 2013
- Written by Administrator
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How it all started... Well, on February 7 2009 our radioclub payed a visit to the radio museum Jan Corver, at that time running an exhibition about secret radio's during WWII. In a corner of the museum was a B2, fully operational, and I had the opportunity to make a couple of QSO's with it. And then I was lost...
It was like being in the war myself - the B2 powered by a special adapter between the lightbulb and the fitting, a piece of wire running through the museum to the top of a tree outside. Though tuning was a bit itchy, audio was quite well. The set had a crystal at the dutch CW-frequency of 3.575kHz. I got nice reports, and the set worked remarkably well considering its age.
So I wanted one for myself. Beside the fact that a fine sample of the B2 is very rare, IF you ever find one it costs big money. In Googles cache I found a mint B2 selling for just over €8000. No way I'm going to spend that amount of money for a B2. It's for fun and using it, not for future investment and displaying it...
The alternative: Making one. Much information can be found on the internet, including the manual and schematics. The problem would be getting the right components - at least as genuine as possible. That's where the search started. First goal: find a suitcase. The dimensions were mentioned on the internet: 47x29x12cm. After a few weeks, I found a suitcase with exact those dimensions in a antiqueshop somewhere in the south of the Netherlands. Mission 1 completed: suitcase found...
The suitcase. Worn out enough to look original
The inside, some christmas decoration left...
I expected the valves to be a problem, but eventually I managed to buy the complete set on eBay. A EL32/VT52, a 6L6/VT115, 3 pcs 7R7 and 3 pcs 7Q7. Only 2 pieces 7R7 and 7Q7 are necessary; I keep the other ones as spare.
Complete set of valves for the B2.
The boxes look like theye are from a museum themselves...
A real 6L6 from 1944!
That's what a steel 6L6 looks like.
Besides the valves, many more components needed to be found. Eventually I managed to get a tuning knob with a 1:90 vernier. Ok, this is going to be different from the original. In the original B2 the tuning capacitor was driven by a string. Because of the 1:90 vernier, the tuning knob can drive the capacitor directly. Of course I need to find a way to drive the tuning indicator wheel also. Something to think about.
Tuning knob with 1:90 vernier dial: coarse with the outer ring, fine with the knob.
And then the search for a meter. I bought a 230V-230V safety transformer that had a meter build-in with a full scale of 300VAC. The size was just about right, so I took it apart and removed the internal rectifier and precision resistor. The meter had a sensitivity of 0.8333mA full scale. The original meter of the B2 is specified as 0.5mA. Close enough. It means some recalculation of the parallel/series resistors to get the right indication, but that is not really a big deal.
I also removed the meter scale and scanned it so I had a copy on the computer. With the magnification of some B2 pictures I photoshopped a good lookalike of the original meter scale:
The meter, as accurate as I could make it...
Time for the real work. Though I can handle a soldering iron pretty well, I really become dangerous when handling other tools - especially for myself. I already start bleeding when looking at a saw - so special troops were needed here. Fortunately, Mans PA2HGJ has access to the mechanical workshop of a large hospital and on a sunday we were allowed to use the workshop. Though 3 of the 4 units in the suitcase are merely a lid on a box, the powersupply is a bit more complicated, because it has a sunk part where the switch, fuses and connectors are located. Plus a frame to support the transformer. Everything starts with a good plan, in this case a drawing:
Drawing of the powersupply hardware
And because of my clumsiness, some members of our radioclub offered to help me.
Mans PA2HGJ (left) and Hugo PA2HW cutting 1.5mm sheets of aluminium
Frank PA3CNO (left), Mans PA2HGJ and Hugo PA2HW bending the chassis
The first lid is finished!
All hardware prepared: spares box lid, RX and TX front, power supply chassis
The search for parts continues, but now it is time to start building the power supply.