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Above are pictures of the original Mark III ("Tinker Box") located at Station X, in Bletchley Park. This Transmitter and an HRO Receiver, was used to communicate with Parasets in the field . Although over 100 were made for various embassies, There were only four known units in existence, and no known schematics.
These pictures show the replica of the Mark III that I made. I used a series of schematics from the late 1930's. If there are any differences they are minor in nature and I was unaware when I built the unit. That said , I maintained the MOPA circuit and used the 6V6 807 concept.
I am constructing a replica of Station X located at Bletchley Park in the UK. These photos show the HRO receiver and the Mark III Transmitter. In front of the HRO are the stand-off spreaders. These will go across the wall and ceiling of the shack.
This is the original schematic Drawn by David White Curator of Station X at Bletchley park, UK. There are a couple of anomalies in the drawing, but I believe Mr. White was working under a time restraint and had one evening to disassemble the set and put everything on paper.
This is the circuit I devised. I have eliminated the "HOT variable caps, changed the screen supply and changed the simple crystal oscillator to a Colpitts design. I used the Colpitts design because it tended to be more stable with less chirp at higher frequencies.
This Adobe file contains all the data you need to construct a Mark III Tinker Box. This is NOT a step by step construction article, but I will field any and all questions you mat have on building the radio. Be advised this IS NOT like the article in the January issue of QST. I built my Mark III approximately the same time they built theirs and we were not in contact at the time. This as in all tube type projects, Have lethal voltages present and all safety precautions should be observed.