One recent project was building a replica of the “canteen radio” that was used by US Army personnel in the Japanese POW camp at Cabanatuan in the Philippines during WWII. Its layout follows a description and drawing published in the Reference (5): US Army in WWII, The Technical Services, The Signal Corps: The Outcome pp 274-275. This prototype is very sensitive – using a 6SK7 or 12SK7 it can receive many foreign shortwave broadcasts from about 3.8 – 7.5 MC, using a 50 foot wire antenna. Their antenna was woven inside a clothesline. The radio escaped discovery by the Japanese guards until the camp was assaulted and liberated on 30 JAN, 1945. Assault personnel were from Company C and F, 6th Ranger Battalion, Alamo scouts and Filipino guerillas.
My replica radio will operate with B+ as low as 24 volts but I usually run it at 63 VDC provided by seven, 9 V batteries. They simulate my 67.5 V dry cell that has failed long ago. The POW camp captives made batteries from bits of copper and zinc uniform buttons and battery acid captured from enemy vehicle batteries. Reference (12).
Here’s a look at the innards. The bamboo coil form is evident,the winding job is embarrassing.
The Signal Corps of WWII had many men who were “Ham” radio operators before the war and the design of this type of radio would have been memorized long before – it was a basic, common design. No instructions needed by skilled personnel. The radio was built by Capt. Russell J. Hutchinson, US Army Engineer Corps and subsequently passed to William D Gibson, a Ham radio operator and Signal Corps Lieutenant.
This replica is made from primarily WWII vintage electronic parts and includes 2 tuning coils wound on 1 inch diameter bamboo forms. One is for SW broadcasts, the other for broadcast band use; the turns are held in place with pine pitch. The four D cell filament batteries are appropriately concealed inside a piece of bamboo tube. (Mine uses a 6SK7 because I couldn’t fit 8 D Cells inside the bamboo tube to power the 12 volt filaments of a 12SK7.) It is my first attempt at building a one-tube regenerative receiver and it works pretty well on AM and CW. SSB reception (these days) is dependent upon careful adjustment and your imagination – SSB stability isn’t great but theirs brought in the AM news from BBC, Radio Australia and US west coast stations including KGEI in San Francisco. Much more fun to play with than a “software defined radio”. Theirs was a courage and ingenuity – defined radio.
So, does it really work? Yes, surprisingly well on AM shortwave. Like all Regens, careful adjustment of the Regeneration control is important and all the controls interact with each other to a certain extent. The Regen control varies the screen voltage and therefore the gain. The tuned circuit is isolated from the antenna by a series variable “antenna” capacitor which reduced the detuning effect of the antenna on the tuned circuit. If the wind is blowing the antenna around, the circuit detunes a bit and you have to compensate, but that is a minor problem. Selectivity is good, “tuning rate” via the screwdriver-trimmer is very fast but the Chicken Head fine tuning knob makes that acceptable. Moving the feedback tap on the tuning coil makes it ” a completely different radio”, something that can only be appreciated while experimenting with the construction and testing.
I can clearly hear WWV on 5 and 10 MC and occasionally CHU in Ottawa on 7850 KC. The big international SW stations come in pretty well. Considering the primitive nature of this radio, it does the job of providing outside contact as your imagination drifts back to the Philippines in WWII. The challenge was to see what kind of performance could be squeezed from some junk-box parts. Very satisfying project and a big hit with the public at displays and demonstrations.
There is speculation that the radio was actually originally built on Corregidor before its capture (Bataan death march to Cabanatuan) but was later modified in the camp for a 6J7 tube after the original 12SK7 tube burned out. Considering the parts requirements, this scenario rings true to me. It hung on the bunk of its custodian, in its canteen cup within the canvas cover – hidden in plain sight. The headphone(s) would have been hidden elsewhere. Its discovery would certainly have resulted in the summary murder of that American soldier, at a minimum.
Reference (11) notes that there was a second shortwave radio at Cabanatuan, built by prisoners with parts stolen from the enemy radio repair shop where some US personnel worked. They would capture the necessary parts from enemy radio equipment they were supposed to be repairing, telling their captors that parts had failed and replacement parts were needed. This radio was powered by the camp electrical lighting system which the prisoners had occasional access to. Brave, resourceful people.
As a telling fact, the United States GAVE radios to POW’s, at least to the Germans interred in the US. We were not afraid of them finding out what was going on. The Escape Factory, Reference (6).
Also, see Ray (VK2GRP)’s excellent website for a representative schematic and his fine reproduction radio as well (his pre-dates mine). Well done Ray ! www.tuberadio.com
This site is WAY cool! I need a canteen radio!