[Boatanchors] Japanese WW II Code practice oscillators

[William L Howard]

I have been discussing Japanese WW II code practice oscillators with the
seller of the set now up for sale. The Japanese Navy Code practice
oscillator runs from either AC or DC, has two tubes, one a rectifier
tube and the other I assume is an oscillator. The Army version is
battery powered, has one tube and a variable capacitor. The question was
"Why have a variable capacitor in code oscillator?"

Now remember this is 1920s state of the art so can anyone make a
suggestion as to why the variable capacitor?
Pictures of both sets can be found on my web site article on Japanese
radios.

Thanks,

Bill Howard
William L. Howard Ordnance Technical Intelligence Museum
wlhoward at verizon.net  Web Site www.wlhoward.com Phone: 727-585-7756