I have this project to put a Japanese IJA radio Type 99-1 back on the air, working.
( Special thanks to you-know-who-you-are for your invaluable help in acquiring this set !! )

I just this week discovered that i had a schematic for the thing, a schematic sent to

me years ago by Colonel William Howard. The schematic is small, crammed onto one

page, tiny lines, and the Japanese text characters are mostly illegible. Nevertheless,

having the schematic and not having to draw it out from scratch has lessened my

task to dozens of hours from hundreds of hours or, even infinite hours.

The circuit is: Transmitter, 2x 807 parallel power oscillator, quartz controlled. 807

screen modulator.  Receiver, 6x 6F7 ( Japan’s favorite tube, it seems ).  2x RF, mixer,

HF Osc, 2x IF, detector, AGC, first audio, pushpull audio output. The receiver dyno

has two sections; one delivers the low B+ and one delivers a negative bias voltage.

The power input is 6 volts DC, crazy as that seems. There seems to have been a

rheostat for finetuning the DC input voltage.

Both – and + legs of the 6 volt supply are actual separate cables to the battery. That’s

odd, isn’t it? I think all US aircraft used the frame of the aircraft as one power leg.

This thing may seem a little backward, compared to maybe our BC-307 BC-224-A from

1936, and the Navy’s GO and RAX equipment from 1940. However ‘99’ in the model

designation means Japan’s year 2599 = our year 1939, so it’s either up to USA technology

level or at most, very shortly behind, for the times.

-Hue Miller