[Milsurplus] Ideas on Japanese circuit ?

[Hubert Miller]

There is a switch built onto the BFO varicap that shorts the BFO and turns on the audio
oscillator. So my assumption is that this a species of BFO systems, maybe to deal with 
noise or drifty frequency of the sending station. The detector looks to me like biased
to delayed AVC. There is a separate detector take off for audio. 
I looked at the hard copy last night and there's providentially a board with 16 measuring
points with the specified voltage marked at each terminal. That is a great help cuz it 
identifies the B+ as 250, along with all the screen voltages and the G1 bias. There is one
voltage identified as -63 volts. I don't know what that is about; maybe it is transferred to
the transmitter. The receive tube bias is something like in the RU receiver where you have
a voltage drop thru a resistor and the tube grids are "below ground". There's a -8 volt 
measuring point on this board and i so far assume that's the resting grid voltage. I need
to do some consulting of the tube books for the 6F7. Another thing interesting to me is that 
the design seems to be usable for either - or + aircraft frame. The overall construction is
something you could be quite proud of in maybe 1937, not much later. This radio, the 99-1
designation, the 99 means Japan year 2539, our year 1939. Most of their military equipment
seems to date to this period when the country was rapidly up-arming. I am going to take 
some closeup shots of various markings and try to get a translation. But even lacking that,
i think i am understanding enough that this project seems likely to have a good outcome.
-Hue Miller