[Milsurplus] BC-474, more

[Hubert Miller]

Looking at the BC-474 schematics, i realized that with a single B+ supply for rec and trans, I did not really need to add a zener to the homebuilt
supply i acquired, AS LONG AS the supply B- goes to the transmitter B- connector and not to the chassis. Something like tri-state logic :

  1.  In In transmit, the receiver B+ is opened ( S8 #6 ) so there's no problem with lack of a -bias voltage. The transmitter circuit then is okay to ground the B-.
  2.   On receive, the transmit cathodes are opened ( S6 # 3 ) so the B- no longer is grounded, and the B- goes to ground via the receiver's bias resistor R25.
  3.  In the intermediate state, CALIBRATE  ( net ), the rec B+ is on, the transmitter oscillator is on, and the supply B- goes to ground thru 330 ohm resistor
             in the transmitter B- circuit. The oscillator plate current calculates to 26 mA, which thru the 330R resistor, posts the ~8 volts bias the receiver audio needs.

I'll have to look at that slightly hamified BC-474 and see how he's connected the power cable.
-H
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