Looking at the receiver board schematic, if T401 is on the board, you should see DC continuity from pin 7 on IC402 to pins 7 and 9 on IC403.
The time to do a DC continuity check on a trifilar winding is BEFORE you put it on the board.? At that point, you can verify that you have three independent windings.
Pin 7 on IC402 goes to the "hot" side (dotted) of the first winding.? The cold side of the first winding is AC grounded through C406, and gets 1/2 Vcc bias through the R401/R402 voltage divider network.
The hot side of the second winding is connected to the cold side of the third winding.? This is what produces the balanced output to pins 7 and 9 of IC403.? This common point is connected to the AC ground/DC 1/2 Vcc bias network described above, meaning you will have continuity on the board from the hot side of the first winding to the common point of the second and third windings, and from hence to the far ends of the second and third windings, giving you continuity from pin 7 of IC402 to pins 7 and 9 of IC403.
In short, the continuity you are seeing on the board is perfectly normal.
NOW, the Power Supplies schematic shows Vcc to be 5.6V.? 1/2 Vcc is 2.8V, so standing current in the voltage divider resistors, ignoring bias current draw, is 280 uA.? That's not a lot.? Without looking at the datasheets for the ICs, to see what they might actually draw on the bias leads, my first reaction (left over from bipolar transistor land) is that this is probably not stiff enough.? I'd've put a buffer on Vcc.? I'd probably at least glance at using a TI "rail splitter" IC to develop the 1/2 Vcc bias voltage, and, again, I'd worry about available current.
I'd also worry about frequency response of that RC network.? The tradeoff is frequency response vs. charge/discharge time, which controls regulation of the bias voltage.
--John WB5YOO
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On Mon, 16 Oct 2023 21:12:59 -0700, "K3KDW via groups.io" <r.gammon@...> wrote:
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I have continuity between the left A, B, C, and pin 7 as noted in the instructions. The right A, B, and C, share some continuity with the left. Is this correct? I expected these would be independent.
--John R. Strohm WB5YOO
