[paulbiagi]

Hello,
New to this forum, I've finished the BFlex except for one wire, which I'm not sure about. (I speak English and French, but can translate using the browser. Feel free to respond in German.)
The schematic shows a bias connection "CT H" between R24 and R25.
The bias wire appears to come from R103 to R25, however the layout diagram indicates a black line as "CT H". By convention, the black line would go to ground.
But if this point were grounded, R24 and R25 would receive 0 bias voltage, power tubes would red plate, etc.
What is the meaning of "CT H" on the layout diagram?
In pictures on two different builds there is a thick black wire connected at this point, but it's not clear where it's going.
Thanks for your clarification.

[paulbiagi]

I just figured it out.
It's the Center Tap for Heaters (CT H).
The CT for Heaters is not attached to ground, but floats DC at the bias level. Cool design.
(I had connected the CT H to ground like usual, without reflecting on the schematic.)
I'll make this change before testing.

[paulbiagi]

After reflecting some more, the bias voltage is negative.
Floating the heaters with negative DC could exceed the heater-to-cathode voltage rating of a preamp tube.
It seems floating with positive DC would be more desirable.
But if there's no hum, a float may not be necessary.
Am I missing something? Why would the heaters be floated with negative bias voltage?