Sir Brian. . . . . .

On that set of your's, there is basically just the full B+ buss and the sub B+ buss.

If you will consult the attached marked up schema, one sees the RED MARKUP B+ moving to the right from its derivation at the rctifier toobie. Then upwards, to feed that full supply level to the AF output tube supply.

Further tracking of that buss, transversuing to the left, has a minor tap off to further drop the B+ to the early stage AF tube. Next stop to the left is a full supply B+ level to the target anode of the eye tube.

To the left from that last area is the feed to the plate of your 6K7 if amp tube along with a further path to the left to the plate of the hexode portion of the 6K8.

Now, in going back to the sub B+ buss, it is derived from a voltage divider bridge of R14-R17 [YELLOW]that ties into the main B+ buss.

The sub B+ power flow is to the left via the FUSCIA MARKUP it branches apart to feed the screen grids of the 6K7 and the 6K8 on one run.

The other run feeds over to the left and then up to the plate of the oscillator section of the 6K8.

The sub B+ level would be dependent upon the main B+ level, the ratio of the R14-17 divider resistors or the current consumption of the tubes tied in to it.

Seems like a slight fault with the sub B+ level as it now stands, are R14 and R17 to spec ?

On the other aspect, of the 300VDC level on the main B+ buss , a wee bit high, but I do consult with the RCA Radiotron Tube and Design manual and see the 6K8 being used up to the mid to high 200V levels.

Matter of fact, in its compared performance with 100 VDC on the plate of the hexode , the conversion efficiency amd overall performance is appreciably better when using the higher voltage.

An aside thought, since I am uncertain about WHICH post, recently, and WHO it is / was . . . in which case was the mentioning of the use of a 1 K value power resistor in place of a field coil on a radio.

Should this happen to be the set involved, the reason for the higher derived B+ voltage just might be due to the
use of a 1K value of power series dropping / filter resistor. The value should be 1,500 ohms instead.

73's de Edd