I'm working on a Howard 256 :
http://www.nostalgiaair.org/PagesByModel/224/M0009224.pdf

The transformer CT does no go direct to chassis but it is above it by a 300 ohm multi-tap resistor.
The schematic shows the voltages at the 3 tap points as 3v, 4v, and 13.5v and the schematic note says these points are measured from ground (chassis?) as a reference.
The thing is I measure these all as negative values with respect to the chassis.
Is that correct? And if so why does the schematic show them as positive values?
If you can't read that schematic clearly use the model 225 which is basically the same circuit but the picture is larger and clearer:
http://www.nostalgiaair.org/PagesByModel/220/M0009220.pdf

Is this basically the same as later models that always use a 150 - 300 ohm resistor from the output tube's cathode to ground? ..to raise the cathode 13v more positive?

This is the same general method of biasing. The tapped resistor allows different bias points for various grids. Using one resistor which feeds the entire radio doesn't necessarily save space because the resistor is usually large, but it can afford better filtering, as this resistor will act as a resistive choke, much like the resistors found in the B+ circuit of AC-DC radios, and those choke-less/field coil-less AC radios. Thus the resistor can act as an additional filter and a bias supplier all at the same time.

Regarding the voltages, it is odd that they didn't put a minus sign at the voltages. However, you can always assume that with this conventional circuit, the center tap is going to be more negative than the chassis. Current only flows one way through a rectifier. It flows from cathode to anode. Therefore the plates are more positive than the cathode, the cathode is more positive than the chassis, and the chassis is more positive than the center tap. I'd go into more detail regarding actual electron flow verses conseptual thought on the subject, but this would only confuse matters. By reading the above you can get the basic idea as to which direction the electrons are actually flowing.

Thomas

Thanks Thomas.. it helps to get another confirming view.
But while I have your attention, Sir.. could you give me your 2 cents on the cap value differences between the two drawings?
It looks from dates on the prints that the model 225 was Dec 1937 and the model 256 was Feb 1937.
If that's true then can we suppose that changes to certain caps were made as an improvement over the earlier model?... and if so while I'm recapping should I follow the model 225 since it's dated later?
Speciffically I'm in reference to c13,c14,c18,and c-16?
I see so many variations in other radios too of the value of the coupling cap to the output tube... many use .01 but also there are so many .02s and .05s too... which way makes the best improvement in audio?