[glyphmon]

Having removed the screen grid of 6A8 from the circuit while preserving the connections between C15, R4, and the screen grid of the 6K7, there was 200V coming into R4 and 137V leaving it for the screen grid of the 6K7, so substantially similar to the result as with the tube removed (203V and 138V).  So, I would say this suggests that the screen grid connection is the culprit.

Just for the H**l of it, after reconnecting the wires to the screen grid pin on the 6A8 socket, I swapped my 6A8GT from the Philco back in to confirm my prior results when testing two weeks ago and still got 173V before R4 and 64V after, to the screen grids respectively, so the two tubes perform similarly.

So again, still confusing to me, if it is in fact a faulty tube that I should wind up with two of them that present in the same way, but this is not a possibility that I'm ruling out.  Is there anything external to the tube itself that could cause this unusual current draw, or is it pretty much confined to the internals of the tube itself at this point?

Shall I just order up a spare 6A8 and 6K7 to be safe?

Is the result being the same with or without C15 being connected helpful?  What are the implications of that test?

Best wishes,
Roy