[glyphmon]

To be clear, I wasn't thinking that the speaker wouldn't perform well.  I was more referencing the fact that it was doing the best it could with a single audio channel from an audio source likely not electrically ideal for the phono jack with a volume pot that needs cleaning.  I think the speaker did beautifully all things considered.  I believe it's in pretty good physical shape as well, having now removed it from the cabinet.  Before we get to voltages, see below:

   

Voltages all tested except one (expected values in parentheses, significant deviations in bold):

6A8:
  across heaters: 6.3V AC (6.3)
  pin 1: 0V (0)
  pin 3: 263V (264)
  pin 4: 61.6V (100) 38.4% low
  pin 5: -0.4V (-20*) ? - see note on asterisks
  pin 6: 172.3V (170)

6K7:
  across heaters: 6.3V AC (6.3)
  pin 1: 0V (0)
  pin 3: 263V (264)
  pin 4: 61.6V (100) 38.4% low
  pin 6: -3.97 (-3) 32.3% high

6H6:
  across heaters: 6.3V AC (6.3)
  pin 3: -4V (-3) 33.3% high
  pin 4: -3.16V (-3)
  pin 5: -0.798V (-0.3) 166 % high
  pin 8: 0V (0)

6F5:
  across heaters: 6.3V AC (6.3)
  pin 1: 0V (0)
  pin 3: 172.8V (170)
  pin 4: 102.4V (80V / 115V*)
  pin 8: 1.165V (1.2)

6F6:
  across heaters: 6.3V AC (6.4)
  pin 1: 0V (0)
  pin 3: 251V (264)
  pin 4: 266V (265)
  pin 5: -17.5V (-0.5 / -16V*)
  pin 6: -17.86V (-18)

5W4:
  both plates to ground: 325V AC (355)
  plate to plate: didn't test - anticipated 710V AC exceeds my meter's range
  pin 1: 0V (0)
  pin 8: 348V (340)

The asterisks are original to the diagram with the explanation that they represent the meter measurement while the non-asterisked number represents the value without voltmeter loading.

Observations about the significant deviations:
6A8 pin 4 and 6K7 pin 4 both share a connection to dogbone R4 (original, 22K spec, 21.3K measured in-circuit), and from there to electrolytic C16 (new), and from there to the oscillator coil.
6K7 pin 6 and 6H6 pin 3 likewise share a connection to R6 (original, 2.2M spec, 2.16M measured in-circuit), and from there to 2nd IF transformer
6H6 pin 5 is a bus connection to the 2nd IF transformer.

Thoughts?

Best wishes,
Roy