Supro S6424 6973 (V5) no heater operation. Tube heats if swapped to V4

Hi. My keyboard player brought me an old Supro S6424(?) That has no output. I have built a few amps, ( kits, and scratch) so I told him I would take a look at it for him. 
First, I did a visual inspection. Removed the back cover and found a point to point wired amp, which is a new experience for me. Everything I have done is built in a turret or eyelet board. 
I rifled around in my Tube amp book, and also searched on the internet, and found a wiring diagram.  Not sure it is THE wiring diagram, because of a couple things:
1. The amp I am dealing with is old, not sure how old, but the output transformer is mounted on the speaker frame.  For me that dates it back to the 1950's or earlier, but again, I can't find any information or any definitive markings on the amp to know to sure what year it is. As it is vintage, and my buddies, not my own amp, I am proceeding with the utmost caution, as to not butcher an old amplifier...I guess I would call it respect. 
2 The speaker is a Magnavox, and labeled 1500 ohms. I measured its resistance, and it is 1478 ohms, which is pretty close, so I am not certain about the schematic, because it shows an 8 ohm speaker. 
At this point, I checked the tube compliment, and it is the same. 3 12AX7 preamp tubes, 2 6973 power tubes, and a 5E3 Rectifier.  I checked some of the B+ resistors, and again, they agree with the S6424 diagrams I have found. The cathode bias resistor is also the same at 250 ohms. I tested these resistors, and found there values to be well within specifications.
At this point, I decided to plug the amp in and verify  the complaint. 
Since I am being cautious, I decided it would be prudent to use my current limiter, built from a light bulb wired in series to an electrical outlet. 
I plugged the amp into the current limiter, and turned it on. The light bulb glowed dimly, indicating nothing shorted to ground. So far so good. At this point I again decided to carefully inspect the amp with it on. No sound output, which was my buddies original complaint. Upon inspection, I found the second power tube (V5) has no heater operation. All (5) of the other tubes have normal heater filament operation. At this point I figured "Oh this amp is old as dirt, probably has a bad tube. But rather than order new tubes I thought, " The other one is lit up, I will swap them." I did, and still no heater in the V5 position. So at this point, I'm thinking, yeah it probably needs tubes, but that's not what is wrong. So I decided to try to find more information. 
So again looking on the internet, I found this site, and I am hoping someone can steer me the right direction.
The puzzling thing to me is the 4 tubes after this one are lit, I have cleaned and tightened the tube sockets all with no positive result. As I said, the strangest thing is the power transformer filament goes to the indicator bulb, to V5, the last power tube that has no heater operation, then on to the other power tube and the 3 12AX7's that all have working heaters!
So here I am, very puzzled, and wondering what the heck?  Also, I know this amp has, at some time in the past, worked!
There are several other inconsistencies with this amp, but I am reluctant to jump in and try to fix anything until I am sure of exactly what I have here. 
I want to fix this amp, but I don't want to harm the vintage aspect of the amp. (My buddy didn't want me to put a grounded plug on it, so I don't want to change the amp in any way. Get it working, and sounding as it did. 
Any information, help, advise is genuinely appreciated. Thanks for being here, and if I can provide more details let me know.
John