Try with power tubes removed.

   Those readings are all good.  Where is the 7th tab on the transformer?
The schematic shows that it is the one with the thermal fuse.  You need to measure resistance from the 7th tab to any of the other 6 on the primary.

The funny thing none of us have mentioned, this transformer can be wired up for any voltage, so it could have been rewired and you would not have needed the external transformer.

Edit:  I think the 7th tab is where the white is connected up on the secondary side (with the orange and black wires).

  The fact that you measure the same voltage on all taps of the primary is precisely the reason we suspect the primary is open.
  As others have suggested, you must check the resistance of the primary winding.

  I also see 19V marked on that transformer.  Aside from the secondaries I don't see what that could possibly refer to.
  Maybe whoever drew up the schematic with the (24VDC listed where it should show AC), specified that the transformer maker also mark it that way?

  I think that the one piece unit would turn out to be a major disappointment.

  The piece of wire connecting those 3 pins on the jack must be removed.  The way it is wired all jack contacts are grounded and it can not work.
  Also, the pot you replaced (3rd from jack), it looks like one of the legs is bent over and the solder may be touching the ground trace.  You need to make sure it is only touching the trace it connects to.

  Thrift shops can be very cheap sources of consumer electronic items to be used for parts.

Doc, is that the service manual from elektrotanya ?

 I don't think it will be like the Yamaha:

  Just to add a little to what Enzo said, to increase the power supply usually means installing a larger power transfomer, and some amount of re-design.
  So your point about needing a different amp to get (a significant amount of) more power is probably correct.

 :tu:

 Ok, that resistor assortment looks much better than I expected.  I was worried there might just be 500 individual resistors thrown in a bag for you to sort out.  Looks like they are separated by value, with more of the most common values.  Price is reasonable, the only thing to keep in mind is they are 1/4 watt, which is fine for any battery operated device, but may not be useable in some other powered circuits you may build in the future.

Most of those prices you paid are fairly reasonable, except for the very generic individual electronic components, like the caps, led, and battery snaps.
It's fine for a one off project, but if you do more building check an actual electronic supplier such as Mouser, Newark, Digi-key, etc.
  As Roly pointed out, simple items like some of those caps are inflated 10 to 100 times for price.

 Ilyaa:  You probably read about it, but I'll mention it for others who may read this thread, the bias circuit you posted with the resistor that connects to the HV AC,
(http://music-electronics-forum.com/attachments/547d1175892694-kscan_0001.gif) that circuit will only work if the PT is center-tapped.

  This is with or without the transformer?

  Just a few more comments to add to what others have mentioned.
Lower gauge number wire is thicker, so it will always be able to handle the current, but may be stiffer and more difficult to work with, in this case I think 22ga will work fine instead of 24.
  A 1K trimmer is not a switch, it is a trim pot.  Generally, trimpots are miniature versions of pots that are adjustable with a screwdriver rather than a knob.
  Pretty much any .1uF cap  will be rated at least for 16V, so any should work.
Big bags of assorted parts are not always a good value, some times there may be 3 useful ones and a hundred you will never use.  In this case, I don't know how many different values of resistors they have in that assortment.  If it's a lot, you will have a hard time sorting through all those color codes to find the ones you want.

And I agree with Roly, $80 seems quite high.  Could you do a breakdown of the more expensive items?  If some are ridiculous, perhaps you could take them back and get them elsewhere.  I had thought this would be quite a cheap project, if a lot of it is general supplies not specific to this unit, then that is more understandable.