It's not easy.

Assembling amps is easy, until you overlook one thing or another diagnosing them is time consuming and often requires dedicated equipment like a oscilloscope.

BUT, 5 will get you 10, this is a side-effect of you not knowing what you are doing while assembling this amp.  That isn't meant as an insult, but I'm guessing you don't know what heater filament wiring is usually omitted in layout drawings, and Nik doesn't supply schematics that show how the power supply breaks down and what voltages everything should read, making it harder.  Nik isn't in the hobby kit business, like Weber and a few others Ceriatone kits assume the builder knows their way around an amp.

Nik shows the filament connects to pins 2 and 7 of the power tube closest to the power amp (V5 on a 50 watt OTS, V7 on a 100 watt), but it is assumed that you will continue wiring across to the filaments to every tube, this is the power that a tube needs to operate.

So, you should have...

1.) ...wires running from the 3.15 taps on the power transformer to a terminal strip, and then have wires that take that current to the pilot light and to pins 2 and 7 of V5. 

2.) Well those wires need to keep on going.  Pin 2 of V5 is wired to pin 2 of V4, and pin 7 of V5 is wired to pin 7 of V4.  So that the tubes are both connect to the 3.15 taps in parallel.

3.  From there we feed the PI and preamp tubes.  Pin 2 of V4 is wired to Pin 4 of each 12AX7.  And pin 7 of V4 is wired to Pin 9 of each 12AX7. 

Then you should be supplying the heater voltage needed to power the tubes.

Some examples....
 
In this one, the orange wire is connect to Pin 2 of each power tube and Pin 4 of each 12AX7; the yellow wire is connected to Pin 7 of each power tube and Pin of each 12AX7.


In this one, the Green wire connects Pin 2 in the power amp, Pin 4 for the 12AX7's, the Black wire supplies Pin 7 of the power tubes and Pin 9 of the 12AX7's.


Nik has plenty of chassis shots on his site, but they a pretty poor on the details of the tube sockets, in some pics though you'll see Black/White filament wires, and on others you'll see Red/Black wires.  See the filament wires neatly tucked away on the edge of the chassis...

Oh, and I'll note, you'll notice that the 6.3 wires are all twisted, including those to the pilot light, this is to reduce hum.