Those are diodes, not resistors. They are being used as a fail safe for the rectifier tubes. You can read about it here:
http://www.premierguitar.com/articles/the-immortal-amplifier-mod-1
P.S. Sorry to reply so late but this board has been very slow so I don't stop by very often.

   Agree 100%. But the OP said:
Then Texass said:
   I just thought it best to point out to those of us who are not technically inclined that no power tubes are being shut down with the switch.

      I'm pretty sure you are referring to a Pentode to Triode switch. Not the same thing as a 1/2 power switch. A 1/2 power switch in an 18 watter would require going from push-pull to single ended output. That would be nuts.

tooloud, I was excited to read your post as I have a couple of AO-29 chassis in my basement and I was wondering if they could be used for this build. Were you able to use the output transformer from the AO-29 or did you have to get another? I'm a bit confused about the AO-29 as some models seem to output to a standard speaker while others use field coil speakers. I'm not sure what I have or if it will work. Any pointers you can offer would be greatly appreciated!

    The name on the left is the British designation, the name on the right is the American. An ECC83 is a 12AX7 and an EZ81 is a 6CA4. Same tube, different name, depending on country of origin. Many tubes are marked with both.

Paul Ruby amps has a great start up article here: http://paulrubyamps.com/info.html

Cool! (I love a happy ending)

     Yes! Yes there is:
http://www.premierguitar.com/Magazine/Issue/2007/Apr/The_Super_Secret_Transformer_Tester.aspx
    Article by the venerable RG Keen.

You wouldn't happen to be running a Sovtek 5Y3 for the rectifier would you?
My understanding is that the Sovtek is not a "real" 5Y3 and will produce some funky voltages.

I went down that road here: http://ceriatoneforum.com/index.php?topic=1780.0
Personally,  I feel it's a mistake to not offer the Fender reverb circuits but what the heck do I know? 

Yes! Check out Alwalt's thread:
http://ceriatoneforum.com/index.php?topic=1444.0

   The "New Fashion" :
http://www.sozoamplification.com/index.html

This sounds plausible.

More complex than the Overtones? Really? You may be correct, Nik stated just a little while ago that he completed a layout for a Vox AC30 but then shelved the idea as being too complicated.

I certainly understand not offering reverb on Marshall, Dumble, etc. but to offer a line of Fender amp kits without a single reverb circuit? Fender is the industry standard for reverb! This is a glaring omission and not an unconscious decision.
      Bottom line is that a Princeton Reverb is very high on my list for a future build and I still can't get it from my favorite amp kit supplier, Nik!

Why Nik/Ceriatone is avoiding offering anything with reverb?
I'm curious but I don't want to waste Niks time with an Email.

You need a multiple of two power tubes operating in a push-pull amp.(2, 4, 6, etc.) Because a 36 watt amp has four tubes, half (two) can be shut down for half power. So no, you cannot do this with an 18 watt amp. You could do the Triode/Pentode mode switch thing but it's not really the same. I've heard good things about Mr. Hall's VVR mod, that's probably your best bet.