I really have no idea, but....
Where did you get the drawing from?  Is it a working creation, or just theory?  It seems pretty straight forward.  I guess the idea is to lower the B+ to the preamp so you do not burn up the tube in the cathode follower position.  I guess a 12ax7 can take about 200 volts in the cathode compared to just 100 for the 6N-2P.
Don't mean to waste your time, this is kind of over my head, but why make the change?  Is there some advantage with the octal pre tubes, have you heard this circuit before?
Seems like there should be more info.  For example, what value components do you use to bias the 6N-2P?  What about the rest of the circuit for that matter; like grid/plate resistors and coupling caps?  Do you stick with the same tube all the way through the PI ?
You may already know all of this stuff.  I sure would be interested to know what all of this adds up to.
Thank You and Good Luck

Hey seeker -
How is it possible you know how to read plate current, but not voltage?
Which makes me wonder, are you measuring plate current from the cathode that is grounded via a 1 ohm resistor?
Anyway... to measure plate voltage, set your meter to VDC, clip on to chassis ground, put your probe on pin #3 and see what you get.  This will give you the other half of the power equation.  
Plate voltage or plate current by themselves is somewhat "useless".  It is important to know both numbers.  So let's see what you get......

I think "lightice" may be leaning in the right direction.  But I am pretty confused at this point, probably my own fault.  So if you don't mind me going back over some common ground......

1.  I am not familiar with these amps at all, so pardon me for asking.  This amp uses 4xKT66 in the output and is SS rectified, is that right?

2.   Are you saying that you see 550VDC on your plates, and your current is between 34-40 MA?

3.  I am not sure if the KT66 is a 25 or 30 watt tube, but at 34MA your power is almost 19 and at 40MA your power is up at 22.  Even if the 66 is a 30 watt tube, your 70% mark would be 21 watts, obviously at 25 watts that mark moves down to 17.5 watts.  So I am thinking that maybe you are pushing the limits of what would be an advisable bias.  But it all hinges on what numbers you are seeing at the plates.

Can you confirm you plate voltage one more time?

Have you checked your bias lately?  A mismatch in the output tubes can cause this problem.  Not a mismatch of 4 or 5 MA, but something a little more extreme.  Does not matter how new your tubes are, they can take a shit on you at anytime.  By the way, have you tried a different set of tubes?
Again, I would not hesitate to contact Nik. He seems to have a genuine concern/interest in his customers.  I am sure this problem can be fixed.  Especially considering how pleased you seem to be with this amp; it really needs to get corrected.
Good Luck

seeker -
Nice review.
If the ghosting continues, you may want to try/get Nik's opinion on increasing the B+ filtering.
Good Luck

I am not the sharpest guy in the world, so pardon some questions.  Are you building a new SL from Ceriatone, or is this a vintage Marshall?  If you have a Ceriatone, did you look at their layout?  It shows pretty clear on the layout where to wire the trim pot.  Although, on the layout, it may appear to you to be a 50k resistor; but it is actually an adjustable pot.  It kind of lies between two 10 mic e-caps.  One end and the wiper are tied to ground, while the other end is tied to a 47k resistor. 
I do not have a Ceriatone, but I have a 1971 metal panel.  Our trim pot is actually 25k, but everything else is the same.
Good Luck

I have always heard the name Marstran whenever guys talk about transformers, but I know nothing about them.  Were they pretty easy/helpful to deal with?

Hey -
DMM is a Digital Multi Meter (amps volts ohms etc.).  If you do not have one of those I would say you are at a disadvantage.  Probably best to do like you say and tech it back to your tech.  Just make sure you are as forthcoming as possible with the guy.  Give him as much info as you can about what is going on. Even if something seems unimportant to you, tell the tech anyway and let him decide what is valid and what is not.  Good luck, and definitely let us know the outcome.

I would say your biggest problem is that you associate with someone who would decide to record in a "hotel room", and then request that you find a way around "unwelcome volume.  You are in a band, and the biggest problem this guy foresaw to recording in a hotel room is the volume from a Fender Champ?
Other than that I would suggest buying a Shure SM57.  They have recorded huge numbers of guitar amps over the last few decades.  A good quality, used, 57, is very affordable.
Good Luck

Oh Man, is this still going on?  Have you tried new power tubes?  Do you have a DMM?  You must have a short somewhere.  I would suggest trying power tubes that you know are good,  or you can even try your tubes in another amp. 
Take your DMM, put it on the tone/buzz/bell/noise setting and start looking for a short to ground in the power supply and bias supply.  Where do you live?

I have heard of the Yellow Jackets of course.  So the Tube Bones are similar, interesting.  Just never paid much attention to that stuff.  Sounds like they work real good for you.
Thanks for the info.

How does this work???
Thank You

\\

Sounds like all you did was cut the parallel connection between the two out jacks.  That shouldn't be a problem unless something is shorting out somewhere. ( Pictures? )  Have you played your amp anywhere other than your house?  Can you take your amp to a friends house and try it there? 
Something is not right with this story.  If it does not blow fuses at your techs shop......  You either have line problems at your house, or there is a piece to this puzzle that we are being denied.

Like I said in my first post, we bought the "basic" Sozo's.  That is to say, the least expensive caps they make.  Not even sure if they had the "Vintage" caps then.  My gut feeling is that it is not worth the money to buy coupling caps that cost as much as the Sozo Vintage, or even more expensive.  Of course to back up my statement, I would have to do a similar test with the "Regular" vs. "Vintage" caps. 
I really believe that Mallory and Orange Drop caps are very good  and toneful enough for anybody.  There does seem to be a lot of builders who use Sozo in their amps.  (I believe Doug Roccaforte is one of them.  And I have nothing but respect and admiration for that guy).  Don't know if the builders use Sozo as a selling point or if they really hear a difference themselves.  I think the "Basic"  Sozo are 2-3 times the price of Mallory 150.  For most people I think they are probably worth a few extra dollars.  Who knows, it all kind of gives me a head ache after awhile.

I am pretty sure Hoffman sells Slow Blo 1/2 amp.  If your PT burned up it is  possible it took something else with it.  It very easily could have stressed a tube or filter cap.  That part may work for a while, but fail later.  Who replaced the Out Tranny?  They may be able to give you some guidance.