Not a silly question in the least.  I only have experience with Nik's 18 TMB and 18TMBEF86 but have built a number of other 18's based around other transformers.  For a thorough study I would spend a few hours sifting through the 18watt.com old posts.   Each circuit variation has it's own thing going on and all sound glorious. 
But, very simply...
The standard 18 watt has a normal and trem channel.  The 18 TMB has a TMB tone stack in place of the trem channel.  The 18ef86 has the TMB instead of trem and an ef86 with a 6 way tone selector as the "normal" channel. 

Well, unless Nik had a typo in his email to me.......yup. 

Hey Chuck,

Great review.  It seems we are all having a nice honeymoon with this amp.  There is one thing I've been trying to slightly "dial out" though.  On the OD with the PAB on for the typical RF tones I'm wanting to soften a wee bit of harshness in the upper mids and then the amp will be perfect.  I've been plugging all my NOS ax7 stash (amperex, Mullards, telefunken, Syls, Matsushitas) in V2 and the early 60's Sylvanias are absolutely the smoothest in this amp but there is still a hair of adjusting to do.

Thus...

 I've been spending a lot of time over at the amp garage site and have found this fine tweaking of the upper OD harmonics is where the magic occurs.  And the problem is, each amp is different and the guys over there who have been obsessing over these circuits for YEARS have developed the magic touch that gets the last 10th of a percent, that last piece of the puzzle of "the tone" equation figured out.  I think that is what you are paying for when you buy a Glasswerks, Bludotone, Carol Anns, Fuchs.........you buy "in the tone zone" expertise.   
That is never what I wanted or particularly expected from the Overtone.  I wanted exactly what Nik provided; an extremely well made ODS amp that gets me to the 99.9% stage.  Hell, this Overtone hangs with ANY of the "big boys" I have ever played,,no question.  The last .1% is personal taste anyway so this is where my OCD...lol......gets to do it's thing.  Now, it's down to component adjustments, pickups, guitar body woods, brands of strings,  seasonal humidity, moon phase and gravitational pull on electrons in my Winged C's.......lol,   yep.....OCD.

Oh,,,so close...

I'm "vibrating" with anticipation, hint hint....lol

I'll buy one......if the price is right......

Good to see you got the amp.  Get that thing biased right, crank it and let us know what you think of the OD.  The clean channel speaks for itself, eh? Best and most varied cleans I've heard in a long time.

I've been searching hi and lo for a 65 to no avail.   I'm fairly happy with the Emi. RW&B but by all accounts the G12-65 is THE speaker for these amps.

What pre's you were using?  I assume you were NOT biasing at 3ma.

EF86 is Vo,, then V1......  Be careful,  the phase inverter is V2 in this layout where it is more commonly V3 in most other designs including the Trinity SIII 18 wattTMB.

The old original Fender units were made to run straight into a clean amp.

Yes, he did a great job.  In a previous lifetime...lol....I was a videographer and I know that even a simple  video with a little compositing and green screening takes some time.  Ah...If only I had some time...

Thiagozt,

Can you post some pics of the problem area?  Maybe we can see something you might have missed.

I've always wanted a stand-alone reverb unit.  I just never got around to building one.  I think a reverb kit would fit in nicely with Nik's tweed offerings.

I agree with the BYOC kits...I've built the fuzz, script phaser, and the screamer clone.  Great kits, great tones and reasonable prices.

I've been planning to but I haven't been able to get any time to get in to my buddies studio.  Bedroom recording sounds good but it does the amp no justice not fired up.  I'm off to Hawaii for a couple weeks so after that for sure....ok?