I have not started dinking round with the tubes in my OTS yet. But I have a lot of experience with the tubes in my super reverb. The biggest variable* factors affecting its tone, and point of break up are the pre-amp tubes (mainly V2 since that is the channel most used) and the PI tube. A balanced 12AX7 in the PI is mandatory. I use JJ ECC83S from Eurotubes. He sells exactly what  he advertises. He tests and categorizes all his 12AX7s. You buy the tube "balanced", the balancing is a virtue of the manufacturing process. Not something that you do to the tube. The 12AX** tube has two halves. On the PI tube each side feeds the output tubes 180 degrees out of phase. It is not important to know what that means, but in knowing that much you can see why you would want the 2 outputs of the tube to be matched or "balanced". I have found this to be very important, especially at higher volumes.

* I am assuming that you will not be changing speakers or other soldered components on a frequent basis. The pre-amp and PI tubes seem to have much more affect on tone than the Output Tubes.

When I replaced the transformers in my super reverb, I had it set up for EL34s. I learned that the circuit has a lot more to do with the tone than the output tube. Ialso found out that I liked 6L6s a little better, but we better start a new thread if we get going about tube choices.

As ususal, people seem to have definite but varied experiences that are at odds.

 Here's mine: I am player, not a hobbyist, but  I believe in doing basic maintenance on my gear. I read the articles on biasing and adjusted my amps accordingly. 42mA is right at the range of a "hotter'" bias, but within the "70%" recommended. I think you could get up to 45mA or so depending on your plate voltage which is the other part of the equation.

Now the counter: I have a great amp tech who does all the serious work on my amps. He insists that a lower bias is better and it does not effect the tone (I know, I know, the argument will start now). He says the tubes will last longer. I have done the bias comparison on my Bassman and Super Reverb and I have to admit, that he seems to be right. Since both these amps run 6L6 tubes and plate voltages 450-470 which is similar to the Overtone I think the same settings will work. My amp tech sets them up at 25-30 mA (brrrr cold). They sound great to me.

Matched tubes (+- 5mA, preferably less) seem to be much more important than bias, especially at higher volume.

Try lower the bias and let us know what you think

This is mot directed a jzucker, but just a reminder to all of us on this thread...
1. There are many factors that affect tone and how a speaker sounds and without being able to compare under identical conditions a definitive comparison cannot be made.
2. You cannot really tell how something sounds form a recording. As good as Marin's and others samples sound, we are not hearing the real thing. You can only get an idea of what the real thing sounds like. I purchased the OT based on Marin's and Sami's sound samples, but I was truly blown away when I got to play through the real thing and I have played through he best out there.
3. Tone is relative, one person may like a darker sound. One speaker may sound really good for certain things and not for others. I was able to AB my G12-65s (Rola) and they just did not sound as good as the V30/G12-30H combo. They weren't bad, just not as good. Moreover, I would bet that no one would hear the difference on a Youtube video.
4. A good player using the Overtone with any speaker with compatible ratings/specs will sound good. A specific speaker choice is to put that special touch on your tone.

All that said, if any one has had a good or bad experience with a speaker I appreciate their input. Thanks!

I am going to second Jzucker & SPM. The G12-65 is darker than the Vintage 30. I have a 2x12 amp with Rola G12-65s and a cab with a V30 and G12H30. I felt the V30/G12H combination covered the tonal range of the Overtone Special much better. Humbuckers sound pretty much the same with either set of speakers and settings for the Robben Ford tone on the Overtone. You can really exploit the versatility of a Stratocaster with the V30/G12H combination driven by the Overtone Special.

Enjoyed your acoustic clip very much. Now I know what that FET input is for!

It certainly does. It is kind of scary. I used to have a kind of reverence for my Super Reverb & Bassman. Since I've had the the Overtone Special I am seriously thinking of selling my other amps. Not for the money, but for the simplicity and elegance of it. I am convincing my self to wait till the honeymoon is over...then I'll realize that I really do need those other amps for something, right?

P.S. I was in hurry to get out the door when I was typing my last post. Sorry about those typos!

I have a 66 Super Reverb. Over the years it has slowly, but surely, been almost totally refurbed with top drawer components. It has Kendrick Blackface speakers and a few Kendrick mods as well. It is an exceptional sounding amp, at this point it would be hard to find a better sounding AB763 based amp. That said the Overtone Special sound just as good on the Clean channel and gets very good distortion at lower volumes. I cannot get the tone I want in the Super Reverb at volumes that other people will put up with. I get pretty nice sustin and break-up with a Les Paul (and 12AX7 pre-amp, PI tubes) at about 4. I have to crank it 6-8 to get a good tone with a Strat. You can use a tube screamer or something to brig that volume down a bit. But it will get too buzzy al low volume. The OTS sound about the same even at low volume. I I had to have just the one , the OTS would be it.

Greetings to all on this thread. I just wanted to say that I had some anxiety about this whole passive effects loop issue on the Overtone. Now that finally have the amp, and have had a chance to check things out, I am  not sure what the fuss is. First, (this just my narrow opinion) I am not sure why somebody who was into using a lot of effects (or likes the POD XT) would want an Overtone Special. What makes it "special" is that it sounds so very good all on its own. It is hard for me to fathom why anyone would want to modulate that in some way. I do understand the use of a little delay and/or reverb. I run a Line 6 Verbzilla and a Visual Sound H20 Chorus Delay through the loop and they sound just fine. Neither of these are very sophisticated or top-rated.

That said, if you have found some way to improve the overall performance of the Overtone Special by using some kind of ***alator or other device I would be interested to hear about your experiences.

I only have a few hours in on my new Overtone Special but I have used that time to see what kind of tone you can get with some different speakers. I have a 2x12 Avatar (open back) Cabinet with a Vintage 30 and a G12H30 and I have a 2X12 combo amp with two vintage  Rola Celestion G12-65s. After AB'ing them, the Avatar Cab sounds much better. Putting all 4 in parallel at 4 ohms does not seem to improve the overall sound much, if at all.  I am using very articulate cables (George L 1.55 guitar to amp, Mogami speaker connection) for the Avatar cab, and a less articulate cable to the Rolas so the jury is not totally out yet.  What can say is that the Avatar/V30/G12H combo sounds very, very good (It also sounds very good with my THD Bivalve).  This combo has a nice tight bottom end,  a very smooth transition to break up and very articulate highs, good harmonics, and no harshness at any volume. At this point I would not hype the G12-65 as THE speaker. My guess is there are a lot of speaker and /or speaker combinations that make sense for this amp. It is also my guess that this amp will make almost any speaker (with an adequate rating) sound good. It is just a matter of how good you want to sound!