trinityamps.com

Hi Matt,
The KT66's will definitely give you much more clean headroom than the 6V6s especially with the MV up, so long as the overdrive control is not engaged. Using the link input, I could put channel volumes up to 2 or 3 o'clock and still get a super clean sound. Of course, if you are using hotter pickups this might not be the case. I also found that just by rolling back the guitar volume a smidge to around 8.5 or 9 it really cleaned things up but still retained clarity.
With the KT66's the amp is LOUD! If you have the master volume up around 3 o'clock or more, you can have the channel volumes down around noon or so and still have plenty of volume and super clean.

I used a NOS Mullard 12AT7/ECC81 (CV4024) as the phase inverter tube. I tried a 12AX7 in that position and preferred the lower gain 12AT7. As for the numbers on the boxes, I would think it depends on the vendor. I did find this link on Doug's Tubes, which explains what his numbers mean: https://www.dougstubes.com/faq. I believe 12AT7's have about 60-70% of the gain of a 12AX7, but there are other differences between the two tubes as well.

Most of my playing was through a partscaster with low/medium output single coils (Lollar Blondes) as well as a LP with standard PAF-style humbuckers. Both were fairly clean at the settings I referred to above. Speaker cab was an open back 212 with an Avatar alnico A25 and a WGS Green Beret.

Preamp tubes were a mix of new production 12AX7s, and I used new production KT66's.

Here's a great link for comparing the various characteristics of 12AT7s: https://tubedepot.com/pages/tube-comparison-tool

I've not tried mine at high volume yet, but have pushed it through an attenuator (Palmer PDI) to get the master wound up a bit.

That showed two things. Firstly the master works well enough that there was no obvious benefit from using the attenuator, unlike my 18W TMB where it's essential. Secondly the Triwatt is very sensitive to pickup output, though perhaps running a Clapton Strat with midboost on shouldn't make that a surprise... But as stated above, it cleans up very well for dropping the guitar volume slightly, particularly with EMG actives where there's no loss in pickup clarity when you wind back the volume.

Generally, I would consider numbers like 115/115 and 100/105 written on the box to be some form of the sellers measurement of the gain. The 100/105 is either a high gain 12at7 or a fairly typical 12ax7. Some manufacturers will label a 12ax7 as a 12at7 if it’s mu is low compared to their standard. I think that’s what’s up with your 12at7.

As far as on edge breakup, I’d say your settings are pretty close to my experience with the Triwatt. I generally don’t use “live” speakers anymore, I run through a Captor 8 or 8ohm Captor X. I run the Triwatt with the master full out and adjust the Normal and Bright volumes to get low gain crunch. I usually set it up so that I get a good clean by turning the guitar volume down to around 6 and play lighter. Usually, that means I’ll have the bright and normal volumes somewhere around 2 o’clock.

It’s normal for a tube amp to sound different after it’s been running for a while. I find that the breakup sets in a bit earlier and sounds rounder after the amp has been running for a few hours, such as in a rehearsal. Also, if the amp is new(ish) it may still be breaking in. The tone will change somewhat during the break in period. It will also start to sound darker over a longer period of time (months/year) as the tubes and caps begin to wear out and drift. Preamp tubes don’t suffer this too much but, output tubes are affected more quickly by it. Especially if they are regularly pushed hard.

You also could try substituting a 12AU7 in the PI for super low volume. You wouldn’t get much output tube crunch, even running full out, but the amp would be much lower in output. You’d be able to drive the full preamp section, including the PI, much harder. It wouldn’t be particularly clean, but is good for grind at low volume.

A seller should not be labeling a "higher gain" 12AT7 as a 12AX7. While the gain factor is definitely a difference between the two different tubes, there is more to it than that. A 12AT7 is inherently/intrinsically different than a 12AX7.

Having said that, I really like the Triwatt with the 12AT7. Cleaner and more clear. Really suits the Kt66's. If you are using 6V6 for the power tubes, the 12AX7 as the PI may be a different story, but at that point it really becomes a different amp IMHO.

Actually, you said that backwards to what I said, as far as labelling. I didn’t say it was right, but it is what some of them do.

It is also a definite possibility that it’s a 12AT7 with a bit more jam than usual.

Sorry about that Jag....yeah I had that backwards but a reputable seller should not be labeling a 12A_7 as another 12A_7, no matter the gain characteristics. I agree that the issue may be a higher gain 12AT7.

Here's a pretty good thread on comparisons of different 12A_7 tubes plugged into a socket originally intended for a 12AX7.
https://el34world.com/Forum/index.php?topic=28043.0

Granted, the above table is not looking at the PI position but still might provide some good comparison data.

Since the OP mentioned that the master volume was no higher than 9 o'clock, I wonder if this is masking any effect the PI tube may have? The Pre-PI MV in the Triwatt is inserted between V2 and V3, so maybe the PI (V4) isn't being driven hard enough from the previous stages? Just a thought.

I suspect there may be something else at play here: I've tried a 12at7 and 12ax7 in the phase inverter position, and, at least at "family friendly" volumes (master at 9:00 or less) I didn't really notice much difference: with humbuckers and a hard strum, on the link input, I can get a little breakup with the two preamp volumes right around noon. For a 12at7, I used this JAN 12AT7WC, and for the 12ax7, I tried a Sovtek 12AX7LPS. When I buy 12ax7 and 12at7 tubes, I always get matched triodes. Usually there are two numbers written on the box. I noticed that the 12ax7 had "115/115" written on it, and the 12at7 had "105/100" written on it.

When I ordered the KT66s, I also ordered another 12AT7 (different vendor, slightly different tube I believe). This one had "80/80" written on it. I suspect those numbers represent the gain for each triode. If so, am I right in thinking my first 12at7 tube was fairly high gain, and likely closer to a 12ax7?
______________________
Alight Motion is the first professional motion design app for your smartphone for Mac, bringing you professional-quality animation, motion graphics, visual effects, video editing, video compositing, and more!

I agree with you. I am also using Alight Motion. It is one of the most powerful mods for creating animation videos. We can use its all templates for free.