Great..! Nik makes really good amps & his service is top-notch. I`ve never played a TW amp, but i can say the OTS i have a stunning.  Just keep in mind speaker choice seems to be critical to get the best from the Dumble style amps. There are a few posts here that cover the subject.. Seems to be the G1265 or EV for top choices for the D clones. I`m running a Mesa C90 black-shadow and it sounds great. I`ve also tried a JBL that had nice cleans, but sounded a bit too treble orientated & clinical with the OD engaged. Cheers

Yes.. if the method of selecting half power is triode, then half power can be used on a 50 watt amp that uses two 6l6 or EL 34 tubes.

Hey Toppscore, I use one of these with a vintage Hiwatt, works like a charm! My line voltages are between 120 and 123volts and the apc gets me down to 108 to 110volts, The Hiwatt doesn't want to see anything higher then 115volts max. Hiwatts have a weak bias winding. http://www.apc.com/resource/include/techspec_index.cfm?base_sku=le1200

Yep.. works on 100 watt amps. Go onto the ceriatone amp site and email Nik. He`s great to deal with and will confirm the options for you on the different amp models Ceriatone offers.
I presume the triode half power option could be applied to most amps he makes.. but he will confirm for you.
The half power option on my 100 watt OTS cost about $15 USD. Money well spent..!
Cheers... 

My OTS sounds great in both pentode & triode.
I think Niks half power switch to triode is an excellent mod.. giving the user more than one sonic option.
The amp still has plenty of balls and clarity in triode.. but it`s smoother, which can be a good option.
You can still rock out in triode, but if i were to play a jazz type gig, triode would be my choice.
There`s no mud at all.. just smoother and less in your face type tones.
IMHO the above makes the amp even more versatile..!
Cheers... 

Triode switching will work in a 50-watt amp, it turns off part of each power tube, but still uses all the tubes.
Myself, I'm not a fan of triode/pentode switching (some people are, your mileage may vary). Triode mode completely changes the dynamics of the power amp and makes everything "squishy" and undefined. The attack on the note becomes softer, the overdrive becomes less defined and duller, etc.  In can turn a high-gain amp to sonic mud.

It is a good insight that the typical ODS/OTS style amp, like many "hi gain" "cascading tube" designs is built around a big, clean power amp designed to deliver the preamp's tone without smoothing it over and muddying it up with power tube distortion. The exception is the Bluesmaster, which attempts to get some of the less-focused, less-defined, thicker Marshall tone going on. Amps like the OTS, Mesa Mk. series, Soldano, 5150, etc. can all sound great a low volumes because the power amp is mostly there for amplification, and has a lesser affcet on tone.

wyatt is right. Stop chasing low power in a high power amp. It aint there.

If you want a low power amp get one designed and voiced to do the job. I have tried Powerscaling, attenuators, pentode/triode switching, pulling output tubes, and everything has an effect and always not good. Attenuators down to around 6dB are OK, powerscaling in moderation is OK, lower sensitivity speakers (but you'll not get the speaker you 'prefer' in a lower power version, so another compromise), etc etc.

But actually, the OTS is already well suited to lower output volumes because of the way its designed, the output section is designed to run clean all the way up. You just need to voice it slightly differently for lower colume and possibly a few other mods to increase the touch sensitiyity in the pre-amp.

When Nik built my OTS 100 May 2012, i asked for the half power mod, which is a toggle switch on the rear panel.
In half power mode all four 6L6s are still in operation, but switched to triode mode from pentode.
This gives the usual reduction in expected volume & clean headroom from  100 to 50 watts, but the tone is a little different.
Four 6L6 in triode gives a smooth & warmer tone than two 6l6 running at 50 watts.
It`s not quite as punchy as 100 watt pentode mode.. but i prefer the triode 50 watt choice to both 100 & 50 watt pentode.
Actually.. i think these D clones run around 90 watts, so half power probably around 45 watts.
Anyhow, i can recommend triode mode as it gives the obvious volume reduction, but also a nice change in tone character.
Hope that make sense for ya..! 

Honestly, power supply, transformers, and speakers are all decisions that make a 10-watt and a great 10-watt amp and the same for a 100-watt amp...and they aren't the same. Ultimately, when one attempts a swiss-army amp, they have to start making compromising. Whether tube swaps, attenuators, power-scaling, master volume, etc., you'll always have side-effects trying to get bedroom- and stadium-level volumes from one amp.