Hi Gang. Whopadeedo. You stated "you preferr to run your gear with the tubes that were designed for it". Are you stating the spec for the rectification duty of your supratek is only rated for an gz34/ar4 and the 6106 doesn't meet spec? Your metal based gz34 is a fabulous rectifier to be sure[yes I have one] however, there are more than a dozen substitute rectifiers that will meet spec for rectification duty in your supratek.Please sir, don't interpret this post as being derogatory. Regarding regulation tubes....Mick recommends a max of 1.5 amps for heater current on the regulators. Well in the real world, that .1 amp draw for the heaters will fall well within the tolerance on any cuircuit designers paramaters if one is using regulator tubes to smooth the ripple of the rectifier, regardless of what type of rectification tube type used. The 6106 is rather unique in regard to run in time, as it requires a ton more burn in time than any other rectifier of it's type. The 6106 mated with the 350b's is any thing but lean in character regardless of the speaker used. I have auditioned your very own Merlin's in my own room and I would never ever consider it as sounding lean in character by any stretch, even in my rather large sound room [ 34ft x 27 ft x 12 ft ceiling] Great speakers by the way! I can remember responding to Bwhite's post as well as others regarding this very same issue in the original preamp of the century thread. If your 6106 was new out of the box, be rest assured; that 1 week of playing time isn't any where near enough run in time on the 6106. Furthermore... there is no better rectifier/regulator combo[6106/350] for any of the supratek preamps . Yes, the 6106 is closer in spec to a 5y3 than a gz34 however,it "isn't" a 5y3 and there isn't a 5y3 type rectifier on the planet that sounds anything at all like the 6106 in the supratek or any other gear for that matter. Your reply to Jazzdude regarding the 5y3 distorting sooner than a gz34 may indeed be correct. That said: a 5y3 type rectifier is NOT a 6106, and the 6106 will "not" distort sooner than my metal based gz34. It's the very same analogy as saying the metal based gz34 sounds better than a mullard, amperex, sylvania,phillips gz34. Patience my good man, give in more time[much more] you will surely be rewarded!