Best modern 6550 tube for ARC per-amp

good input ralph

the ref 6 is a true balanced model though... but probably what you say still applies...

question -- would a 6550 that sounds good in an audio amplification role be necessarily a ’good sounding’ one when asked to do voltage regulation, or are certain other characteristics of the tube more important when acting as a regulator?

@tubegb

So, now one of your proposed strategies is to place a tube of questionable history, possibly fake, and with untold/undetermined hours of use in your $15,000 preamp?

lol...

well i guess we have all scratched the scab off of a healing booboo, make a bloody mess ... sometimes in spite of what is good for us... path to nirvana is often over some rough terrain in parts

just a note to the op - who is seeking info here

don’t mind us tired old hacks here on this board doing a little keyboard jousting in the late night... some joust better than others when scotch or burgundy or ........ is involved  :)

what you will hopefully take away substantively from here is that given the ref 6 uses the 6550 in the ps voltage regulator function (and not a primary signal amplification function) replacing that tube for hopes of better SQ is a ’maybe’ proposition - certainly more of a 'maybe' than upgrading the tubes actually handling the music signal (even though that can’t be done on your unit given the 4x 6h30p’s...)

but yes, in practicality, it all matters (more or less is the main issue at hand) and it is just one tube, so it’s hard to waste too much money chasing a ’maybe’ in this case - i would still suggest checking in with greg at arc to get his take/advice - they made the amp, their input is valuable

my post below was only sarcastically referring to your ref 6 as a p-o-s -- hopefully you don’t take that seriously, we all know it is a lovely piece, one of the very best - i have the ref 3, love it, can only imagine how sweet the ref 6 sounds

cheers and good luck

well there you have it, op - the experts and truly knowledgeable have spoken... yes, everything matters... of course it does!... no concern over matters of degree, or relative importance, sensitivity of inputs on the ultimate output/objective function ...

your $15,000 p-o-s minnesota made linestage has a sucky, marginal PS circuit that requires a gold-plated, absolutely best sounding tube (when used in a totally different application) to sound its best!!! yes -- be sure to get your money’s worth now... remember, we can’t take it with we when we expire, right?

now excuse me, need to join my fellow parrots as we listen to some birdland  :)

op

you do realize that the audio research ref 6 linestage uses its single 6550 tube as a voltage regulator in the power supply section, feeding the 4x 6h30p controlled gain section, right? this has been the case since the ref 2a model... where the power supply/regulation circuit incorporated a single 6550

as such, you do not/will not ’hear’ the 6550 in that unit as it does not directly participate in the amplification circuit of the audio signal... unlike 99% of other amps using that tube as the power tube pushing/pulling the actual musical signal...

given this, i suggest you simply follow arc’s factory guidance on what 6550 tube to use... longevity and adherence to performance spec as designed is more important than any perceived sound quality difference  -- or email greg christensen at arc service/support and ask him what they recommend as an upgraded 6550 for your ref 6 (they may say there is none)