Thanks, Marty. I look forward to your next post. The 100s are a top contender in my speaker upgrade (currently Vandy 1Cs.). FYI, I use a tube pre with a ss amp.
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Interesting results and I realize that your experiment was from the OHM's point of view. I have been experimenting with various tube types, but from the Prima Luna's point of view. I have owned the Prima Luna PL2 and PL5 for 3 years and have spent the better part of the last year experimenting on the PL5 with different tube types. What prompted this experimenting was the upgrading of my speakers from Acoustic Research 302 (3 way, 10 inch woofer, acoustic suspension) to Opera Platea floorstanders (2 way, 6 inch woofer, front ported). The other PL5 associated equipment is a Musical Fidelity CD PRE 24 (ss preamp/cd player) and a SONY SCD 555ES SACD player.
The output tube types tried were KT 88 (Svetlana Winged C), 6550 (Svetlana Winged C), EL 34 (Electro Harmonix), and KT 90 (Electro Harmonix). The speakers were tried only from the 4 ohm tap. Each tube type was used for at least 2 months.
I found the KT 90's fairly sterile sounding and not very engaging. All types of music sounded pretty lifeless. I wasn't expecting this result.
I felt that the music was the most dynamic sounding with the KT88's, only slightly less so with the 6550's. There was more than sufficient detail, but the music was not particularly sweet sounding. What was strange, was that both tube types didn't seem to last very long ... a few hundred hours at most. There was no particular pattern to it, the tubes would just seem to get excessively scratchy and noisy.
The EH EL 34's have become the keepers. The sound is dynamic, lively, and sweet. All ends of the spectrum are reproduced with good detail. The tubes seem to be lasting the longest.
Anxious to see your next post. I plan to try this experimenting with the PL2 next.
Since the thread is back, I'll provide a part II (or at least a part 1 of Part II):
I recently re-jiggered my system to allow me to fire up my ARC VT-130SE amp. This unit is balanced operation only. It has no phase splitter so I couldn't use it with my Joule pre-amp. My ARC LS-25 is back from service, so the ARC chain is now on line. The rest of the current system:
Sources are Cary 303 cdp
QSonix server with Benchmark DAC-1 or Cambridge DAC Magic
Oracle V/Graham/Nightingale or Acoustic Solid/Rega/Lyra Dorian via Aethetix Rhea
High pass is active at 80hz via NHT X2
Low pass/Room Analysis/PEq is at 74hz (for Ohms, 80hz for Maggie SMG) via Velodyne SMS-1
2 X SPLR 8 subwoofers
The ARC produces app 125 WPC via 4 X 6550 output tubes. Rich pretty much nails my take on 6550s. Like KT88s, the upside is dynamics and the downside a little less tubey sweetness. This is true of the ARC, which sounds pretty neutral - not obviously a tube amp from the tonality. However, this amp has a certain body to the mids and imaging that shows that its heart is indeed made of glass.
Unlike the Prima Lunas loaded with KT88s, the ARC doesn't sound slightly "hard" through the mids, merely less "sweet" than P/Ls with EL-34s. In short, it's a mid way point that's (tonally) awfully close to the P/L with KT66s that I had previously settled on. I'd be pretty hard pressed to describe much in the way of difference in sound, except that:
The ARC significantly improves the dynamic performance of the system. It's only 3db of headroom vs the P/Ls, but this is a case where the result sounds like more than that. The LS-25 also allows higher gain than the Joule so it's possible that some of this result is attributable to the switchover in pre-amps. Either way, the dynamic improvement is welcome and separates this amplification chain from the previous choice - for this application.
As a side note, there was much less tonal shift with tap changes on the ARC than on the P/Ls. Don't have a clue why, but I'm not sure that I could tell which taps are active on the ARC by ear. Subwoofer matching was pretty straightforward - although some of that may be my improved experience at this task. The NHT X-over got the A/D/A conversion out of the main signal path. I think it sounds better and I know it provides improved peace of mind.
In sum, the ARC chain will be the primary choice for my bi-amped speakers. (The improvement in dynamics is also obvious when I roll in my SMGs to replace the Ohm 100s.) I'll probably switch the TAD SS amps and/or P/L monos along with the Joule Pre back in at some point to refresh my reference point, but as of now, the high powered ARC tube amp seems like the best choice for my Ohm 100s.
Good question. My room has bass issues so I haven't tried (non EQd subless) full range operation. I could shlep the whole system downstairs (like I did when the Ohms first arrived) and try full range operation in my living room. OTOH, I'm probably too lazy. So, a guess will have to do.
The subs relieve the main amps of a lot of their work. It's plainly beneficial with the subs doing their thing, so I suspect that it's as (or more) beneficial stand alone. The question of how much juice you need will also turn on your listening habits and your room, but I think, a good general statement for Ohms is:
"More power is better, tubed or SS."