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Power tubes as drivers -- Line Magnetic

I just purchased a LM 518 IA, which is a 22 watt SET integrated using 845 tubes. The amp uses 2 6L6 as drivers and 12ax7 for input.

I'm picking up the amp this week, and although I haven't seen the user manual yet, From what I can gather, virtually any power tetrode or pentode, including EL-34, KT-88, 6L6 and 6V6 can be used as a driver in this amp. Of course that means I'm getting ready to try a buncha tubes.

My current thought is to pick up decent, but not expensive, current production samples of the various tubes (probably all made by the same manufacturer to maintain some control) so I can get a handle on which sound I prefer most, then move on to more expensive and probably NOS versions of those tubes I like best. Just checking in with the community for reality check on if this makes sense to anyone else.

Also, I've seen on various tube sellers sites reference to "this (noisy/micro phonic) tube is only suitable for use in a driver stage . . . ." Can I infer from this that I can get away with slightly dodgy driver tubes and thus buy really fancy schmancy tubes in low grade and still achieve good results?

Will appreciate your thoughts.

D
dkidknow
atmasphere's avatar
atmasphere
11,753 posts
 
We operate our amps in A2 mode as well. Fisher in the 1950s that made the first A2 amplifiers that I ever heard of.
dkidknow OP
59 posts
 
Ralph-- you might find it interesting that my Merlin TSMs, which are 8 ohm nominal and 6.5 minimum, are really enjoying being driven off the 16 ohm taps of the Line Magnetic. I'm getting a very open and extended sound but all of the bass definition I could want.
charles1dad's avatar
charles1dad
10,249 posts
 
Dkidknow,
Congratulations with the new amplifier. I get the impression that the Line
Magnetic 845 amplifiers are exceptionally good and possess excellent drive
capabilities. Based on owner reports like yours and also reviews, these LM
SETs are using high quality output transformers coupled with good power
supply design. As Ralph noted, the driver tube/ stage is robust.
I don't think Ralph would be surprised with your results using the 16 ohm
tap, you have to experiment with different speakers to find the best tap
usage. This amp offers much flexibility to tailor your sound with driver tube
choices. Also different brands of 845 offer additional fine tuning, there's
great potential with your amplifier. I believe that it's a true High End bargain.
Charles,
atmasphere's avatar
atmasphere
11,753 posts
 
Dkidknow, yes, the Merlins are an easy to drive speaker. I think that is the most popular speaker used with our M-60 amplifiers.
dkidknow OP
59 posts
 
Thanks for the input Charles. The amp is still breaking in, but I'm confident I'll get to a good place. My dealer was nice enough to let me bring my speakers over to audition them before I bought, and the combination was very engaging. I'm going to let the amp and tubes really settle in and get a handle on the sound before rolling tubes. I do have some mid 1990s Svetlana 6L6s around the house as spares for my guitar amp, so I suppose I can pop those in to see how they sound.

As far as Merlins being easy to drive, they certainly do have that reputation, and I know Atmasphere amps are generally thought of as a very good match for them. However, as I mentioned above, I first paired the Merlins with the Leben CS-300, and the Leben really couldn't drive them in a satisfying manner. This was strange, because the Leben did an amazing job driving a pair of Dynaudio Focus 260s, which at 4 ohms nominal impedance, would theoretically be a harder speaker to drive.

I also think the Line Magnetic is tonally just a better match for my Merlins-- the Leben sounded a bit lean on the Merlins, but fantastic on the Dynaudios. By the same token, the LM/Dynaudio combination yielded some plummy/wooly bass, but through the Merlins produced the best bass I've ever heard from my speakers. It would have been interesting to hear the more powerful Leben CS-600 paired with the Merlins, but that amp was just a bit too expensive.

Truth be told, I was pretty sold on Leben when I went to the store and was just trying to make sure they could drive my speakers. There was really no contest though and I had to change my plans.
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