12ax7 vs 5751

I have not read every post in this thread, so I will apologize ahead of time if I am repeating any previous comments.

I have Rogue M180 monoblocks that for a year or so I used with Silverline SR17.5 bookshelf speakers. I used the 5751 with them and it was great. I eventually acquired some Silverline Bolero floorstanding speakers and the 5751 didn't work well with them at all. The sound was just, well, blah. I replaced the 5751 with a Telefunken rib plate 12AX7 and the system was dramatically improved. With that substitution the tube compliment in my amps was Telefunken rib plate in the 12AX7 signal tube position, RCA 12AU7 tubes in the driver position. I have since replaced the RCAs with Telefunken rib plate 12AU7s.

I also have a pair of Telefunken smooth plate 12AX7s. I put them in the signal tube position and both me and a buddy noticed that the leading and trailing edges of transients were slightly smeared compared to the rib plate. I prefer Telefunken to all other tubes I have auditioned and/or used in my system (the others being RCA, Tung Sol, Amperex). But to me the smooth plate Telefunken is slightly warmer than the rib plate. Both are very, very clear, but I preferred the dynamics and crispness of the rib plate, and once they break in, mine were NOS, they are actually quite sweet. Smooth, clear, dynamic, fast.

Also, in my headphone amp I have a smooth plate 12AX7 and smooth plate EL84s, but I plan to replace the 12AX7 with a rib plate - it's on order and should be here soon. We'll see how that goes, in that application the smooth plate may be the ticket!

Anyway, back to the original question, I think the 5751 is a great tube, but I've been very happy since moving on to the Telefunkens.

Reynolds
When you say "the leading and trailing edges of transients were slightly smeared"...
Does that mean the high frequency is smoothed out? Sorry if the ? seems silly but I have Focals and they seem to be a bit on the bright side, just wondering if tube change has the potential to balance that out a bit. Of course much of the sound depends on the recording.

i did some rolling to and forth between the ei elites and the telefunkens today. there really isn`t much if anything between them. the telefunkens definately have a wider soundstage. the sound seems to go beyond the speakers which i really like but in pretty much all other area`s i couldn`t really tell the difference. the ei elites, one side is slightly microphonic but again it doesn`t really effect the sound performance at all.

i have my pioneer bluray player plumbed into the amplifier and watched shrek earlier. the sound was really good. music scores in the film sound excellent and voices throughout the film sound very natural. of course there`s no explosions or the like in this film so i can`t comment on stuff like that plus i have to think of the neighbours! music on this film certainly has some punch though!

by the way i`m from the uk and had our first snow fall today! i`m praying it stays for at least some of the week so i don`t have to go to work lol more listening time for me hopefully!

describe microphonic

Mcpherson,

No worries, it's certainly not a silly question. I'm not confident that I can answer your question about the brightness of your system to total certainty, but I can perhaps explain my earlier comments a little more clearly.

I want to make sure that my comment about the slight smearing is in the proper context. I was comparing Telefunken rib plate 12AX7 to Telefunken smooth plate 12AX7 in the signal tube position of my Rogue M180. The driver tubes were held constant with Telefunken rib plate 12AU7. The Telefunken were already my favorite tubes for detail, dynamics, speed, tone, and certainly clarity. The comparison between the smooth and rib plate is really getting down into the small details, I like either one better than anything else I've had in my system, and I could live happily with either of them and never look back.

We were listening to acoustic guitar with the rib plate 12AX7 first, then swapped it out for the smooth plate. After a few moments we realized that a little bit of information had been lost in the sound of the strings in the trailing edge of the notes. At the edges of these notes the rib plate was more convincing, the smooth plate just very slightly fuzzy. But as I mentioned before, I could live happily with the smooth plates.

I think the rib plates have a smooth sound, which to me means the sound isn't edgy. I just think rib plates provide a little more musical information around the edges of notes than the smooth. I was on another thread where the discussion included RCA tubes (which I used before moving to Telefunken) and one someone commented that Telefunkens were a little brighter sounding than RCA, so perhaps changing tubes could help you. I moved to Telefunken because I was hearing dynamics and clarity. I've never had to battle brightness in my system, and I made the change too long ago to remember that aspect of the RCA sound. But along those lines, RCA is warmer than Telefunken, and Mullard is warmer than RCA. If the other Audiogon member's comment is indeed correct, then maybe changing tubes could solve the problem of brightness in your system.

You didn't mention anything about the rest of your system other than the Focal speakers - do they have beryllium tweeters?

I asked the guys at the stereo shop today about your questions. Several comments were made, but there wasn't too much discussion, so I'll just relay the comments: (1) Focal are bright sounding speakers, (2) yes, it is possible to reduce brightness with a change in tubes, but they would need to know more about what is in your system, (3) would first be looking at your interconnects or speaker cables, (4) wondered if you had silver cabling in your system as that can sometimes add brightness.

As far as tube microphonics, if you google “tube microphonics” you'll get plenty of hits. But you don't want any microphonic tubes in your system. I had a very microphonic tube in my preamp once and just touching the volume knob was amplified through the speakers.