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Rolled some 12ax7's recently...

Hi All,
I went through my supply of 12ax7's recently and found some goodies.
I recently compared Bugle Boys to Telefunkens in the phono stage of my pre-amp. Interesting (to me, at least). I found the Telefunkens to be nice sounding; very clean and clear, very nice detail, over all a very nice sounding tube. The Bugle Boys, however, were magical! WOW! Timbre was so much more apparent. The soundstage depth and width increased; especially the depth. The music seemed to come alive and glow. It was much more captivating.
I found such a dramatic difference between two high quality tubes very interesting.
I have yet to try 10m's, and 70's Mullards that I found. I will report when I do...
By the way, NOS Sylvania's sound nice in the line-level stage. All tubes reported are vintage NOS. I match them with my tube tester. And, I do not change the volume setting between tube brands tested.
Any comments are more than welcomed! I appreciate any information on your experiences with 12ax7's. The price of some of these NOS is incredible; I am glad to have these nice examples in my collection!
Cheers.
bicycle_man
nsgarch's avatar
nsgarch
2,524 posts
 
Bob, the RCA 5751 TMBP is my favorite 5751 (it's a REALLY tough call, but I still think I like it better than the Sylvania.)

I have mine in a Mac amp, but in a phono stage did you notice:
A. Any reduction in gain? Many are concerned about this, personally I don't think it would show up unless one is driving the tube over the brink!
B. Any (noticable) reduction in noise floor - you did say "clearer", so that might could be lower noise floor?
ptmconsulting
1,000 posts
 
I have a Hagerman Trumpet phono stage, and Jim Hagerman said not to use them over the 12AX7, but it sounds so much better. There was no reduction in gain that I noticed. In fact, it sounded louder because of the increased dynamics. It was also clearer but smoother on top. Could be a reduced noise floor. Don't know.

I do know that there was a very low level buzz in the Tung Sols that I was using before that is now gone with this 5751. Don't get me wrong, those Tung Sols are very, very good - a sweet sounding tube with clarity and kick.

I need to try the Tung Sol's in my preamp and see how they fare against the RCA Clear Tops I am using there now. Or perhaps try the 5751's in there and see if it betters everything all around or if they truly belong in the phono stage (I only have 1 pair, so a search for their best location is needed).

Bob
nsgarch's avatar
nsgarch
2,524 posts
 
Bob, "ruggedized" (for the military) 5751's (especially the triple mica ones) are supposed to be great in phono and microphone preamps because of their extremly low noise and/or microphonics compared to a regular 12AX7. Something I can't really judge as mine are in an amplifier. However, they are definitely smoother (by which I mean less in-your-face grainy) than the 12AX7's I've tried; and the really good 5751's are more dynamic too. -- Neil
.
galyons
1 posts
 
Bob,
Jim H, most likely doesn't recommend 5751's in the Trumpet because the RIAA is passive and the tubes contribute to the equalization. That being said. I am no RIAA equalization
Nazi and use 5751's, which I think sound great, in my phono pre amp. I am building a Cornet2 and will try them there, well.

Cheers,
Geary
ptmconsulting
1,000 posts
 
Update, I had some good ears over this past weekend and we played with a few different things. We did try swapping out the 5751's for the Tung Sols.

The impression was that the RCA Black Blate 5751's were a bit more dynamic but ultimately too plummy and slower on the bottom end. The Tung Sol 12AX7's were clearer and cleaner and faster all around. The general consensus was to leave the Tung Sols in.

Well, that's what this hobby is all about. Trying different things from time to time, but making sure to go back and see if a change is ultimately an improvement, or just a change.

Enjoy,
Bob
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