Just rolled my pre-tubes!

[Geoffcin]

The Ming Da amp came with a set of Sovtek 12AX7 (7025) tubes, but since I already rolled the driver tubes to Sylvania's I thought I would try a set of NOS Sylvania long plate 7025's.

Tubes are almost exactly the same gain, quite, and no microphonics that I can tell. I'm reserving my decision on the difference in sound quality until I can get a few hours on these tubes. So far so good!

[Hyfi]

The Ming Da amp came with a set of Sovtek 12AX7 (7025) tubes, but since I already rolled the driver tubes to Sylvania's I thought I would try a set of NOS Sylvania long plate 7025's.

Tubes are almost exactly the same gain, quite, and no microphonics that I can tell. I'm reserving my decision on the difference in sound quality until I can get a few hours on these tubes. So far so good!

The older sovteks are still real good. The newer ones are noisy.

Here is my dilemma. My pre uses 2 12au7s and 2 12ax7s.

Which ones would I want to roll first, and which ones have more effect on the sound?

To make things worse, 90% of the time I have been listening via Passive so neither of the tubes should be being used. Passive gives me much greater control over volume steps and low level listening. But, right now I am up in the office and the unit is set to Normal Gain and Yokeshire- Shape of a Dancer is rockin the house at a pretty good volume level.

Right now I am using older Sovtek 12ax7s and newer JJ Tesla 12au7s. I don't have the spare cash to go nuts but would love to have the oportunity to roll a few of my own

[Geoffcin]

I wish I could help you, but I'm not sure what kind of topology your amp is using. With mine it's really simple.

The amp has; two 12AX7's preamp tubes, two 6SN7GTB drivers, and four output 6550/KT88's, or KT90s set up in a push/pull configuration. The amp can also be switched from ultralinear to triode by a switch.

I didn't think about rolling tubes for almost a year, but when I got the Sylvania 6SN7's there was a noticeable gain in the bottom octave.

Now I've got two totally different designed 12AX7's so we'll see how it goes.

[poppachubby]

Sounds good Geoff. I would deifinitely like your opinions when you feel ready. My EICO HF85 is being overhauled and I think some rolling will be in order. I have the original Mullards in the entire unit. That's 5 - 12AX7 and a single 6X4 rectifier. One pair for the low gain, one pair for the high gain and a single 12AX7 in a final stage. Both signals channel through this before moving onto the rectifier. A most excellent design.

My Mullards test well and frankly, they sound great. I am most concerned about my low gain and would like to roll that pair, and perhaps the final stage 12AX7 as well.

I am quite positive I will try the TJ Full Music. I will buy them from Ian Grant.

Again report back on your findings. Perhaps I can send you a pair of the Mullards to try out once I have the TJ's in place. Geoff check out the TJ 6SN7's, they are reportedly a real sonic gem.

http://www.grantfidelity.com/site/ca...tj_full_music_

[Geoffcin]

I let the amp warm up for about two hours today playing FM while I was out of the room, so I am finally listening to the amp at it's full/best operation temp.

First the new tubes are dead quite just like the Sovtek 7025's they replaced. With the input shorted even at full volume you can only detect the slightest hint of some noise in the right channel with your ear pressed at the tweeter.

Two, I take it back about the gain being exactly the same. The Philips tubes seems to have slightly more gain than the Sovtek tubes.

I've played a few of my favorites including some test tone tracks, and I'm hearing some differences, but I hate to say the jury is still out. This "after work" reviewing really is not the same as a fresh set of critical ears Sunday morning.

More to come!

[JoeE SP9]

The older sovteks are still real good. The newer ones are noisy.

Here is my dilemma. My pre uses 2 12au7s and 2 12ax7s.

Which ones would I want to roll first, and which ones have more effect on the sound?

To make things worse, 90% of the time I have been listening via Passive so neither of the tubes should be being used. Passive gives me much greater control over volume steps and low level listening. But, right now I am up in the office and the unit is set to Normal Gain and Yokeshire- Shape of a Dancer is rockin the house at a pretty good volume level.

Right now I am using older Sovtek 12ax7s and newer JJ Tesla 12au7s. I don't have the spare cash to go nuts but would love to have the oportunity to roll a few of my own

Got a schematic? That would help a lot.

[poppachubby]

Yes Joe is right HyFi. Most likely one pair of those 12A's are for high gain and one for low. If you listen to CDs and AUX inputted devices like an Ipod, you would want to change out the high gain for sure. I don't hear you talk about vinyl much so assuming that's not your bag, just leave the least valuable pair in the low gain.

[Hyfi]

Yes Joe is right HyFi. Most likely one pair of those 12A's are for high gain and one for low. If you listen to CDs and AUX inputted devices like an Ipod, you would want to change out the high gain for sure. I don't hear you talk about vinyl much so assuming that's not your bag, just leave the least valuable pair in the low gain.

Not sure if I have a schematic or not. I'm still kicking myself for getting rid of all may albums the year I bought my first CDP.

I have swapped out the AX7s to find that the older Sovteks are much quieter and also that I got a bad batch of EHs from Parts Express. When I got the pre, the guy had 4 12ax7s in it which did work but not proper. After getting bad batches of stuff from PE, I got the JJs from Quest For Sound, and used a set of ax7s I had from my Sound Valves pre.

[Geoffcin]

OK,

Here we go again. After discounting the effects of break-in I'm going to have to eat my words.

First off I wanted to make sure that it wasn't me that was getting used to the new tubes, but an actual effect I was hearing. To that point I lent the system to my better half who proceeded to break it in with everything from Anita Baker to Luther Vandross. I wasn't in the room for most of it, but the sonorous effect was noticed throughout the house until a sudden stop. With a sheepish grin, (but somewhat ashen face) she came out and gave me the news that she had toasted the amp.

Of course I played it up; I immediately dashed into the room and grabbed the amp like it was my beloved pet and exclaimed "What have you done?!" as I held it's lifeless body in my hands. Of course I knew what had happened. Somewhere during Madonna's "Immaculate Collection" an output tube decided to meet it's maker. Not the first time I've smoked an output tube, but a first for her!

So now after installing a new output tube and checking the bias we now have a real chance to check out the amp. Of course I couldn't open the amp up without tweaking all the pots, but really they were very close so I don't think I've changed the sound much.

The new Sylvania 12AX7's initially sounded dull compared to the Sovtek's they replaced. Dull and cold was my first impression. They do not sound that way now. In fact if anything they are slightly warmer than the Sovtek. The real change from initial installation to now is the upper register has clearly opened up. There's a lot more "air" in the upper registers on par now with the Sovtek which had great extension.

What I would call the greatest difference between the two tubes is the Sylvania has brought up the "holographic" effect another magnitude. The amp always gave a spooky "right there in front of you!" effect with closely mic'ed vocals, but now it's like the music is coming from places I've never heard it before. The best description I could make is that the soundstage has jumped two feet off the speaker plane, and wraps itself nearly to sides of my seat. Honestly I was half expecting to hear sounds behind my head!

So, although my initial impression was one of disappointment, I can say unequivocally that these NOS Slyvania 12AX7's represent an upgrade over the Sovtek tubes they replace.

[Hyfi]

What were the letters on the sovtek after the 12ax7?

[Geoffcin]

What were the letters on the sovtek after the 12ax7?

12AX7WA

[Hyfi]

My older ones that sound better are WXT. The newer LPS tubes send all kinds of hash through my current VAC Pre but did not exhibit this with my older Sound Valves pre.