12AX7A and AT7 tubes


I recently changed all 8 power tubes (KT88) in my 8 year old Mac 2102 power amp. Used Gold Lion tubes as recommended by the majority of the Audiogon respondents to I thread I ran asking for KT88 advice. As suggested, these tubes really made a difference in the sound produced by the 2102. I am now thinking that maybe I should be replacing the 4-12AX7A and the 4-12AT7 tubes as well. I am pretty sure there is nothing mechanically wrong with the OEM tubes currently in the amp. but I am just interested in what this change would do for the sound, if anything. I have some questions about this move. First, do you think this is a worthwhile investment? Second, if this is a good move, what tubes do you recommend? Lastly, should I also change out these tubes in my C2200 preamp? If cost gets to be a factor, would you do the preamp first, last, or not at all? (As an aside, Upscale Audio recommends the Mullard CV4004 and CV4024. The CV4004 tubes are a whopping $80.00 each. Are they worth it?)
frepec
Oops, that's Mullard 8162, which is a mil-spec tube, as I believe is the 6201...
Addendum...I'm hearing GREAT feedback regarding the New Sensor (?) reproductions of NOS Tung-Sols, Mullards, etc. Worth checking into since you need more than 2-4 tubes...
I posted regarding "best tube choices for Jolida Music Envoy preamp" a little while ago. Great comments above, guys...yes, the Mullards are generally warmer, and the Teles, Siemens, etc., a bit more detailed and analytical. I LOVE the combo of Bugle Boy AX7s (Great detail, imaging, AND a good bit of harmonic richness) with Mullard AT7s. The Mullard 6182 is a good step up from the 4024s, and the 6201s are ALMOST on a par with the Miniwatts / Bugle Boys / Popes...very, very close. Just a tad less 3-D, but about as perfect a tonal balance as you will find in a 12AT7 IMO...
I posted regarding regarding "best tube choices for Jolida Music Envoy preamp" a little while ago. Great comments above, guys...yes, the Mullards are generally warmer, and the Teles, Siemens, etc., a bit more detailed and analytical. I LOVE the combo of Bugle Boy AX7s (Great detail, imaging, AND a good bit of harmonic richness) with Mullard AT7s. The Mullard 6182 is a good step up from the 4024s, and the 6201s are ALMOST on a par with the Miniwatts / Bugle Boys / Popes...very, very close. Just a tad less 3-D, but about as perfect a tonal balance as you will find in a 12AT7 IMO...
As a routine in service rounds it was common to change out the the 12AX7A's at a rate of 2 to 1, time wise, vs the 12AT7. The AT7 is just that much more rugged a tube.

I don't know if the 7025 is made any more. It is the low-noise/hi-mu version of the AX7. If we could get out hands on these, they always got put in the signal path.
No small signal tube, that is currently manufactured(outside of EAT Cool Valves) can provide the sound stage/timbre/overall music reproduction of a strong, quality(ie: Mullard/Brimar/Amperex/Telefunken/Siemens)NOS valve(pre 70's). If you enjoy the warm, sweet, British flavor- The Mullards that Kevin recommended will provide that nicely. You can't beat him in the customer service game either. If you go with anything other than NOS; you'll be missing much that's contained in your recordings. Don't rob your ears! Finish the amp first and, should you feel the sound "just right"; you may want to try some Amperex in the pre. For less warmth/more detail; Siemens or Teles, Mullards/Brimars for another big warmth injection. Are the Mullards worth the money? You might consider that they are an easy 10,000hr tube, and that you'll probably fall in love with their sound and presentation. Careful though- Quality NOS tubes are highly addictive to the music lover.
The 5751 is often used as a substitute for the 12AX7 although the gain factor is somewhat less (70% of the 12AX7). Depending on the circuit, this may not be noticeable.
How about considering using 5751's instead of 12AX7's? Apparently most of them are better. I think some of the best could be Sylvania Black plates..For more info on this, check out Joe's Tube Lore; he provides a very detailed account of his listening experiences with 5751's, 12AU7's and 6922's.
Also, just by the way, regarding Chinese Shuguang tubes, I have purchased a quad of Shuguang EL34's for my C-J MV55 amp, amd found them to be immensely superior to the Electro-Harmonix of the same type I had in there. With EH 6CA7's, however, it's a completely different story.
Just a final update to close this out. I did change out all the 12AX7s and all the 12AT7s in my amp and preamp. Used NOS Mullard CV4024s (12AT7) and Mullard re-issue 12AX7s. (Couldn't afford the NOS Mullard CV4004s). Anyway, bought all this from Kevin at Upscale Audio. He really knows his tube stuff and the company is great to deal with. Fair pricing, also. This tube upgrade was really worth the time and expense! Thanks to all who responded.
Frepec might as well replace the cheap fuses with audio grade fuses like HiFi or Isoclean.
Frepec finish the MC2102 and then later move to the C2200. In the MC2102 you have to replace 4 input and 4 driver tubes compared to 2 phono and 2 high level tubes for C2200.
Actuallly the price of a used pair of Blackburn Mullards, not re-issue, maybe a worthwhile experiment albeit expensive if the tubes are from a seller who will stand behind the product. The best current production is the Tung Sol either gold pin which many think is better than the steel pin. I like the steel pins just fine. However a warm expansive good condition real Mullard they are not. The Sinos have a bit of tipped up treble emphasis so you might not like it. Tpsonic I got mine for the same amountas you 2+ years back on epray and trelja gave me a pair or two. They don't burn in much do they! Doug is "out of stock" which is really a bad term he can't them anymore than the others. The reason is they were taken out of production.
Thanks for the responses. Some of you are asking about what kind of sound I like. I want precise sound, not flabby. I do not want thin highs that lead to listener fatigue. I like full sound stage sound that blooms. I do not want overpowering bass but do want bass that is full and rich. The Gold Lion KT88's really expanded the soundstage and gave the music more "presence." I would like to continue to build on that. I have read some reviews of the re-issued Mullard that say it is almost as good as the NOS version. Do you agree? Also, still interested in should I finish the 2102 before I go on to the C2200 preamp or do the preamp first?
I believe Dougs' tubes has them (8+9G).At least they did as of earlier this year.I sent two friends for them.I bought 8 matched off E-bay some years ago for about $5/ea.
Tpsonic,
After telling you of these remarkablebtubes. Mind you not the absolute unamynous all time weorld best but a decent really cheap tube from the Sino conglomerate Shuguang, I can't souce them. So I ask where did you find them? To the original poster no other shu is worth your time it really must be their 12AX7C or 9th edition only. no more than $10 a tube. Mike Sanders of Quicksilver audio insisted that a new owner of the Triodes stick with the because he thought they great and voiced those amps using them. Our buddy Trelja was as skeptical as i a was which dictated extirpating the offensive terrible excuse for a real tube never mind a good one. It took quite a bit of convincing so just to make him stop harrsing me I said OK and paid 9 bucks for a pair of brand new 9th ed Sino branded Shuguang. And I would not be writing this novel if I wasn't floored by them. Shu has made more with the B or 8th for the biggest group of tube consumers the shreding electric guitar guys . It just didn't distort readily therefore useless for guitar and good for audio. Now they are gone.
Depends if your direction is wanting to extend highs and smoother midrange with very low noise floor. The 12AX7s will effect your sound the most compared to the KT88s.

I would change the tubes in the preamp after you complete the MC2102. I put more money in my preamp tubes than the my MC275 amps. If I had to do it over I would have increase my money into my MC275 tubes using long plates with big warm sound and lower noise.
I think it is most important to know which direction in sound you want to go with the new tubes...Many good tubes you could use but,would be nice to know if you want a warmer 12ax7/12at7 or a neutral sounding tube...Whole lot of difference between a Mullard and a Telefunken....Amperex Bugle Boys are somewhere in the middle....
Try the Shuguang triple mica 12ax7s (G9).These were discontinued,but still available.About $10-11/ea.