2. amps-preamps
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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
rgurney
279 posts
 
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.
rodman99999
6,130 posts
 
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.
wenty3208
1 posts
 
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.
dbdeeb
15 posts
 
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...
dbdeeb
15 posts
 
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...
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