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Old 7th January 2007, 11:42 PM   #11
kevinkr is offline kevinkr  United States
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Hi Dave,
I couldn't agree more, but in some vintage applications and guitar amplifiers 12AT7 are commonly found. I wouldn't design any audio circuit with them except perhaps for a mi application or guitar amplifier..
"To argue with a person who has renounced the use of reason is like administering medicine to the dead." - Thomas Paine
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Old 7th January 2007, 11:46 PM   #12
SY is offline SY  United States
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My measurements correlate with that observation. I did a series of 1kHz distortion measurements with 1.7V bias and CCS plate load, 2mA. From the standpoint of distortion magnitude and harmonic distribution, far and away the worst tubes I tried were some branded Sylvania and some premium GE 6201. Far and away the best were JJ. Try those out at lower currents than people usually use and see what the fuss is about.
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Old 8th January 2007, 01:01 AM   #13
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I did a series of 1kHz distortion measurements with 1.7V bias and CCS plate load, 2mA. From the standpoint of distortion magnitude and harmonic distribution, far and away the worst tubes I tried were some branded Sylvania and some premium GE 6201.
Wow, a lot of people are dissing the 12AT7. I tested a bunch of different tubes for the driver tube in my SimpleSE. I needed a tube that could drive a 6L6, EL34, or KT88 to clipping from a CD player. I wanted a single stage, and preferably a triode, or triode wired pentode. A CCS load would be used if it offered an advantage. Of course I selected tubes based on low distortion, but I also wanted the predominant distortion to be 2H. I also wanted a tube that would be available world wide, and preferably still in production. It should not cost a lot either. When I designed the TubelabSE, 5842's were $5 USD each, now some can cost over $50 USD.

I found a few tubes that worked good, but selected the 12AT7 because they are everywhere, and still in production. I have about a zillion 12AT7's of several flavors. I listened to several different types, and made a list. Then I took the amp to an audition session where a few people listened to it. We tried some 12AT7's and they liked one of my top choices...... The GE 6201.

Why the big differences of opinion. I think it has to do with the fact that I feed them a lot more current than most people do. I found that these tubes sound best at 10 to 12 mA, with a CCS load. I find that many triodes sound best with much higher current than the usually accepted value. The limiting factor is often the plate dissipation rating. The 12AT7 can dissipate 2.5 watts and the 6201 can handle 2.75 watts (per section).

The 12AT7 will not replace the 5842, and I don't think that I would use a 12AT7 to drive a 45 or other high end DHT. In that use the amp costs enough to justify the expense of a 5842. However for a lower cost amp using a 6L6, EL34 or KT88, the 12AT7 (at 12 mA) works quite good. Since a few million were made, they should never get super expensive.
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Old 8th January 2007, 07:57 AM   #14
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Originally posted by kevinkr
IMO most US made 12AT7 sound lousy. European made ones were often very much better.
Ohhhh, but the US ones make such good geetarrr head fodder
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