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derrickdj1

The 12AT7 swap for the 12AX7-Impression

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Today I substituted the JJ 12AT7 in the preamp for the Tung-sol 12AX7 preamp tubes in V1,V4.  The V2,V3 preamp tubes are Tung-sol 12AU7 and the power tubes are Tung-sol EL34B.  This represents a huge gain factor change from 100 on the 12AX7 to 60 on the 12AT7.  I had concerns would this make the power transformer work hard, push the power tubes more or less hard.  How did the substitution work?

 

After a couple of albums for sampling, the initial impression of the 12AT7 is that it is an excellent swap tube.  This tube is very delicate and smooth.  It brings out a bit more instrument and mid-range detail.   With pop music, there is less strident or grainy sound and smoothing of the overall performance.  Guitar reverb also sounds more pleasant.  I'm not much of a Rock fan and my first preference is jazz.  

 

The 12AT7 is not a popular tube in Hi Fi home use.  In guitar amps, it is commonly use as a phase inverter.  I did not know quiet what to expect tone wise from this tube and was pleasantly surprised.  I had read and see discussed that the most bang comes from swapping preamp tube. I have a variety of preamp tubes, next I would like the get some KT77 power tubes to substitute for my EL34B and 6CA7's.

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Derrick, you really should try swapping in good quality 5751's for the 12AX7 (although not in any phono section).  They are 30% less gain than the 12AX7, and are (typically) quieter and less microphonic.  I have them installed in lots of spots in my systems.  They are not cheap, but IMHO well worth it......

 

I do have a bunch of 12AT7's if anyone is interested.

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I have seen that tube, 5751 in a few threads.  People seem to really like them.  I may have to give it a try.  The lower gain tubes seem to cleanup some of the unwanted dirt in the preamp section of the amps from my reading.  I thought I would loose some low end with the lower gain tube but, so far no difference.  Maybe I can't tell since I am only using a few watts and would need some really spirited levels to hear a difference.  But, then I would have to leave the room due to the loudness, lol.

 

 

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2 hours ago, derrickdj1 said:

 I have a variety of preamp tubes, next I would like the get some KT77 power tubes to substitute for my EL34B and 6CA7's.

I have tried some Gold Lion K77, EL34B and 6CA7's in one of my SE amps and I prefer the 6CA7 sound. It will depend on how your amp is biased and your preference of sound ultimately. My favorite running in two of my SE EL34 amps. 

 

https://www.ebay.com/itm/NOS-Ip-Matched-Pair-Soviet-USSR-Era-6L6GC-6P3S-Vacuum-Tubes-Russia-Ships-USA/122208484248?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m2749.l2649

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4 minutes ago, wdecho said:

I have tried some Gold Lion K77, EL34B and 6CA7's in one of my SE amps and I prefer the 6CA7 sound. It will depend on how your amp is biased and your preference of sound ultimately. My favorite running in two of my SE EL34 amps. 

 

I do like the sound of the 6CA7 in my amp.  Just a nice thick lower end.  I am liking the thick lower end of the 12AT7 also, lol.  The Gold LionKT77's are not overly expensive.  I still find myself in ear training to pickup the differences with these tube changes.  I guess you can't get away from learning new things in this hobby.

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3 hours ago, derrickdj1 said:

Today I substituted the JJ 12AT7 in the preamp for the Tung-sol 12AX7 preamp tubes in V1,V4.  The V2,V3 preamp tubes are Tung-sol 12AU7 and the power tubes are Tung-sol EL34B.  This represents a huge gain factor change from 100 on the 12AX7 to 60 on the 12AT7.  I had concerns would this make the power transformer work hard, push the power tubes more or less hard.  How did the substitution work?

 

Glad you like it!

 

Couple things to think about.  The current difference is negligible, far greater current differences from switching the power tubes, for example.  the gain factors of 60 and 100 are theoretical numbers based on a minimum load, these are not the differences found in the real world, in practice they are far closer together, and the 12AX7 is doubtful to even hit 60 in an actual circuit.    A 12AX7 in a 12AU7 slot with typical 12AU7 plate and cathode resistances will barely make any more gain than the 12AU7, if at all, since it's not operating in it's normal conditions.  

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Depending on location in the circuit, the higher 2nd harmonic output of the 12AU7 could possibly be audible although probably subtle.  But, you can have fun playing with all of the 12A_7 series of tubes and their equivalents.  Of course, if you don't precisely level match at your listening position it will not be possible to make a sound (pun intended) judgment.  There's also the issue of expectation bias (another intended pun!) based on reading that a certain tube has specific characteristics (and that will depend on the piece of equipment in which the tube is used).

 

Maynard

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3 hours ago, tube fanatic said:

Depending on location in the circuit, the higher 2nd harmonic output of the 12AU7 could possibly be audible although probably subtle.  But, you can have fun playing with all of the 12A_7 series of tubes and their equivalents.  Of course, if you don't precisely level match at your listening position it will not be possible to make a sound (pun intended) judgment.  There's also the issue of expectation bias (another intended pun!) based on reading that a certain tube has specific characteristics (and that will depend on the piece of equipment in which the tube is used).

 

Maynard

I did not have expectation bias, I was more concerned about not causing any amp problems.  The 12UA7 in V2,V3 most likly will stay.  I have not read about people substituting these tubes due to the very low gain.  You know I start post in the tube section to pick the brains of some of our more experience tube affectionados.;)

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I understand your point Derrick!

 

As far as expectation bias goes, I encounter that all the time when guys I know buy some really expensive tubes because they read that the "Tung-Sol gray plate type XXX with D getter and manufactured on January 3, 1952" sounds better than any other tube of its type in existence.  Somehow that, in combination with paying $300 for the tube, does indeed make it better.  No one has been willing to take me up on my offer to try their preference with a blind listening test in which they don't know what they are listening to.  

 

Maybe Dave can do a little post about this from a psychological point of view.  It seems that when it comes to audio equipment, the prettier it is the better it sounds.  And, certainly, the more expensive it is the better...

 

 

Maynard

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Klipsch forum has already taught me that more money spent is not always better.  My tubes are new production and cost about $20 a piece for the power tubes and you already know, JJ tubes are bargain.  I am not a cable, power cord or other super expensive things.  Good setup, room Tx, good gear and quality source are my focus.  This will give the greatest gains.

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If anyone here is interested in a pair of NEC 12AD7 tubes pm and Ill send them to you. No charge. I see them listed as a "low noise low microphonic 12AX7" But I dont know anything about them! I pulled them out of an old sony reel to reel. I am not a huge tube roller so if you want to experiment let me know!

 

 

Josh

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Thanks for the offer.  I may take you up on it.  

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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:)

4 hours ago, derrickdj1 said:

Sure, I will take them.  PM sent earlier today.  Thanks!

:)

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Forum member @joshnich sent me a couple of 12AD7 tubes to roll in my amp.  I took out the two 12AT7's and popped them in.  I was very surprised at how authoritative the tubes were in the amp.  Very nice bass and detailed midrange and hi's.  The 12AD7's are twin triode rated at 450mV vs a regular 12AX7 tube at 300mv.

 

The amp took about 30 seconds longer than usual to make sound and get to the previous set volume.  I wonder is this is due to a re-biasing with the 12AD7?  Nothing else to note on the tube substitute.  They are excellent tubes after listening for a couple of day.  Thanks Josh!

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