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Can you put a 12AU7 in any 12AX7 circuit?

Mr. Lin

Mr. Lin

Lunatic Member
I have a Jolida 100 tube CD player that uses two 12AX7 tubes. Is it safe to try using 12AU7 tubes in it? I know the 12AU7 is lower gain, I don't know what any other differences between the tube types are. I have such a wonderful collection NOS 12AU7s I'd love to try with this CD player.

Thanks
 
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Mr. Lin said:
I have a Jolida 100 tube CD player that uses two 12AX7 tubes. Is it safe to try using 12AU7 tubes in it? I know the 12AU7 is lower gain, I don't know what any other differences between the tube types are. I have such a wonderful collection NOS 12AU7s I'd love to try with this CD player.

Thanks
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Not a good idea to use a 12AU7 where it calls for a 12AX7. You can sometimes get away with using a 12AT7 though.

There is a useful 12A_7 gain factor substitution chart here:

http://thetubestore.com/gainfactor.html

Cheers

Lar
 
Actually, you can use a 12AU7 without doing any damage or blowing up your equipment however, as you stated, it is a lower gain tube. I have tried a 12AU7 in place of a 12AX7 just to see how it sounds and it takes away half of the volume. If the circuit calls for or is designed for the 12AX7, don't use a 12AU7. You won't like it.

I like to use the 7025 in the place of a 12AX7.
 
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I know the 7025 is a drop-in for the 12AX7. Thanks for the advice, both of you, I'm not going to mess with it.
 
I don't know why one would want to do that unless they have a bag of 12AU7s laying around. There certainly are enough 12AX7s out there to satisfy most folks tube rolling joneses for a long time. That being said, I tend to favor triple mica black plate 5751s and realy haven't noticed any negative gain issues at all in my gear.
 
12AU7s aren't revered for sonics anyway. Pinwise they're the same and nothing will break if you sub them in.
Roll 5751s if you want neutrality and slightly lower gains. Which 5751 is best will depend on your circuit.
 
As others have said, a 5751 will do nicely with very little gain hit. I've had very good results using a number of quality 12AT7, 12AY7, or something similar. However, in my Fisher X101C, I get best results using only 12AX7 or 5751s because the circuit is in series and the 12AT7 family isn't able to complete it without distorting noticeably. I would never use a 12AU7 in a 12AX7 slot. The results are very poor indeed.
 
Andyman said:
I don't know why one would want to do that unless they have a bag of 12AU7s laying around. There certainly are enough 12AX7s out there to satisfy most folks tube rolling joneses for a long time. That being said, I tend to favor triple mica black plate 5751s and realy haven't noticed any negative gain issues at all in my gear.
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Like I said, I basically do have a "bag of 12AU7s laying around," that I used with my Wright 200C phono preamp. Some of them are actually quite good in that application. But I have an equal number of 12AX7s. It was just a thought really.

audiodon657 said:
12AU7s aren't revered for sonics anyway. Pinwise they're the same and nothing will break if you sub them in.
Roll 5751s if you want neutrality and slightly lower gains. Which 5751 is best will depend on your circuit.
Click to expand...

Funny thing though, I have some JAN GE 5751s that I've been using in the Jolida for the past few weeks. So far these are easily among the best I've tried in the CDP, however, neutral they are not. The sound was a little warmer, with emphasis on the midrange. In other words, more of a stereotypical tube sound, which is actually something the Jolida doesn't typically have with other tubes.

Of course ideally I'd like to try the Sylvania triple-mica black plates, but they're so damn expensive.
 
Hello, I really could use some help with the front 5 tubes in my Audio Innovation 800 MK3 power amp? There is 2x12au7 and 3x12ax7 and I dont know correct order!
No markings anywhere ??
 
When you substitute a different tube (like a 5751 for a 12AX7) in a phono stage from the one the engineers designed it around, then you are creating a FILTER. You may like the sound of that filter, but it does not conform to the RIAA equalization specification for the recording and playback of phonograph records, established by the Recording Industry Association of America and it is definitely NOT Hi-Fi.

Just to review: a tube's performance in a circuit is dependent upon the ancillary components (cathode resistor, plate resistor, etc.) and voltages (plate voltage, bias voltage, etc.) that ensure the device works in the most linear and lowest distortion part of the plate curves. Each tube type has a specific and unique mu, transconductance and plate resistance that require that the voltages that support that tube are correct. When you substitute tube type A for tube type B, you are simply creating a noise generator.

The Triode / Pentode Loadline Simulator is not only a fun device to play with but a very useful tool for the audio experimenter. Set up a tube type like a 12AX7 for lowest distortion, record the operating conditions and then set up a 12AU7 for lowest distortion and record the operating conditions. Now set up the 12AU7 for the operating conditions of a 12AX7 or vice versa. The results aren't something you would want to listen to.
 
Seems like there ought to be a manual for that Audio Innovations amp out there SOMEwhere... Anyway when you get the sockets sorted out, label them for the next poor schmuck!
 
I did it a long time ago with a Bottlehead Foreplay and I didn't blow anything up. But I didn't like the resulting sound.
 
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