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I've been trying to learn all of the replacements for the 12ax7.
From what I could find, this is the best list.
12BZ7*, 12AX7WA, 12DF7, 12DT7, 7025, 7025A, 12AD7*, 12AX7A, 12AU7A•, 7729, 12DM7*, 5751*, 5751WA*, 6057, 6681, 7494, 12AU7•, 12AY7, 12AT7, 12AV7.
* means parallel filament
• means may not work in all circuits
I have no idea what parallel filaments are so Idk if I can use them or not for my amp, or how to learn that information. (I can call the maker of the amp in use but they seem to only say their specific "recommended" tubes and not say what other tubes will safely work)
I compiled this list from various places, many sites or pages I've found have a random one off that the others didn't list.
I've also read sources that limit to only a few tubes:
12AT7, 12AU7, 12AY7, 5751 and 7025 for example.
I am curious if these are all ok to use? Are the sources wrong? Are there more than I've listed? Should I stay away from anything different?
I want to test different tubes for my guitar pre amp and am trying to compile a list of all options.
Follow Ups:
Always wanted to find that unknown '12AX7' for cheap, but everyone seems to know what is what.
Of the ones you have listed only about three are "approximate" replacements to my way of thinking: 12ax7WA, 7025, 5751. The 5751 has lower gain.
The 12BZ7 has very thin mica wafers and is very microphonic. It can be used fixed bias as a diff amp much better than cathode bias or grid leak bias but each triode inside is equivalent to cascoding both sides of a 12ax7 with much more microphonics. You would have to change both the plate and cathode load resistors if you put a 12bz7 in an existing 12ax7 design. It's a vastly DIFFERENT tube! MOEBIAS
"...the fool doth think he is wise but the wise man knows himself to be nothing but a fool." Will Shakespeare
If the voltage and gain are not the same as a 12ax7 then your list is not correct. Here are the tubes that are direct replacements:
ECC83
7025
ECC803
E83CC
6681
CV 4004
That's all folks!
Edits: 09/02/14
The 7058 is a direct drop in. A lot of 7058's are identical to RCA 12AX7. All 7058 tubes were made by RCA.
"What this country needs is a good 5 watt amplifier!" (Paul Klipsch)
A true 7058 is a drop-in 12AX7 replacement in many but not all circuits. One of my favorite tubes, I have 7058s branded RCA, GE, Sylvania, Westinghouse, and Raytheon. If they were all made by RCA, why is the construction different? 'Tis said that many 7058s, and specifically RCA, are actually disguised 12AX7s, in which case they are DEFINITELY drop-in replacements :-)
Because they are not true 7058's. Jim Cross, who is a member of a tube historical group (and a very good tube dealer) provided to me the history of the 7058. He told me that all of the real 7058's were made by RCA. Tubes are well known to be mis-marked on occasion.
"What this country needs is a good 5 watt amplifier!" (Paul Klipsch)
Edits: 09/06/14
Did he also tell you that a true 7058 is a drop-in replacement for 12AX7 tubes in all circuits, in which case I would definitely question his bona fides, at least from what I have read in numerous places.
Edits: 09/06/14
No, he did not. The 7058 does not have a center tap, which means it cannot work in a 6.3V setup. (I) should have made that clear in the original post.:-)BTW, I agree with you on the fact that it is also one of my favorite 12AX7 types.
"What this country needs is a good 5 watt amplifier!" (Paul Klipsch)
Edits: 09/06/14
Yeah, the only problem with 7058s is that they seem to have been "discovered." I used to get sleeves of 5 or batches of 15 on Ebay -- NOS at that -- for under two bucks a tube. Now they go for ridiculous prices. Good thing they're rugged and long-lasting. I gather they were originally produced to serve in car and truck radios, way before the solid state era.
They were indeed designed for mobile applications. The 6681 is another tube that has been discovered. If you look hard, you can still get them for less than 12AX7's
"What this country needs is a good 5 watt amplifier!" (Paul Klipsch)
Thanks, I missed that one.
Some tubes mentioned are not even close (i.e. 12AU7) and can not be considered replacement by any means.
Other than that, circuit would define if other types can be used or not. For example, 12BZ7 CAN be replacement IF the equipment can supply twice the current it requires.
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"One must be sane to think clearly, but one can think deeply and be quite insane."
12AX7 ECC83 ECC803S E83CC 7025 CV4004 CV492 CV4035 M8137 M8214 6057 6681.5751 is close with lesser gain.
Edits: 09/02/14
"Are the sources wrong"
You need to go directly to the source; not rely on the purport of others.
The best way to determine any tube's suitability as a replacement for nother tube is to check the tube manual for the specifications of both. Check to ensure the pin connections are the same, the filament voltage and current are the same, and that the operating conditions are the same. Open the 12AX7 in one screen of your browser and the tube in question in another and compare.
I think you will be quite surprised how far off many tubes in your list are from a 12AX7.
Many of the tubes in your list would be incredibly poor substitutes for a 12AX7.
The 12AU7 is probably the least compatible tube on your list, but I didn't take the time to look up all the unfamiliar ones.
There's also the 7058. Many of those are not exact replacements -- 5751, 12AT7, 12AU7, 12AV7, 12AY7, 7058 (some are closer than others). Unless the manufacturer states otherwise I'd stick with 12AX7/ECC83, 7025, 6681, 7729, 12DF7, 12AD7.
Ok thank you for the replies, I will note the information.
The AU7 is a tube used in the driver stage of this amp so I will stick with that and the 12AX7's.
One thing I did want to double check on is the 12BZ7.
Due to it having higher gain interests me because this is for a pretty high gain guitar amp.
It has a parallel filament. I'm not quite sure what that means, it probably won't work but I'll do more research on that one.
12BZ7 doesn't have higher gain - it has higher transconductance but gain (mu or amplification factor) is 100, same as 12AX7. They are reputed to be quite microphonic, watch out for that. Heater current is twice that of a 12AX7, so it can't be used in a series circuit (as in a Fisher amp or receiver, DC preamp heaters in series). Conversely, the 7058, with no heater tap, can't run at 6.3V but will work fine in a series circuit. (some 7058s DO have the tap connection, though it's not on the data sheet.)
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