The 12AT7 is interchangable with the 12AX7, but has slightly more than 30% less gain. ergo: You will have to turn the volume a bit higher to get the same SPL from your system. |
Dropping a 12AT7 in for a 12AX7 does more than reduce gain. The cathode and plate resistors should be changed to make the 12AT7 operate in the most linear fashion. The two tubes have very different transconductance and plate resistance. |
"The 12AT7 is interchangable with the 12AX7, but has slightly more than 30% less gain"
Rodman - I've heard that about the 12AX7 vs. the 5751, but never the 12AT7. Are you sure you're on track with this? |
Sebrof- I guess I WAS off a bit. the 5751 is 30% reduction in gain. These sites have the difference as 40% less for the 12AT7: (http://thetubestore.com/gainfactor.html) (http://cydathria.com/fdm/12AX7_sub.html) and(to me at least)that seems greater than, "slightly more" of a difference(my bad). Both sites mention that the tubes are interchangable. The first site: that they are, "plate voltage compatible". |
My thanks to all. I guess my question then is what Gmuffley is stating. I don't want to change components and don't want any damage to boot. I'll check the links given by Rodman99999 and go from there. |
A follow up with the 12at7 tubes: I have a pair of Tungsram tubes that I brought for a VTL pre that was sold. I kept the tubes so hence the post. Installed them this afternoon (replaced a pair of Tungsol) and WOW. No difference in gain to my ears and the sonics of the Tungsrams walk all over the Tungsols. The battle of the T's should be the title of this post. : ) Thanks again to all. |
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This is good to know.
I have an amp coming that uses 12AX7s. I do have some better 12AT7s that I'll investigate dropping in. I didn't know that ATs and AXs were interchangeable. (I do have 5751s coming as well). |
Sebrof let us know what you think when you get them installed. |
Just got the amp and tubes yesterday. I'm breaking in the power tubes, the 5751, and amp before I start rolling. I'll try to remember to post back in a few days. |
12AT7 and 12AX7 are NOT "interchangable." |
Thanks Doak.
So much for that experiment. |
I beg to differ. The links given do state that these tubes are interchangable. I have done this as mentioned in my setup with no ill effects. Of course Sebrof the decision is your call. Good listening. |
Actually, there are some semantics involved, as the 12AX7 can be replaced with a 5751, 12AT7 or 12AY7, but the 12AT7 can only be replaced with a 5751 or a 12AY7. ERGO, "interchangeable" may not be the correct word. |
Rodman or anyone else, have you actually substituted 12AT7s for 12AX7s or other swaps mentioned in the links?
It would be great if we could swap tube types but the Tube Store writeup says:
"These substitutions can also work in home audio amps, but we don't recommend trying this unless you are having trouble finding the correct tube type for your amp." |
Yes- and for decades. Guitar, microphone pre, and home audio amps. The AT's are usually slightly less microphonic/noisy, and sometimes it's nice to have less gain in a driver stage. The 6201 tubes are especially nice in that(quietness) regard. I don't have anything presently, that uses the AX family, but not much has changed in tube circuit topography(input/phase splitter/driver stages) in the past 40 years(how long I've been paying attention), outside of the quality of the parts used in construction. I do have a pair of gold pinned, triple mica 6201's, left over from an amp that I was building, if anyone would like to try them(free). |
Hi Rodman99999,
Thanks for your added comments. As stated I have replaced a pair of AX for a pair of AT's with no ill effects other than the lower gain. Tell me more about the 6201 tubes as I don't have knowledge about them. Will they work in place of the AX family? |
Hi South43- A quote from a tube site: "6201- Usually appears along with 12AT7WA designation (military version) on the same vacuum tube. However, some tube makers made commercial versions of a 6201 as an "industrial" 12AT7. Sylvania made a 6201 vacuum tube in their Gold Brand line, and it came in gold boxes, gold silk screen on the glass, and most had gold plated pins. Amperex's PQ version of the 6201, also known as a E81CC with gold pins usually made in Germany or Holland.. Earlier USA made 6201 as well as the european made 6201 vacuum tubes, often have an extra mica spacer on top. These are also known as "triple mica", and are usually very quiet and well suited for hifi audio applications. Overall, the 6201 is a huge upgrade over a standard 12AT7, and were designed to meet military specs with critical applications." This site has some pics: (https://www.tubeworld.com/12at7.htm) |
Hi Rodman99999,
After I posted my question to you I checked on the 6201 tubes and did find the comaprison to the 12AT7. I went back to the Tungsol 12AX7's made for my pre and was pleased with what I heard. Though I thought the Tungsram 12AT7's had better detail it was the gain I missed as you know is less that the 12AX7's. I'm curious as to what the Sylvania would sound like in comparison to the Tungsram tubes I have. Know doubt the gain isssue would rear it's head but----. Have you compared the Sylvanias to any other 12AT7's? I'll be checking back later today. |
The ones that I have are actually labelled, 'Telefunken' but were obviously made by someone else(no diamond on the bottom). I never had another tube in the amp, and so- have no valid comparison. The mention of Sylvania's 6201 was part of the quote, and general info, from that site. Sorry if it misled you. |
No worries Rodman99999. Not to change the subject but I posted a thread in reference to a cap upgrade for my symphonies pre. Any suggestions? |
