12ax7 vs 5751

Mcpherson -

If you're only considering gain factor, the 12AX7 family falls like this:
12AX7 - 100
5751 - 70
12AT7 - 60
12AY7 - 45
12AV7 - 41
12AU7 - 19

Many circuits can function with any of these, but straying too far from the original gain isn't usually good for the sound. A general rule of thumb would be to substitute as follows:

12AX7 - 5751 / AT7 / AY7
5751 - AX7 / AT7 / AY7
12AT7 - 5751 / AY7
12AY7 - 5751 / AY7 / AV7
12AV7 - AY7 / AU7
12AU7 - AV7

You should always check with your manufacturer. The 5751 and 12AX7 are identical in their limits within a circuit (voltage/amperage) but that's not the case with the others. In most applications you're safe, but you may find it easiest to stick to the 5751 and 12AY7 if you want to try out some different tubes within the family.

+1 Check with the manufacturer first. I have a 5751 in place of my 12ax7 and the manufacturer of my Octave states the 12au7 can be used in place of the 12at7's. So what I have gathered is a lower gain should work in place of a higher gain tube. But I don't think I would want to put in a higher gain tube than what came with it. For the volume differences is so minor it doesn't matter to me. I like the tube that sounds the best.

Now I'll admit I seem to be the oddball here because I've started swapping output tubes before the drivers or input when I got my amp. To me so far the input tube makes the biggest difference in sound.

Xti - The input making a bigger difference than the drivers is a common conclusion. It definitely works that way in my headphone amp.

good info there jazzer, thats something else i`ve learned now.

i`ve found a great tube store here in the uk and the guy is so knowledgeable. karl from karltone. i`ve had a couple of very lengthy chats on the phone with him. i don`t think i`ve ever had a phone chat with a nicer person! he actually recognised and remembered my voice from our previous chat from about a month back! i`ll let you all know how the golden dragon ecc83t`s sound in my system when i get them. probably be at the weekend sometime i`d say.

in the meantime i couldn`t help myself but put the telefunkens back in my amp. i had a good listen last night. the combination of the telefunkens, the brimar 6sn7gty, rca vt231 and the black treasure kt88-z`s are simply mindblowing!!! clarity, depth, slam, punch, warmth, detail, smoothness, imaging, soundstage, realness, it`s all there! this combination picks up on the most subtle of details. i`m not going to say i`m hearing things i`ve never heard before. i will say i`m hearing it all with the greatest of ease. i listened to pink floyds wish you were here cd. welcome to the machine sounds soooo menacing now more than ever! the guitar on shine on you crazy diamond is pitch perfect and this combination of tubes draws out the pure emotion of the guitar not just on that track, but all the way through the cd. ok all of these tubes are pretty pricey, but you gets what you pays for. every cd i play now is more like a journey with this combination of tubes. there`s just 3 or 4 tubes i`ll be looking out for when i have the funds and they are telefunken ribbed plate, raytheon 5751 windmill getter tubes, sylvania 5751`s and if i can stretch far enough i might go for psvanes kt88-t`s. i`m very interested in the raytheon 5751 windmill getter tubes i have to say.

hiya all,

i bought a pair of golden dragon 12ax7`s and finally got them this morning. these are the cheapest by far of all the tubes i have.

i can`t believe i`m going to say this but these have blown everything away! by quite a way too! the lack of noise floor is unbelievable! instruments come out of an inky black background and the imaging is explicit and very very vivid. everything has been pushed forward that comes out of my speakers by quite a way now. the height of the soundstage is natural height, the width goes way beyond the boundary of the side walls and there is an incredible natural sense of depth. but the soundstage is so different from all the rest of the tubes. the images seem to be carved out into the soundstage. the images are razor sharp too. these tubes are extremely explicit in the information they produce. you`re hearing everything in spades! the atmosphere they produce has to be heard to be believed! there`s one aspect of all this that really shocked me was the extra inner detail of every note coming out of every instrument in the soundstage. that blew my mind!!! and it gives the soundstage an extra dimention! it`s more like 4d!

when i mentioned that these tubes are explicit in the detail they drag up, don`t go thinking they`re cold sounding, they have a natural warmth and they are smooth as hell. cymbals sound just like cymbals in all their glory. the extra detail on offer from dave gilmours guitar on the track "where we begin" is nothing short of stunning sounding! extremely expressive! there`s so much more life to everything i hear and everything sounds so natural and real. there`s a natural rawness on offer that gives the sensation of the performer actually standing there in front of you and the same goes for every other instrument in the soundstage. you can pick out any instrument you like in the soundstage and follow it with the greatest of ease and that instrument will be there in it`s own spot in the sounstage with so much air around it. the seperation of instruments is truly jaw dropping! voices sound just about as realistic as you can get!

i have to say the improvement over the telefunkens is stunning and the telefunkens are excellent in their own right. these golden dragons produce a soundstage that is so different from all the other tubes i have heard and they sound so alive.

i cannot believe the difference in sound and for such little money. my system sounds spectacular!