12ax7 vs 5751

meantime, the sound is still improving on my system so i guess the brimars are still breaking in as they are nos tubes. i still can`t get over the huge difference they`ve made in my system. i`ll update next when the tubes i`ve ordered arrive. the only thing i`m not that thrilled about is the break in time for the black treasures. 300 hours!!! they`ll take forever!!!

Well the good news is they will only sound better as the hours count down. Personally I found with any new tube you need at least 200 hrs before making any judgements.

I have 2 pairs of 5751 RCA and Sylvania, all test very good. I think they are RCA Triple Mica Black Plate, from 1960's.How much do they go for.

I just bought a pair of Rca 5751 triple mica black plates for 70usd. It's my single input tube and I love it. I've read the Sylvania's are supposed to as good but I have no experience with them.

i`m kinda glad too! this tube rolling is getting expensive! i really musn`t order any more!

Oh just wait until you start rolling vintage output tubes or try some current production EAT's!! Then just think of all the combinations with all the input and driver tubes. I just ordered some Gec and Tesla KT88's.

Grayf the Treasure Z's you are getting are supposed to be a very good tube. A big step up from the EH KT88's. Now I'll be honest I don't have or heard the Treasure Z's but from everything I've read they seem to be a step down from the EAT KT88 and a step up from the EH SED and Gold Lion re-issue). I also have a few original Tung Sol 6550 solid black and grey plates. Very different - more seductive and a little less detailed. It just amazes me that I can swap some tubes and change the type of sound. In my PERSONAL opinion the EAT's are the best (won't have the Gec/Tesla for up to couple more weeks to compare). I have a pair and a quad of the EAT's (which I bought used) and after 300 hrs I only have 3 stable tubes. 2 with a bias drift and 1 that puts my Octave into protection mode. So I can make a quad but have to monitor the bias every hour or so.

OK that's the long story - Short story unless there is a real dissatisfaction with the Treasure Z's (very unlikely) just be happy with what you have. You have a lot of combinations of tubes to play with.

Have fun because tube rolling can be a real treat ;)
Disclaimer: I own SED EL34 - 6550 and KT88's Gold Lion reissue KT88 original Tung Sol solid black plates and solid grey plates - EAT KT88 diamonds and Ei KT90's. There is NO bad sounding tubes. Only better sounding ones!!!

Last the Ei KT90's used to be my least favorite output tubes. Only after swapping out the drivers (2 Rca 12at7wa and input 1 Sovtek 12ax7) with Gec CV6091 (military version of the A2900) and Rca triple mica black plate 5751 did I really start to like the Ei's. So I believe with the right combination of tubes anything can be made to sound better :).
So have fun

Grayf I am fairly new to tubes also and enjoy tube rolling a lot. Friday night I had a real big problem. One of my Gec CV6091/A2900's went out and took a Ei KT90 with it (but didn't know it right away). So I replaced the Gec with my Brimar yellow T's and the KT90's with my Tung Sol 6550 black plates. Sat morning I decided to verify the KT90's and sure enough 1 was bad. I didn't know it at the time but when I put the 6550's back in and damn the Brimar took out 1 of my 6550's (all in the same positions). I never thought anything like this could happen. But it did. I have all stock tubes back in now except for my Rca 5751 triple mica black plate. So it was a very sad and more important very expensive weekend for me. I'm still confused because I have had output tubes go before and that was it. Anyhow be careful should an input or driver tube go.

Forgot to mention the lesson I learned is in the future if I have any input or driver tubes go bad to have them checked out with any output tubes in the channel.

What is the difference between 12at7 and 12ax7 ?

I asked Brent Jessee that question but added the 12au7 also. He said the 12ax7 has the highest gain followed by the 12at7 then the 12au7.

+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.