SVT3pro tubes...

[jvanick]

I'm retubing my svt3pro to get it ready for my backup rig/small gig/home practice setup..

the tubes are probably a minimum of 10 years old if not older, so I feel it's time.

I read that it takes 4 12AX7's and 1 12AU7...

well, opening it up, there are 2 unlabeled tubes in there which to the eye look identical...

the front 3 are all the same and labeled Sovtek 12AX7-WB

the back 2 are different than the front 3... I'm wondering if my unit was put together with dual 12AU7's ?

Here's the rear tubes that I'm talking about:



Here's all the tubes...

[warnergt]

[JimmyM]

i've had tubes last decades. if it ain't broke, don't fix it.

[RickenBoogie]

+1 there's absolutely no reason to change those preamp tubes, unless they ain't working. Decades, easy. People always assume because they're old, they must be bad. Not true.

[main_sale]

Yeah, preamp tubes can last for 50,000 hours and that is a very long time!

[jvanick]

Cool! Thanks for saving me a few $$$... The amp sounds great now, so it's good to know that I don't have to really do much.

anybody have any feel for the fact that it looks like I have a pair of 12au7's in the back 2 sockets instead of a 12ax7 and 12au7?

-J

[derridiandrift]

If I'm not mistaken, a 12AU7 will have a bit lower gain than a 12AX7. If you have a 12AU7 in a 12AX7 slot (and the amp is otherwise working fine) you're getting less gain in that place on the circuit, which often translates to more clean headroom. Not a bad thing unless you're after more gain. If you like the sound of the amp the way it is, close the lid and forget about it.

I currently have some 12AX7 tubes in the front end of my SVT-VR that came out of a dead Traynor YBA-1 from the 60s. Nice quiet tubes that are much older than your Sovteks.

[derridiandrift]

I just re-read your post and noticed that the back two tubes are not labelled but they look the same. I'm not sure that the difference between a 12AX7 and 12AU7 are always discernible by looking at them.