[Mike-48]

I would like to get a spare pair of tubes for my Fet Valve 400R amp. I believe it takes two 12AT7.  Of course AVA sells tubes, but I thought of buying locally. Are there special considerations?  Should the tubes be matched?  If so, is section matching within each tube sufficient, or do the tubes need to be matched with each other?

Thanks!

[Wayner]

I believe they should be a matched set.

Wayner

[tonyptony]

+1. The sections and the pair should be as close as possible, but with any new tubes (especially if they are not the same as what is currently being used) plan to send the amp and the tubes back to AVA to get properly biased. Doesn't really cost all that much and it'll be one thing you won't have to worry about.

[Lefty052347]

Our shop experience would indicate that re-biasing is unnecessary for any standard 12AT7.

However, do buy a matched pair.

Regards,
Dean

[NIGHTFALL1970]

Mike,
I suggest that you stick with JJs.  Frank chose them for a reason.  I have tube rolled a little, and found that I like the stock JJs best.

[tonyptony]

Our shop experience would indicate that re-biasing is unnecessary for any standard 12AT7.

However, do buy a matched pair.

Regards,
Dean

Dean, really? When you guys did my amp with my TFKs Frank did say they biased very close to the stock JJs, but I must have misinterpreted the details to think maybe that was more coincidence than expectation. For people who have (assume well working) tube testers, is there a range of either Gm or section to section balancing (percentage beyond ideal) where you'd say it'd need to be biased for those tubes? Like if the sections are not balanced within (say) 10%, or the Gm is only 80% of the expected as-new value.

[Mike-48]

Guys,

Thanks for the replies!  I suppose I should have expected the diversity of opinion -- which has me wondering if I shouldn't just go back to all-solid-state gear. 

Mike

[aln]

The tubes last a long time so put the best in and enjoy the music.  This is an advantage being able to voice the sound through different tubes.  I use sylvania 6201 gold pin in my two van alstine amps.

[Wayner]

Guys,

Thanks for the replies!  I suppose I should have expected the diversity of opinion -- which has me wondering if I shouldn't just go back to all-solid-state gear. 

Mike

Mike,

These are small signal tubes. They should last for years and years without any need to worry about them. They really don't produce any heat to speak and have a great track record. I suggest buying one extra, matched set pair and put them away (if that makes you comfortable) and forget about worrying about tubes. I went thru the same thing when I got my Ultravalve amp, so I got an extra set of tubes and life is good.

Wayner

[Mike-48]

Thanks again, guys!  Wayner, what you suggest is what I had in mind.  There's probably no chance the venerable 12AT7 will be hard to come by in the future, but I'll rest easier knowing I have a good pair on the shelf.