Why do old tubes sound better than current tubes?

Tvad, Forgive me for not writing a book about my stuff and tube experience. No one would be interested, even you. Talk about a cost/benefit ratio! :-)

However if I see a post where I can knowledgably recommend a specific new production tube to get a specific result I will do so without regard to whether its old or new. And that is likely the only time I'll ever get into a discussion on the internet about what tubes I like (or not).

I was really doing nothing more than advocating that those who would come here seeking advise take less than very specific advise in response to very specific request with lots of cynicism. A poster should keep a mind open to all possibilities, including that in many applications new (or recent) production tubes can be, or are, as good as he needs in that specific application. IMHO, 'general' rules, broad observations, and general recommendations suck. Now for someone who can't do better than ask for 'What's Best' I'm sure that generic responses would be fine.

BTW, I realize that you have posted that you have not improved on NOS tubes in the applications you have changed tubes in. I take you at your word. But, consider for a moment that this statement really means little beyond the needs of your applications and the number of new (or recent production) tubes you tried as an alternative. Not so many I think IF you have been predisposed to a conclusion based on the age/expense/rarity/ of the tube or the hyper critical application you were using when you reached your conclusion.

Ciao

Tvad, You are right. I did read too much into it I think.

New production (or recent productions) I have found a place for:

SED 6550, SED EL34, SED 6L6GC, and SED KT88's (I really like SED's)

Re-Issue Tung-sol 6550 (in one amp)

JJ and NOS Tesla 6922's and JJ and NOS Tesla 12AX & 12AU7's. I like the NOS tesla's better, but not that much and they are hard to get and can be spendy.

EH6922's (one application so far - not universal by a mile).

Re-Issue Mullard 12AX7's (one application so far)

EI 12AX7E (long grey plate) - my go to NP 12ax7 as a starting point/reference. I really like this particular EI though I guess it is out of production. I've had no QC problems with this one either.
EI 6DJ8 but it is not as quiet or rugged as I like. Again it is no longer in production.
EI 6CG7 - the only new one in production. So far so good but I'm just starting an inquiry into this tube type for a specific amp but so far so good.

And, FWIW, I've got a few others that are still trying to find a good home. Curiosity may have killed the cat - so far I'm only limping! :-)

A question for the assembled experts here with respect to small signal dual triodes.

I'm wondering how significant a variable in all of this gain or gm mismatches between the two triode sections within a tube might be, and if that might account for some of the divergence of experiences with these kinds of tubes.

I recently had occasion to test about a half-dozen absolutely NOS 1950's RCA 5963's (12AU7 equivalents) on my Hickok 800A tester. All of the tubes measured well and matched each other just about perfectly. However, all of them had close to a 20% difference in gm between the two triode sections.

As someone with minimal tube-rolling experience, I'd be interested in comments on how common that kind of difference (or worse) tends to be on both vintage and current production tubes, and on how significant it might be for each of the kinds of circuit functions dual triodes are used for.

Re Grant's question, fwiw I'll mention that in my Paxthon VTA-160 I've just replaced a pair of 1960's vintage used Telefunken 12AX7's, which had measured well until one of them recently developed a problem, and a pair of the NOS 5963's, with matched and balanced pairs of Genalex Gold Lion reissue ECC82's and ECC83's. My early impressions of the new tubes are very favorable, with improved clarity on high volume peaks, and lower noise. (The power tubes I've been using all along are a matched octet of SED "Winged C" EL34's).

Thanks!

-- Al