[Calypte]

Yes, I've looked at Frank's past comments on this, but I couldn't find an answer to this question: regarding the 12AT7s used in the FET Valve amps, what is your gut feeling about the continued availability of these tubes?  Is their use so widespread that they'll always be available ("always" = ~ 25 years for me, probably).  Or are they made only in one small factory by one 90-year old guy in the Urals, and when he's gone, they're gone?

[trebejo]

The 12AT7 looks like a pretty popular tube... in general, AVA stays away from unusual tubes. One of the motivations for the original ST70 mods by Frank was to get away from the 7199 input tubes, which were to become scarce with time.

Now, which 12AT7, that's a different conversation, better talk to Frank about that one because sometimes the amp has to be rebiased if you switch brands.

[martyo]

I have a Double 550+. I'm using Telefunkens from 1967 and have a back up pair. I also have a quad of Seimens from 1966. All those tubes are at the mininum 10,000 hours. One can't see 25 years ahead, but these days there continues to be more tubed gear and the 12AT7 is a very common tube. My crystal ball says.......

[Ericus Rex]

There are more active tube manufacturers now than 20 years ago.  Can't say what'll happen in 25 years but I'm sure the guitar guys won't be giving up their tube amps anytime soon.  One could argue they were the only ones keeping the tube business going in the 80's and 90's.  Since tube guitar amps far outnumber home tube equipment they will keep the tube market alive, IMO.

[Minn Mark]

I'm no tube expert, but I think the Czechs are making some pretty darn good ones. The larger power tubes (EL34, 6550, etc) I think will be around a long time, given their popularity in music amplifiiers. My Savage Audio guitar amp uses 4 EL84 Power Tubes, 3 12AX7 Preamp Tubes, 2 12AT7 Preamp Tubes, 1 5AR4 Rectifier Tube.

shameless plug:

www.savageamps.com

[Calypte]

Thanks.  I'm a classical music fan and know nothing about guitar amps.  But if the 12AT7 tubes are used there, then their continued availability is probably safe for a long time.

[Brett Buck]

Thanks.  I'm a classical music fan and know nothing about guitar amps.  But if the 12AT7 tubes are used there, then their continued availability is probably safe for a long time.

   If you are worried about it, hoard them like everybody else. 12at7s are cheap, they generally last a long time (say, 5 years on the low end), so if you buy $200 worth today you will be set for something like 50 years, bare minimum. And that's grossly conservative because some will crap out in a few months and others will outlive cockroaches.
 
    I have a bunch of small-signal and rectifier tubes that are on the order of *70 years old* and they work just fine, even the crappy 1.4 volt filament Loctal radio tubes that weren't very good in the first place.  In fact I have a bunch of old radios in the range of 50 to 75 years old that use *many* original tubes; it's actually quite rare to find a bad one.

   Tiny amount of money by audiophile standards will get you hip-deep in replacement tubes.

      Brett

[heiba]

From a web forum:

"Many of the tube production machines and tools of Telefunken went to the Eastern bloc when tube production became unprofitable in the Western world. Some were scrapped. Some vintage Tesla tubes are just like Telefunken. Tesla got those machines, I am not sure about EI. The Tesla tube production company is now called JJ Electronics and they produce a ECC83S tube which is very good. Note the S. This tube is the equivalent to 12AX7." (petzi)

Ola

[martyo]

From a web forum:

"Many of the tube production machines and tools of Telefunken went to the Eastern bloc when tube production became unprofitable in the Western world. Some were scrapped. Some vintage Tesla tubes are just like Telefunken. Tesla got those machines, I am not sure about EI. The Tesla tube production company is now called JJ Electronics and they produce a ECC83S tube which is very good. Note the S. This tube is the equivalent to 12AX7." (petzi)

Ola

My own personal experience doesn't track with "a web forum". Just talking small signal tubes, not power tubes. I have current production JJ AT7's and the real Telefunkens. Not even close.

[heiba]

Thank you - nice to know.

Ola

[Listens2tubes]

My own personal experience doesn't track with "a web forum". Just talking small signal tubes, not power tubes. I have current production JJ AT7's and the real Telefunkens. Not even close.

+1

[Brett Buck]

My own personal experience doesn't track with "a web forum". Just talking small signal tubes, not power tubes. I have current production JJ AT7's and the real Telefunkens. Not even close.

    If someone is claiming that the JJ is identical to a Telefunken 12AX7 and made on the same machines, that's clearly incorrect. If nothing else the plates are around half the total length. Performance wise, near as I can tell, the JJ is equal or superior. And not nearly as microphonic. The one problem I have is that the infant mortality is absurdly high. But once I got some that worked for the first few months they kept working for 4-ish years later.

    I have lots of Telefunkens but they are sitting in my gigantic tube case (in another 10 years they will be more absurdly overpriced than they are now) and JJs are in equipment. 

    Brett

[Listens2tubes]

Hmm ... tubes as an investment I guess we'll see what Mullard EL34 xf2 quads are worth in ten years, since the late model Genalex KT-77's are sounding superb, while the xf2's languish in a box. As for a 12AT7's the Tele ECC801S trounced the JJ's thin lifeless sound. Best things I ever heard in the small chasis T8 linestage.

As an aside: If the equipment is working and designed well tube life can be extremely long. Some old Dyna and Fisher as well as vintage radios still run with the original tubes in homes of the original owner/user.

[SteveFord]

Right now I'm listening to a Sherwood tuner (1962-ish), it's fresh out of the shop for a going over and alignment and it's had ONE tube replaced - all of the others were within spec.
Tubes can last a very long time.

[Calypte]

Right now I'm listening to a Sherwood tuner (1962-ish), it's fresh out of the shop for a going over and alignment and it's had ONE tube replaced - all of the others were within spec.
Tubes can last a very long time.

Decades ago, I owned an Eico ST-70 integrated amp.  It seemed to me the tubes died rather quickly.  I know I replaced the output tubes at least once in the four or five years I used the amp.

[rcag_ils]

Decades ago, I owned an Eico ST-70 integrated amp.  It seemed to me the tubes died rather quickly.  I know I replaced the output tubes at least once in the four or five years I used the amp.

I have an Eico St-70, big heavy transformers. I don't use it much so I can't say how long the tubes will last, but I've stocked up many sets of spare for it just in case.

[Calypte]

It's possible, very deep in my old papers, that I still have a McIntosh amplifier test chart for my Eico ST-70.  IIRC, the HD graph looked a lot like that for the Dynaco ST-70.