[woktrr1919]

Hey all,
 
I'm a bit of a newbie to tube amps, and am trying to get as educated as possible on all aspects of the technology. One thing that has me a bit confused is purchasing replacement tubes to roll. More specifically, the topic of NOS tubes (new old stock I believe?)
 
My understanding is that NOS tubes are tubes that were built several decades ago that are no longer in production, but were never used. In my search for some backup 6AK5 preamp tubes, it seems like the only ones I can find are the NOS tubes. Is this pretty standard when purchasing tubes? My only concern is that they're going to be so old, that they might have deteriorated to the point of not working as well as they should. I can't seem to find any tubes with a more recent production date. Do manufacturers just not make them any longer since they're seen as obsolete?
 
Like I said, I'm new to tube amps so these fears might be completely unnecessary; I just wanted to get the input of some of the more seasoned listeners out there.
 
Thanks!

 

[kramer5150]

FWIW I've been really lucky with my NOS and even used tube purchases.  A lot of www and e-pay sellers test and state test result numbers too.   Its kind of based on the honor system there where you're relying on the integrity of the seller.  For that I stick with sellers with a good reputation, ebay or otherwise.
 
I dont do any kind of elaborate test either when I get em.  I just plug them into my amp, watch things carefully and give it a koss KSC75 impedance load (cheap+expendable)  and let it run for a couple hours.

 

[wuwhere]

New old stock (NOS) tubes are old tubes that have not been used and therefore are considered new. As far as I know, they don't deteriorate inside since it is a vacuum. The pins can tarnish but can be cleaned. New tubes are still being made mostly by Russians and Chinese companies. These are called reissues. They are mostly the popular tubes like 12AX7, KT88, 6550, etc...
 
There are newer output tubes that have been developed recently like the KT90s and the newer KT120. So you won't find NOS of these tubes, though the Ei KT90s are sought after for their sound and reliability.