Tube lifespan in a tube chip-amp?

[tomkatt]

Just curious, what's the lifespan of a tube before I should replace it? And are there any indications when a tube should be replaced? I've been using an Aiyima T9 for daily listening for the last nine months and not sure at what point the tubes may need replacing, since it doesn't work without them. I assume it's in the range of several years, but I honestly don't know, never owned a tube amp before.

 

[Keith_W]

A typical valve will last between 5,000 - 20,000 hours. Factors that shorten the lifespan of the tube may include improper manufacturing, turning it on and off very often, and overdriving the valve. If the valve is improperly manufactured, it may leak vacuum. The barium/magnesium getter (the silver flash on the inside of the tube) absorbs air molecules and helps mitigate this. If it loses vacuum you will see that the getter will oxidize - it won't be shiny silver any more, and it may turn white.

Symptoms of a dead or dying tube: a crackly, hissy sound from your speakers, one tube glowing dimmer or brighter than the other, and low volume. If you have a non-auto biasing amp (i.e. you bias the valves with a meter), you may notice that you have to keep increasing the voltage to re-bias the amp.

The only objective way to find out if a tube that does not manifest those symptoms is dying is to use a tube tester. It is likely that nobody you know owns one, so you have to seek out an audio engineer who is able to test tubes for you.

 

[JeffS7444]

Just curious, what's the lifespan of a tube before I should replace it? And are there any indications when a tube should be replaced? I've been using an Aiyima T9 for daily listening for the last nine months and not sure at what point the tubes may need replacing, since it doesn't work without them. I assume it's in the range of several years, but I honestly don't know, never owned a tube amp before.

Lacking a tube tester, I suppose I wouldn't worry about it unless it seems to be becoming noisy or microphonic. Given the application (likely a unity-gain buffer), it could possibly last for the lifetime of the device. In my tube-o-phile days, the tubes that needed the most frequent replacements were rectifiers and power output devices.

 

[egellings]

A typical valve will last between 5,000 - 20,000 hours. Factors that shorten the lifespan of the tube may include improper manufacturing, turning it on and off very often, and overdriving the valve. If the valve is improperly manufactured, it may leak vacuum. The barium/magnesium getter (the silver flash on the inside of the tube) absorbs air molecules and helps mitigate this. If it loses vacuum you will see that the getter will oxidize - it won't be shiny silver any more, and it may turn white.

Symptoms of a dead or dying tube: a crackly, hissy sound from your speakers, one tube glowing dimmer or brighter than the other, and low volume. If you have a non-auto biasing amp (i.e. you bias the valves with a meter), you may notice that you have to keep increasing the voltage to re-bias the amp.

The only objective way to find out if a tube that does not manifest those symptoms is dying is to use a tube tester. It is likely that nobody you know owns one, so you have to seek out an audio engineer who is able to test tubes for you.

You could also keep a set of new spare tubes handy, and if you think a tube in the equipment is failing, a quick substitution from the spare ones will answer the question for you.

 

[JDKinase]

FWIW, I recently tested the tubes on the 1960’s McIntosh amp/preamp I inherited from my father. Original Telefunken and RCAs tested OK, I replaced with NOS “just because”. Some amps are more gentle on tubes, so YMMV.

 

[mhardy6647]

"small signal" tubes have very long lifespans when used in accordance with their design limits.
The design limits are readily available for most common tubes in RCA's fine series of Receiving Tube Manuals.
Many different volumes thereof are easily available as (searchable) PDFs from the magnificient resource that is World Radio History.
Just go here and scroll down to the "Rs".

BOOKSHELF RCA: Radi Corporation of America tech guides

BOOKSHELF RCA: Radi Corporation of America tech guides

www.worldradiohistory.com

As an aside: the temptation to abuse tubes will be more typically found in power output sections. In the 1990s there was a company called Golden Tube Audio which was notorious for the short lifespan of certain tubes in their amplifiers... due to the unsavory operating points they chose to use.

PS the best tube test for most tube types is the in circuit use test. A properly calibrated transconductance type tube tester is invaluable for matching output tubes' operating characteristics (when that is necessary). Simple emissions-type testers do have their value, mostly for identifying grid leakage or shorts in a questionable tube. Full disclosure: the only tube tester I own is a simple but reliable Sencore Mighty-Mite emissions tester which was my father's daily driver for decades . It is "fit for purpose".
If I need to test a tube under actual operating conditions, I do know folks with proper transconductance testers. You might be surprised how easy it might be to find someone with a tube tester in your region. Look for amateur radio clubs or fleamarkets and ask around.