How long do tubes last ?

[251]

Did'nt really see this in the Amps FAQ ( the subject, printed in blue, means it is being edited ), so I wonder if we could get some views. I recently mentioned in the Portaflex thread that I was going to replace the tubes in my '67 B15N, and got some discussion going about why I was even considering it, to the difference in some brands of tubes for the same model. But what I'm really wondering is, how long do tubes in a bass amp usually last, and how do you know when to change them? Should they be changed as a set, or individually as needed? I was told that some guys have tubes in their amps that are 40 years old, and don't see the need to get new ones, or NOS tubes. My guitar player ( Fender Super Reverb ), changes them every 5 years or so. So, what do you think about the life of tubes, when should they be switched out for new, or NOS models, or, are they good until they finally die? What about new as opposed to used, or NOS tubes? Anything else you want to add, feel free.

The answer(s) are buried in this thread on CR4, an engineering forum;

Invalid Link Removed

Keep that home light burning in your chassis.

 

[coreyfyfe]

When I bouth my Portaflex, it had a modern set of JJ's for power tubes and a hodgepodge of brands for the preamp tubes. Just for kicks, I scrounged Ebay and other places looking for Ampeg Branded Sylvanias like what would have been stock in the amp. I eventually found some, and I swapped them out. Even though they are all "old tubes" and certainly weren't NOS, they sound excellent.

Even NOS isn't all it's cracked up to be. When I bought my first B15 it came with some odd-ball brand of 6SL7s, some really old 6L6GCs, and a Ruby 5AR4. He also threw in some random other tubes he had just laying around in boxes that he thought belonged to the amp. Turned out, the original Ampeg branded 6SL7s were in those boxes, which was good because one of the odd-ball tubes was pretty noisy. Swapped em out, popped in some JJ 6L6GCs and a new 5AR4 (I was buying new power tubes so why not right?) and it sounded fantastic. Whatever info I could gather on the odd-ball tubes (I've forgotten the name already, it hasn't even been 2 years....) was that they were a brand in the 70s or 80s.

Similar story, I retubed my V4 top to bottom when I got it, all the preamp tubes were old - some might have been original, they were sylvannias - with a set from fliptops which included a NOS RCA for one of the tubes. Darn thing went bad a few months later. It was whistling pretty good. Gave it the chopstick test and it sounded like I was pounding on the walls. Swapped the one that came with the amp back in there and it was good to go.

 

[ajunea3]

preamp tubes are one thing, but for power amp tubes, it depends on how hot they've been biased in the amp. some prefer a hotter bias resulting in a growlier, quick to overdrive, sizzly tone, but this can also quickly shorten the life of any power amp tube.

From what I've read on Ampeg's website, it's the OVER-biasing of tubes that causes quick tube saturation and early distortion, which results in LONGER tube life span. Conversely, when you under-bias tubes, you get a bigger fatter sound, which shortens the life span of tubes. So if you like you amp hot and growly you're actually doing yourself a favor and lengthening the average lifespan of the tubes. Someone correct me if I'm wrong.

 

[seamonkey]

Ampeg and other amp manufacturers publish different information than usually given in the forums. There's plenty of anecdotal evidence in forums, and plenty of online vendors selling tubes. You can find copies of old mil-specs that list expected tube life for tubes that were used in the military.

You decide yourself. Either learn about tubes, or find a good tech you can trust.

What Ampeg publishes in one case:
[Invalid or Expired Link Removed]

"The Nature Of Tubes: Why (And When) To Replace Them:
Tubes are made up of a number of fragile mechanical components that are vacuum-sealed in a glass envelope
or bubble. The tube's longevity is based on a number of factors which include how hard and often the
amplifier is played, vibration from the speakers, road travel, repeated set up and tear down, etc.
Any time you notice a change in your amplifier's performance, check the tubes first.
If it's been a while since the tubes were replaced and the sound from your amplifier lacks punch, fades in
and out, loses highs or lows or produces unusual sounds, the power tubes probably need to be replaced. If
your amplifier squeals, makes noise, loses gain, starts to hum, lacks "sensitivity", or feels as if it is working
against you, the preamplifier tubes may need to be replaced.
The power tubes are subjected to considerably more stress than the preamplifier tubes. Consequently, they
almost always fail/degrade first. If deteriorating power tubes aren't replaced they will ultimately fail.
Depending on the failure mode, they may even cause severe damage to the audio output transformer
and/or other components in the amplifier. Replacing the tubes before they fail completely has the potential
to save you time, money and unwanted trouble. Since power tubes work together in an amplifier, it is crucial
that they (if there is more than one) be replaced by a matched set. If you're on the road a lot, we recommend
that you carry a spare matched set of replacement power tubes and their associated driver tubes.
After turning off the power and disconnecting the amplifier from the power source, carefully check the tubes
(in bright light) for cracks or white spots inside the glass or any other apparent damage. Then, with the
power on, view the tubes in a dark room. Look for preamplifier tubes that do not glow at all or power tubes
that glow excessively red."

 

[JimmyM]

Ampeg and other amp manufacturers publish different information than usually given in the forums. There's plenty of anecdotal evidence in forums, and plenty of online vendors selling tubes. You can find copies of old mil-specs that list expected tube life for tubes that were used in the military.

You decide yourself. Either learn about tubes, or find a good tech you can trust.

What Ampeg publishes in one case:
[Invalid or Expired Link Removed]

"The Nature Of Tubes: Why (And When) To Replace Them:
Tubes are made up of a number of fragile mechanical components that are vacuum-sealed in a glass envelope
or bubble. The tube's longevity is based on a number of factors which include how hard and often the
amplifier is played, vibration from the speakers, road travel, repeated set up and tear down, etc.
Any time you notice a change in your amplifier's performance, check the tubes first.
If it's been a while since the tubes were replaced and the sound from your amplifier lacks punch, fades in
and out, loses highs or lows or produces unusual sounds, the power tubes probably need to be replaced. If
your amplifier squeals, makes noise, loses gain, starts to hum, lacks "sensitivity", or feels as if it is working
against you, the preamplifier tubes may need to be replaced.
The power tubes are subjected to considerably more stress than the preamplifier tubes. Consequently, they
almost always fail/degrade first. If deteriorating power tubes aren't replaced they will ultimately fail.
Depending on the failure mode, they may even cause severe damage to the audio output transformer
and/or other components in the amplifier. Replacing the tubes before they fail completely has the potential
to save you time, money and unwanted trouble. Since power tubes work together in an amplifier, it is crucial
that they (if there is more than one) be replaced by a matched set. If you're on the road a lot, we recommend
that you carry a spare matched set of replacement power tubes and their associated driver tubes.
After turning off the power and disconnecting the amplifier from the power source, carefully check the tubes
(in bright light) for cracks or white spots inside the glass or any other apparent damage. Then, with the
power on, view the tubes in a dark room. Look for preamplifier tubes that do not glow at all or power tubes
that glow excessively red."

thank you for the "never touched a tube amp in my life" opinion.