The Reference 6SN7 Thread

[penger]

Thanks to whoever bumped this! Great read.

[Von Soundcard]

I was referring to usage within manufacturer provided limits (voltage, current) and a usual home operating cycle (6 - 8 hours / day).

I'd like to know if there is a "default" life-span for this type of tubes ('40s-'50s 6SN7, esp. military) - like there is for modern tubes, especially the pro versions.

[sacd lover]

Originally Posted by nick20

I think 1,000-2,000 hours is about the norm, however I don't remember where I read it.

-Nick

Most 6sn7gt's will last around 5000 hours. New production 6sn7 tubes, in general, wont last nearly as long.

[nick20]

Originally Posted by sacd lover

Most 6sn7gt's will last around 5000 hours. New production 6sn7 tubes, in general, wont last nearly as long.

Who logs their hours anyways!? I just listen..


mmm.. music..mmm

[Von Soundcard]

It's important when you buy tubes, if it lasts half the time you buy twice the tubes

I am mostly interested in old tubes ('40s-'50s), esp. military versions. That figure of 5000 hours sounds really good. However does it represent the time until they start to degrade their sound quality substantially OR the time until they fail completely ?

[nick20]

Originally Posted by Von Soundcard

It's important when you buy tubes, if it lasts half the time you buy twice the tubes

I am mostly interested in old tubes ('40s-'50s), esp. military versions. That figure of 5000 hours sounds really good. However does it represent the time until they start to degrade their sound quality substantially OR the time until they fail completely ?

5,000 hours will last you almost 3 years, if you listen to it for 5 hours a day. That's a lot of listening.




-Nick

[Hirsch]

Originally Posted by Von Soundcard

I am mostly interested in old tubes ('40s-'50s), esp. military versions. That figure of 5000 hours sounds really good. However does it represent the time until they start to degrade their sound quality substantially OR the time until they fail completely ?

In the absence of information about the circuit you are running them in, the 5000 hour figure doesn't mean anything. A tube life rating makes assumptions about how hard you are driving the tube. A circuit that is easy on the tubes can extend their life significantly. One that is hard on the tubes will chew them up and spit them out.

[nick20]

Originally Posted by Hirsch

In the absence of information about the circuit you are running them in, the 5000 hour figure doesn't mean anything. A tube life rating makes assumptions about how hard you are driving the tube. A circuit that is easy on the tubes can extend their life significantly. One that is hard on the tubes will chew them up and spit them out.

Very well said.


I will end up buying a duplicate of the tubes I like anyways, so if something DOES happen, I have another one handy. Or I'll buy in pairs, if I can.

[tourmaline]

Originally Posted by nick20

Very well said.


I will end up buying a duplicate of the tubes I like anyways, so if something DOES happen, I have another one handy. Or I'll buy in pairs, if I can.

Concerning this:


To ensure good tube reliability you should probably run a tube at 70% or less of its maximum plate dissipation.

Using the general audio application of 250 plate volts, a bias of 8 volts resulting in 9ma of current and plate dissipation of 2.25 Watts, we find:

5692 - runs 43 % over maximum rating – It isn’t a 10,000 hour tube when you run it this HOT!
6SN7GT - runs 64% of maximum – coasting and liking it
6SN7GTA/GTB - runs 45% of maximum – Hardly turned on, may outlast you.

The older tubes probably burn faster then the newer type tubes.

Most jan or w designated tubes have 10.000 hours of life, minimum of at least 5000 anyway.

[nick20]

Originally Posted by tourmaline

Concerning this:


To ensure good tube reliability you should probably run a tube at 70% or less of its maximum plate dissipation.

Using the general audio application of 250 plate volts, a bias of 8 volts resulting in 9ma of current and plate dissipation of 2.25 Watts, we find:

5692 - runs 43 % over maximum rating – It isn’t a 10,000 hour tube when you run it this HOT!
6SN7GT - runs 64% of maximum – coasting and liking it
6SN7GTA/GTB - runs 45% of maximum – Hardly turned on, may outlast you.

The older tubes probably burn faster then the newer type tubes.

Most jan or w designated tubes have 10.000 hours of life, minimum of at least 5000 anyway.

I posted a link to that info. I've read it before.

5692's are mostly for low watts, because it runs 43% over maximum rating. The normal rating for a 5692 is 1.075 watts, in order to "maintain" the 10,000 hour rating it must be used in low wattage amplifiers.

Most tubes will last you longer than a year, in which I recommend picking up a duplicate, just in case.





-Nick