life of stock tubes (and where to get backups)

[denti alligator]

I use my SEX w/ C4S about 1-3 hours per day, at about 1,000 hours a year. How long will the tubes last me, approximately, and where can I get replacement backups?

[Grainger49]

There is always ebay.  You might get a good NOS pair and might get a worn, NOS looking pair.  I think that is the problem there.

There are a number of sellers.  Two I have used are Tube World and Upscale Audio.  What you get from a dealer well known like these two is confidence that the product is what you expect.

As for tube life I have seen numbers like 5,000 hours and 10,000 hours.

[Paul Birkeland]

How long will the tubes last me?

I'd say at least 10,000 hours, and perhaps closer to 50,000.  Hopefully PJ will chime in, he has a SEX amp is his AV system that has been running daily on the same tubes since he built it!

[Paul Joppa]

Actually, I have the original prototype, from 2004. I suppose it gets 2-3 hours use per day, so that's about 7500 hours so far. It still works just fine.

The spares I have on hand have never been used, but I got them from Antique Electronic Supply. Nothing special, just whatever they had in the warehouse. <goes and looks> they are GEs and RCAs. Still in their boxes.

[jamestw]

............................ and where can I get replacement backups?

BottleHead.com , obviously.

:-)
james

[Natural Sound]

The 6DN7 was designed for use as a vertical deflection oscillator/amplifier in a TV circuit. Its a very tough tube that can take a fair share of abuse. I would imagine that the operating points that PJ and Doc chose in the S.E.X. audio application is much less demanding. Consequently tube life should be quite good. I built my S.E.X. amp in 2005 and the original tubes still test good on my B&K 707 tube tester. I use mine a couple of hours a day, more on the weekends. I originally figured that I'd be changing tubes every couple of years. I was wrong, very wrong.

I bought a couple of NOS sleeves (5ea) pairs from a dealer as backups. That should be enough for my lifetime and then some. Keep in mind though that a lot of these tubes are more than 45 years old. I have some other (non 6DN7 tubes) of WWII vintage that are closer to 70 years old and still work fine. But you never know when one will decide to retire for good. Having backups is a good idea, within reason. Some people go a little overboard.

[Paul Joppa]

Actually, we run the power section at 10 watts, which is the rated maximum. I think these TV tubes were intended to operate in a very hot environment (20 or 25 tubes in a color TV), with tough electrical conditions (the vertical output has some fierce voltage spikes at every frame), and high reliability was important.

Both Dave, who first thought of using this tube, and I, when working on the stereo version made the same mistake - reversed the driver and power sections. It works fairly well and sounds pretty good - and the driver section, rated 1 watt, is operating at about 6 watts! The plate glows a dull orange, which is how we figured out the problem, but it does show how tough they are. No transistor would last even a fraction of a second under those conditions.

[Grainger49]

Now that is funny, mostly because I can see me doing the same thing.

[Paul Birkeland]

I think these TV tubes were intended to operate in a very hot environment (20 or 25 tubes in a color TV), with tough electrical conditions (the vertical output has some fierce voltage spikes at every frame), and high reliability was important.

Yeah, I use some compactrons where one section is "equivalent" to half of a 12AT7, the plates in that section are gigantic, it'd be hard to beleive you couldn't push it quite a bit harder!