[Doublej]

How does one know when it's time to replace a tube?

I have a 15+/- year old Assemblage L-1 single tube amplifier that still has it's original tube. It's left in standby mode when I am not using it.

[FullRangeMan]

My 2 cents:
On output tubes the bass will become soft, frail, sometimes it dont keep Bias anymore.

[geowak]

I think that is the whole point of a tube tester. Tubes lose life over time and a tester can determine if it has a short or what the remaining life should be.

[WireNut]

DoubleJ,

I have an SFL-2 which uses 8 6DJ8/6922's. If one tube is noisy it makes my tweeter(s) hiss or pop. At that point its time to find out which tube is the culprit by tapping on them. The tubes used in the cathode follower positions can be anything and really don't seem to benefit from high dollar tubes in my experience. As long and they are quite, I'm happy. Tubes in the cathode follower positions don't even have to be matched in my experience..... It's the gain tubes that are the most important........

I use two Siemens 6922'S as gain tubes, and anything (not even matched) that keeps my preamp quite in the cathode follower positions. Sounds balanced and quite as can be but took some tube rolling in the cathode positions to make it dead quite........

[Ericus Rex]

Wow!  15 years on a single tube is awesome!  Most of mine go noisy after only a couple of years.   No doubt your use of standby mode has helped you achieve this life.  You've been very lucky.

If they don't prematurely fail or go noisy, those 9 pins used in preamps and driver positions should last 10,000 hours. This is not the case for power tubes.  In a good design you can expect half those hours at most.  (yes, there are exceptions but I think this is the general lifetime to expect in a conservative design).  So depending on your listening habits, you may be approaching 10K hours on that tube.  This doesn't necessarily mean you need to replace it.  It may last another 10 years...who knows.  Does your system still excite you the way it did 10 years ago?  If you think your sound has lost some sparkle or the dynamics sound a bit 'muted' then the tube may be worn out.  Is the L-R balance still even?  If you answered 'yes' to both questions then your tube is probably still good.  If it keeps you up at night thinking about your tube life than go ahead and get a replacement.  New production tubes are cheap enough for you to get one and see if your sound changes drastically.

Keep us informed!

[Freo-1]

Given the fact that the original tube has 15 years on it, you may want to get a spare and throw it in there just to see if you notice a difference.  Since you have a 6DJ8, one sub tube to consider is a 7DJ8.  They are a bit lees cost wise, well made, and will generally work fine in audio amps.  See  if you find a buddy who has a tube tester that measures gm.  That way, you would know how much life is left in your tube.

An interesting factoid:  Some pencil tubes, such as the 6111, were designed to last 100,000 hours!  Quad uses a single 6111 tube in one of their preamp models.

[WireNut]

DoubleJ,

Just walked up to my loudspeakers. They are both dead quiet now. What it took was replacing one noisy tube per channel in the cathode positions.. Dead quiet, so happy...Sounding amazing and balanced even without matching tubes in the cathode follower positions....Put your money in the gain tubes.... Use quiet/cheaper tubes in the cathode stage.......

[Doublej]

You guys have me convinced it's time to replace the tube, now how do I pick a make and where's a reputable place to buy it?

[SteveFord]

Why not contact Parts Connexion up in Canada and ask them what they've got for you?
http://www.partsconnexion.com/