Longevity of EH tubes?

[Dr. Toobz]

Just wondering if anybody can share some experiences with Electro-Harmonix small signal tubes. I've now gone through 2 spare 6922-EH in the past year and a half since owning my Seduction, and for what seems to be issues of durability: last year, one of the tubes developed a leak and went bad, as the getter turned white. Last night, I had no sound in one channel. I pulled off the tube shield and saw a dark tube. It was warm, so obviously the heater must have come on, but then failed. A failed heater? I thought those things were a little more durable! (FWIW, the two separate failures occurred across both sockets, not the same one, and the voltages are fine at the heater pins....)

In any case, I'm not impressed with these new-production tubes. Any recommendations for reasonably-priced 6DJ8/6922 NOS tubes I should check out?

[Doc B.]

Have you verified that the heater is open by removing the tube and measuring the resistance from pin 4 to pin 5? It should be quite low, just a few ohms. If it reads infinity it's open, but if you see a low resistance the tube may be OK and there may be something else going on.

[Dr. Toobz]

Didn't even think of that - a quick read shows a resistance of 4.xx ohms, so the heater is not open. Yet it doesn't light up. The tube does get hot quickly, though, much hotter than the other tube, after only a few seconds. I swapped sockets and the same thing happens - heat but no light or sound. Then, I tried a new 6922 and it works (and lights up) just fine. So, it would seem it's not a circuit issue, since it follows the tube. Problem solved with a new tube - good thing I have some spares.

Maybe something is shorting internally (in the tube, that is?) Needless to say, I won't be putting this sucker back into my Seduction. Interestingly, neither Seduction tube should have much life on it - less than 500 hours, anyway, especially since I listen to more CD's than LP's (which I tend to digitize to 48/24, clean up, and listen to through my iMac/DAC).

[Jim R.]

Angelo,

Yes, that is an internally shorted tube.  Make sure all your tube socket pins are making good contact.  I had this same problem with some el84s and the problem was an intermittent socket pin that when floating caused an internal meltdown and the same thing happened, tube got very hot, very quickly, yet there was no glow from the filament.

-- Jim

[Maxwell_E]

As far as new production preamp tubes go, I've had excellent luck with JJ's. I'm not sure if they make a 6922, but I've been more than happy with their 12AU7, 12AX7, and 12AT7 in my guitar amps. Much better lifespan than what you're reporting, I've got a couple that are 5 years old now.

[Jim R.]

Yes, JJ does make a 6922, and a halfway decent one at that.  Break-in is a bit longer than some, but all in all a good value tube.

The JJ kt-77 is one of the worst they make, but other than that most of their other tubes range from decent to superb.

I actually just dropped a pair of brand new JJ 2a3-40s in my Fis yesterday and I'm shoked at how good they are right out of the box.  So good in fact that I really have no need to try anything more expensive, and they easily outclass the shuguang treasure 2a3z tubes in these amps -- and that's saying something.  Of course we'll see as time goes on how they change, but as they are they're wonderful.

Oh, and they are built like battleships.

-- Jim