JJ ECC81/12AT7 Longevity - diyAudio
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Old 22nd March 2010, 04:33 PM   #1
rknize is offline rknize  United States
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Default JJ ECC81/12AT7 Longevity

I have quite a few of these tubes that I purchased in the last year or two...probably 8 in all. I bought a small batch of them at once to try and find two that had reasonably matches sections for use in the VTA-70 board. So three have been in service there and another has been in my Simple SE for the past year or so. They maybe have a few hundred hours on them at the most.

While chasing some strange behavior in another amp, I've recently noticed that the tubes that are in service are getting pretty worn given the relatively low hours. I verified this in a tube tester (Eico 666). While tube testers are not definitive, I trust poor results when comparing the reading with known-good tubes that test strong. The used tubes all test about 60-80%.

Anyone else observe this? There was someone on AA making a similar complaint. At the very least, I will be stocking up on JAN tubes and won't be buying any more of these JJs.
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Old 22nd March 2010, 05:23 PM   #2
SY is offline SY  United States
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FWIW, I've had the same pair in my power amp for two years now with no noticeable deterioration.
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Old 22nd March 2010, 06:05 PM   #3
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The RLD?
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Old 22nd March 2010, 06:42 PM   #4
SY is offline SY  United States
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Yep.
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Old 22nd March 2010, 06:45 PM   #5
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I don't have a tube tester or any other test equipment besides DVM's.
Recently, I took the stock OEM (Chinese) tubes from my Primaluna 3 preamp to a friend with a reliable tube tester, just to see what shape they were in after around 2k hours. They measured uniformly low. But the preamp sounds wonderful and always has. Just for the hell of it, I subsequently replaced the Chinese tubes with some Russian products, and the unit still sounds good.
My point is, I trust my ears, and the music tells me everything I want to know about the condition of the tubes.
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Old 22nd March 2010, 06:47 PM   #6
rknize is offline rknize  United States
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Quote:
FWIW, I've had the same pair in my power amp for two years now with no noticeable deterioration.
I was able to get these weaker tubes working in a similar circuit to yours by modifying some of the resistor values. What I ended up with was actually closer to what you have for plate loads in the RLD and in that case they did function.

Anyway, my main concern is longevity. I can get Philips JAN tubes for the same price or less as the JJ.
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Old 22nd March 2010, 06:50 PM   #7
rknize is offline rknize  United States
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Quote:
Originally Posted by neonthecat View Post
My point is, I trust my ears, and the music tells me everything I want to know about the condition of the tubes.
I agree...it totally depends on the circuit. The tube from the SSE tests marginal, but it sounds perfectly fine. The CCS on the plates probably keeps their gain up, though I will likely take a closer look at that at some point.
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Old 23rd March 2010, 08:38 AM   #8
OneyedK is offline OneyedK  Belgium
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Quote:
Originally Posted by rknize View Post
While chasing some strange behavior in another amp, I've recently noticed that the tubes that are in service are getting pretty worn given the relatively low hours.
Please measure the heater voltage.
(at startup and when the amp is running for an hour or so)

I noticed the same problem in several (modern) guitar amps, and every time the heater voltage was on the high side, especially with unregulated DC voltage.
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Old 23rd March 2010, 02:26 PM   #9
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I'll take a look at that. I seem to recall the SSE was spot-on, but I will double-check. Lowering the heater a bit for the small signal tubes is probably not a bad idea, though.
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Old 23rd March 2010, 04:10 PM   #10
kevinkr is offline kevinkr  United States
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I've noticed in past retubes of former client's gear that the JJ 12AX7A sounded great when new, but deteriorated fairly quickly, and noticeably so. (After a couple of thousand hours of use.)
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