Q: lifespan of JJ ECC99 tubes

[Irakli]

Hi All,

I have two monoblocks of Lynn's Amity amplifier which use JJ ECC99 dual triodes to drive PP 2A3s.

When I plug brand new ECC99 tubes, the amplifier sounds fantastic. However, after about a year or so of normal use sound changes and becomes "grainy" (meaning it is distorted). $30 spent on new tubes brings things back to normal. I have replaced driver tubes each year for three years now.

Measured parameters for new JJ ECC99 tubes are according to specs. However, when I measure same tubes after several months the same parameters are off significantly.

Here is my question: is it normal for JJ ECC99 to have such a short lifespan?

please share your experience with this tube. Thanks.

[tinitus]

allow me a possibly stupid thought, but how about adjustments, and how much ?
but maybe they do live a hard life as driver tubes
would be interesting to know more

[Irakli]

Originally Posted by tinitus

maybe they do live a hard life as driver tubes

Nothing extraordinary.
Ua=145V Ia=18-20mA (per section).

Here is the schematics:
http://www.nutshellhifi.com/IT-Triode-Amp.gif

BTW, power tubes are three years old and going strong (EH 2A3s).

[lechuck]

I just started using the ECC99 two weeks ago so I am unable to answer your question (yet). I am using the ECC99 as CF's to drive the output stage of my dc coupled PP amp, so far they are performing really well. I will let you know if I find them degrading over the next couple of months.

I don't see a specific reason for using the ECC99 in your application. The main advantage of the ECC99 is it's current handeling capability. In my situation I chose them because I needed a twin triode capable of delivering enough current to drive the screen grids of my output stage. In your situation I expect a 'lower-current' twin triode could also do the job.

Have you tried to replace the ECC99 with a different twin triode? The ECC82 immediatly comes to mind because the pinout is the same. Personally I would try if a 6CG7 (noval version of the 6CG7 with a mu of 20) works for you.

[Doz]

Doesn't an ECC82 have different split heaters for 6.3/12.6 operation with pin 9?

[lechuck]

Originally Posted by Doz

Doesn't an ECC82 have different split heaters for 6.3/12.6 operation with pin 9?

It sure does, so does the ECC99.

[JimW]

I think the grainy sound comes from the tubes losing their section to section matching. I had to go through several to find a pair that matched well. I am using them in 2a3 amitys as well. As I am sure you know, the drive requirements are such you need a pretty ballsy tube. I use ecc99 as a directly coupled voltage amp/phase splitter in a pp el84 amp, and they have worked very well for quite a long time.

[pieter t]

Originally Posted by lechuck

Have you tried to replace the ECC99 with a different twin triode? The ECC82 immediatly comes to mind because the pinout is the same. Personally I would try if a 6CG7 (noval version of the 6CG7 with a mu of 20) works for you.

This is not a good alternative.
The amplifier is interstage transformer coupled, and hence the Rp of the driver tube is something to consider.
The ECC82 (or 6CG7, or 6SN7) have plate resistances (7k or higher) which does not make them a good choice for this application; it would require transformers with very high primary inductances, requiring many turns which leads to high winding capacities, in other words a no-go thing.
When the ECC99 is not reliable for life endureance, better try a 5687, E182CC or 6H30.

[Irakli]

Originally Posted by JimW

I think the grainy sound comes from the tubes losing their section to section matching.

I totally agree with you. Another remote possibility is that the driver stage starts to oscillate. I need to check for that too.

[Dinkers]

Hi, I removed the lamp and JJ ECC99 JJ KT88 from the amplifier 828 I used ECC82 and EL34 tubes, and is much better. JJ is a Slovak company / before Tesla / and their tubes are not good. Greetings Dinkers