Help. X-Cans tubes need replacing after 100 hours

[olsonr]

I have a modified X-Cans V1 that only gives about 100 hours before the tubes, JJ E88CCs, sound mushy and indistinct. Replacing the tubes restores the sound to normal. The mods include removal (jumping) C103, Panasonic PP for most of the signal caps (C109 is a 10uF Cornell-Dubillier PP, 105 deg. C Nichicon electrolytics with Panasonic stacked film in parallel for the decoupling caps, NPO ceramic capacitors, National Semiconductor LM4562 op-amps, and a 30VA 12V wall wart saved from a burglar alarm. I have also included a series resistor so that the filament voltage of the output tubes can be set to the 6.3 V nominal value. I can give more details if needed. The tube voltages all look normal, 0V at cathode, about .2V on grid (I assume that this is the output offset of the 4562) and 29.6V at the plate. All voltages taken with the amp disassembled and disconnected from the rest of the system. A peak reading voltage meter indicated about .3 V accross a 333 ohm resistor at my normal listening level. Headphones are Sennheiser HD650 with a 20 ft. Cardas cable.

Thank you in advance for any help anyone can give on why my tube life is so short.

[PinkFloyd]

Are you saying that you fit a brand new pair of valves and then, after 100 hours, they sound like shit so you replace them with another pair and then, 100 hours later, they also sound like crap?

[olsonr]

Yes. I replaced tubes on Feb. 10 after a previous set crapped out, and again last night. All of the short lived tubes have been JJs, so this time I used a pair of Sovteks that I had on hand.
I'm hoping that I may have just gotten a bad batch of tubes.

I originally thought that excessive filament voltage was the culprit. The filaments had about 7.2 V before I installed the series resistor. They are now very close to 6.3V.

[PinkFloyd]

Mar 30, 2011 22:01:31 GMT olsonr said:

Yes. I replaced tubes on Feb. 10 after a previous set crapped out, and again last night. All of the short lived tubes have been JJs, so this time I used a pair of Sovteks that I had on hand.
I'm hoping that I may have just gotten a bad batch of tubes.

I originally thought that excessive filament voltage was the culprit. The filaments had about 7.2 V before I installed the series resistor. They are now very close to 6.3V.

I would definitely go with the "bad valve" scenario for starters.... keep an eye on the sovteks and see how they go. Were the JJ's brand new or were they sold as "test ok" types? Could be that you bought a few "pulls" from used equipment that were already on their way out.

Do you have any way of checking the transconductance of the valves? That is a good way to establish that they are definitely knackered, I don't think your amp is destroying them prematurely!

Mike.

[PinkFloyd]

By the way... current production valves like JJ's aren't too hot.... if you are going to go Russian then go down the vintage 6N23P-EB route, they are built like tanks and have a very long lifespan.

[olsonr]

The JJs were new, purchased from Triode Electronics in Chicago.

I'm wondering if excessive grid current may have killed the tubes. The X-Cans don't have any negative bias on the grid as far as I can tell, so the grids will draw some current.

I'll keep an eye on the Sovteks, but I want to get a handle on the problem before I start using vintage tubes. I do not have a way of measuring transconductance, but a local high end dealer will test the tubes for me if they have a tester. I'll check.

Thank you.

[olsonr]

After a little more investigation online it looks likely that the JJ tubes are at fault. The poor reliability of the JJ is addressed on Tube Asylum
www.audioasylum.com/audio/tubes/messages/22/228448.html
and
www.jacmusic.com/tesla/tesla-jj.html
with the latter reporting emission dropping at 5% per HOUR!

I've ordered som Electro Harmonix tubes, which seem to be a favorite among current production 6922s. I suspect that this will solve my problem.

Thank you once again for your help.

[olsonr]

I see that this post has been read quite a few times in the last year, so an update is in order.

The Electro-Harmonix 6922s needed replacement after about 11 months. At least that is when I finally noticed that the sound had deteriorated. I typically listen to about one CD each night, and I allow the amp to warm up for 30-60 minutes before I start listening. Considering a few other factors - nights when I don't listen, nights that I leave the amp on by accident, etc. I figure that my usage amounts to 500 hours "ON", with about half of that actually playing music.

I don't know if it is "ON" time or playing time that chews up the tubes. It looks like the tubes see a load of 47 ohms in series with the impedance of the headphones, 300 ohms for my Sennheisers. This seems like a pretty tough load to me.

[XTRProf]

Hi there,

Thanks for your post. I'm going to stay clear of the Tesla JJ tubes. Btw, do you happen to have tested (sound wise) your X-Can with new generation Mullards? There were some favourable comments on those compared with the NOS Mullards. I'm interested to try some and I just recently bought a MF V2 HA.

Also, is the sound of the EH 6922 good to you? Any microphony when the chassis is tapped? My US Philips Jan 6922 sang like the winner of the American Idol show when tapped. Heh, heh, heh ................

[elysion]

The newer tubes (JJ, Electroharmonix etc.) are IMO crap. If you have problems with them, then I'd suggest you that you GO the vintage route. "Vintage" doesn't means "used" or "bad", I mean you should go for good NOS tubes from a reliable source.

Luckily, you don't have to search further. Write a PM to Mike ("Pink Floyd") and ask him which tubes he is selling currently. He has a lot of NOS tubes in stock, all in top-notch condition and, of course, also carefully tested and matched.

I really can recommend Mike as source for good NOS tubes. You won't regret it.

I'm also sure that Mike and all others on the forum will help you to ensure that it is only a tube related problem and not something else.

I've bought five pairs of Russian tubes from him last year and I'm really happy. I use them in my X-Can V2 and V3. Because he has matched the tubes so carefully, I have much less problems now. Before that (with unmatched tubes), I've had some problems with a slight channel imbalance on the V3.

I have just one Electroharmonix 6922 tube here and, frankly, I was very disappointed with this tube. It was new and was delivered with my Project Sunrise headphones amp (the amp is great BTW). I've replaced that tube with a Philips E88CC SQ (Special Quality) tube from the 60's. These are IMO also great tubes, but they are very rare and the few I have can't be matched anymore. That's why I use it in the Project Sunrise amp (it needs only one tube).

[olsonr]

I have not tried the Mullards, but I'll order a pair if they are not too expensive.

The Electro-Harmonix tubes sound fine to me. Good frequency extension, good articulation of voices. I have no complaint. I tapped the enclosure of my X-Cans last night and there was no trace of microphony from the month-old EHs.

I'm happy with the EH 6922s. Tube life is (barely) acceptable, they sound fine, and they are not expensive.

At this point I am very reluctant to use expensive tubes in this amp.

[Deleted]

People like SandyK have lived/worked with glass bottles a considerable part of their (in those days) young lives.
With the grade of technology of those days I might add around the top quality of that industry.
It's no surprise SandyK is not that fond of those amplification devices.
They 'degrade' from the first day they come in service (well some increase in certain aspects first).
How LONG they keep functioning within 'parameters' differs from tube to tube and even from tube half to tube half.

Not so with semiconductors...

I have an EH6922 (came with a G2) and several 'old' tubes (no NOS all 'pulled') and it's needless to say on technical grounds (bandwidth, hiss, gain, distortion) the EH6922 is the best of the bunch and is not microphonic at all.
I have only 3 tubes that are microphonic and these all have other technical issues as well.
Also have a new JJ ECC83S (returned the first one I got as one half didn't even work) and it's one of the worst tubes in my posession.
It was sold as 'low noise' but has higher noise than my old telefunken and Philips ECC83.

I would say Mikes NOS Russion tubes are the safest bet for good performance AND longevity.

[XTRProf]

Apr 21, 2012 17:08:00 GMT @solderdude said:

I would say Mikes NOS Russion tubes are the safest bet for good performance AND longevity.

Sounds good too!

Can we sing Rasputin again?

[olsonr]

I just installed a pair of 6N23P-EBs that I ordered from Mike and they sound terrific, much better than either the JJ or Electro-Harmonix in my opinion. Obviously, I cannot speak to their longevity at this point, but I'll post an update if anything noteworthy happens. Until then I guess that you can assume that no news is good news. Thanks again.

[PinkFloyd]

May 12, 2012 18:57:15 GMT olsonr said:

I just installed a pair of 6N23P-EBs that I ordered from Mike and they sound terrific, much better than either the JJ or Electro-Harmonix in my opinion. Obviously, I cannot speak to their longevity at this point, but I'll post an update if anything noteworthy happens. Until then I guess that you can assume that no news is good news. Thanks again.

Hi Rich, Longevity is superb with the 6N23P-EB... they are the "extended life", double getter support, built like tanks!

Glad you like them.

Mike.