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Old 9th February 2012, 09:32 PM   #11
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Originally Posted by the_manta View Post
Thanks for the link ! I hope these will last longer.

The failed tube is an Electro Harmonix (EH) 300B. The standard one, not the gold-grid or whatever one. I made a photo. It's one of the left pair. (The right ones with the carbon plates are some early production chinese.)
I looked up some pictures of the Sovtek 300B and the internals look exactly the same. Well, no suprise - they both came from the Reflector/New-Sensor plant in Saratov I guess.
The broken filament happened on my old Sovtek, but my new EH 300B Gold seems much better made, and sounds excellent.

What kind of heating do you use? I believe ac heat with big transformers can really punish the filament with high turn-ON current pulse, 3x higher than normal current.

Lastly, In your photo, the EH show date code 08 02 - made in year 2008! if you bought them in 2011, where have they been for 3 years?
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Old 10th February 2012, 11:51 PM   #12
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Originally Posted by Rod Coleman View Post
<snip>

What kind of heating do you use? I believe ac heat with big transformers can really punish the filament with high turn-ON current pulse, 3x higher than normal current.

<snip>
This is true to some extent in my experience, and DC filament supplies that are not designed to limit inrush current can also cause reliability problems with some 300B tubes. I recommend CCS heating by whatever means for dhts with 5V filaments and above.
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Old 11th February 2012, 08:58 AM   #13
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Hi Kevin,

It's true, raw rectified dc is just as bad for turn-ON overcurrents. It's also the worst-possible sounding heating method!

BTW, I was using 1998-vintage JJ 300B until lately. They were reliable and good-sounding for 11 years of use, must have been 5000 hours or even more. But I bought new EH 300B Gold when the getters of the old triodes began to get thin. After a year with the EHs, I find their sound to be better than the JJ, particularly in articulation. These are 2010-year production, and I rate the build quality to be very good - internal alignment and straightness, and finish is far better than the old Sovteks.

I recommend them.
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Old 11th February 2012, 10:31 AM   #14
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Originally Posted by JimW View Post
I have two mono blocks, and two stereo amps using 300B (that's 6 EH 300bs total), one of the stereo amps sees daily service, and I can honestly say I have not had an electrical failure. Four of these tubes have been in use since 2006. I have had two broken (kids involved) tubes, one EH and one JJ. I do occasionally rotate JJ's in and out of service, as they do sound a bit better, but the EH have been satisfactory for the most part (they are more microphonic than the JJ). Now I do run the tubes conservatively, perhaps that makes a difference, the hottest of the amps runs them at 28 watts, the monoblocks at 25 watts, and the remaining amp runs them at 20 watts, and I also have made sure the filament voltage doesn't exceed 5.1-2 volts. I do have a stereo 2a3 amp that has had the same tubes in for 8-9 years (EH), but this amp doesn't see a lot of action these days although I used it in my office for 9-10 hours a day for about 5 years. I do make it a point to periodically reseat the tubes, as I have had sockets lose contact, which can be a big deal if it happens to be the grid pin that makes poor or no contact.
Hummm... This supports my suspect that some tube shops buy rejected or low quaality tubes and sell it as good or at sensible prices.

The Manta´s defective tubes are Sovtek from 2008, its are not early production tubes, so seesm to be problematics/rejected tubes;

If someone had a better ideia please fell free to post.
Thanks
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Old 11th February 2012, 11:59 AM   #15
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Originally Posted by Rod Coleman View Post
Hi Kevin,

It's true, raw rectified dc is just as bad for turn-ON overcurrents. It's also the worst-possible sounding heating method!

BTW, I was using 1998-vintage JJ 300B until lately. They were reliable and good-sounding for 11 years of use, must have been 5000 hours or even more. But I bought new EH 300B Gold when the getters of the old triodes began to get thin. After a year with the EHs, I find their sound to be better than the JJ, particularly in articulation. These are 2010-year production, and I rate the build quality to be very good - internal alignment and straightness, and finish is far better than the old Sovteks.

I recommend them.
EH is a sovtek production tube. I think that is quite normal that a new EH sounds better than an 11 years old JJ, expecially if the JJ has 5000 hours!
I wolud compare the two tubes after using the EH for 11 year and 5000 hours.
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Old 11th February 2012, 01:14 PM   #16
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Originally Posted by francoiacc View Post
EH is a sovtek production tube. I think that is quite normal that a new EH sounds better than an 11 years old JJ, expecially if the JJ has 5000 hours!
I wolud compare the two tubes after using the EH for 11 year and 5000 hours.
Yes, naturally, this is true.

The EH still sounds really good, in an absolute sense.

I will try to remember to dig out the old JJs in the year 2023, if I am still alive and hearing properly - and I will compare the sound again, and write my report here!
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Old 11th February 2012, 02:33 PM   #17
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Yes, naturally, this is true.

The EH still sounds really good, in an absolute sense.

I will try to remember to dig out the old JJs in the year 2023, if I am still alive and hearing properly - and I will compare the sound again, and write my report here!
Click the image to open in full size.
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Old 11th February 2012, 02:57 PM   #18
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Originally Posted by Rod Coleman View Post
What kind of heating do you use? I believe ac heat with big transformers can really punish the filament with high turn-ON current pulse, 3x higher than normal current.

Lastly, In your photo, the EH show date code 08 02 - made in year 2008! if you bought them in 2011, where have they been for 3 years?
The tubes were bought several month before the chinese 300B's failed. They came from a large german supplier. It was a good deal and I (well, my Dad) was happy to have some spares. I think the supplier just bought a huge batch.

The amplifier is a commercial product from a german company. It's a Welter 300B SE. Heating is DC but no current limiting. I thinking about an upgrade.

Quote:
Originally Posted by Rod Coleman View Post
I will try to remember to dig out the old JJs in the year 2023, if I am still alive and hearing properly - and I will compare the sound again, and write my report here!
I'm looking forward to reading it here
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Old 11th February 2012, 10:47 PM   #19
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Originally Posted by francoiacc View Post
EH is a sovtek production tube. I think that is quite normal that a new EH sounds better than an 11 years old JJ, expecially if the JJ has 5000 hours!
I wolud compare the two tubes after using the EH for 11 year and 5000 hours.
I don't think so. For me the JJ300B is best 300B money can buy today and 5000 h are not a lot for a properly used 300B, it is almost like new. Not the cheapest but surely the most convenient, including the performance. As always one needs to ask for some serious selection or, at least, avoid buying from unknown sellers....

Last edited by 45; 11th February 2012 at 10:54 PM.
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Old 11th February 2012, 11:00 PM   #20
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Originally Posted by 45 View Post
I don't think so. For me the JJ300B is best 300B money can buy today and 5000 h are not a lot for a properly used 300B, it is almost like new. Not the cheapest but surely the most convenient, including the performance. As always one needs to ask for some serious selection or, at least, avoid buying from unknown sellers....
Manta bought from a large Germany shop, surely a respected vendor and had this bad tubes!!

I start suspecting noone test any tube, by lack of time, test equip and qualified personal.
Too bad, so rest us to buy at VTS, UPSCALE and others top money tube brokers...
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