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Old 20th January 2012, 02:17 PM   #11
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Here is the link. I knew I had it saved as one of my vacuum tube bookmarks. As a beginner in wanting to make a first amplifier, I think I have saved at least 100 links covering various problems from blue smoke to no sound from diyaudio.com alone (which has probably kept (or scared) me from starting my projects for the previous six months ).

what just happened? Plate glowing

I hope that this one applies and best of luck.
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Old 20th January 2012, 04:42 PM   #12
kevinkr is offline kevinkr  United States
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There are a number of inexpensive 300B that just do not work at 400V, and exhibit exactly the kind of behavior you describe. I've found JJ, and EH types to be pretty reliable.
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Old 21st January 2012, 07:19 AM   #13
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So, the good news is that we have music again. The tubes look fine, I had them tested with tube tester and with an amp in a shop. If you are in Tokyo visit Hino Audio, They don't speak a word of english, but they are so nice, that you manage to find your way.

Anyway, I changed the mosfet, but I am not sure that were the cause of the problem. Now I have a lower B+ and a more conservative bias and everything looks fine.

The tubes are Golden Dragon 4-300BC, should be kind of good. I had been using them at 390 V 75mA for a couple of year. Maybe mat B+/bias was really exaggerated.

Is it possible that the tubes kind of recovered during the time I did not use them ?

Thanks,

D.
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Old 21st January 2012, 02:04 PM   #14
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Quote:
Originally Posted by Nikon1975 View Post
So, the good news is that we have music again. The tubes look fine, I had them tested with tube tester and with an amp in a shop. If you are in Tokyo visit Hino Audio, They don't speak a word of english, but they are so nice, that you manage to find your way.

Anyway, I changed the mosfet, but I am not sure that were the cause of the problem. Now I have a lower B+ and a more conservative bias and everything looks fine.

The tubes are Golden Dragon 4-300BC, should be kind of good. I had been using them at 390 V 75mA for a couple of year. Maybe mat B+/bias was really exaggerated.

Is it possible that the tubes kind of recovered during the time I did not use them ?

Thanks,

D.
Well, that is good news that nothing really went South. Did you manage to try the tubes in the amp you had them in previously? You might be able to tell sonically, or visually (though it is very subjective).

I am not sure about tubes recovering -- the only recovery they can do is cool down (the inards can't do much of that very efficiently in a vacuum either).

Keep an eye open now and then and check the bias after a while in case of drifting form things like the tubes themselves or drift in any of the electrolytic capacitors.

Take a picture of the amp, I am curious to what it looks like.
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Old 21st January 2012, 06:29 PM   #15
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Looks like the lower B+ is the answer.
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Old 21st January 2012, 07:45 PM   #16
kevinkr is offline kevinkr  United States
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Originally Posted by toprepairman View Post
Looks like the lower B+ is the answer.
I agree, and I have had this problem with older versions of the Shuguang 300B and Valve Arts tubes, but rather hoped that they had fixed the issue by now. (Grid not extended sufficiently beyond the plate structure to allow cut off at plate voltages much above 350V or so. Once you can't actually cut off plate current you have lost control of the tube.)
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Old 22nd January 2012, 12:08 PM   #17
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You always have to see things in prospective: yesterday I was crying for the potential loss of my 200 $ tubes.

Today, just in front of my eyes, my two years old son pushed one of my expensive speaker, that felt on a 52 inches LCD screen. I managed to catch the speaker before the floor, but not before the screen

Results: scratches on the speakers and LCD in pieces.

AAAAAAHHHHHHH !!!!!

Sorry, I needed to vent.

D.
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Old 22nd January 2012, 12:09 PM   #18
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Maybe is a sign, that I need heavier speakers, and a projector.

D.
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Old 22nd January 2012, 01:50 PM   #19
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Originally Posted by Nikon1975 View Post
You always have to see things in prospective: yesterday I was crying for the potential loss of my 200 $ tubes.

Today, just in front of my eyes, my two years old son pushed one of my expensive speaker, that felt on a 52 inches LCD screen. I managed to catch the speaker before the floor, but not before the screen

Results: scratches on the speakers and LCD in pieces.

AAAAAAHHHHHHH !!!!!

Sorry, I needed to vent.

D.
Not to worry. My son at an early age smashed my laptop computer accidentally. So I went out and got a new one. It was a great upgrade.

So you see, in your situation, an upgrade to an 80 inch is now in the cards, a set of 4 larger speakers (one pair to use and one pair for backup). This means another amplifier also for the backup speakers, new inputs, and a new computer (so you can put your thoughts on diyaudio)..
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