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 NEW  Matt presents bias and operation data for the 6V6 tube in SE operation - 6V6 Single-Ended (SE) Ultra Linear (UL) Bias Optimization.

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PostPosted: 30 May 2011, 20:05 
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Excellent driver. Worth it to be driven by the silver dragon!

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PostPosted: 29 Jun 2011, 07:48 
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I bring you sad tidings. A $1 bi-polar 100V 47uf cap went S/C on the heater of a $325 300BSE. This caused the bias to drop to zero volts and the expensive tube draw more "I" than it was designed for. I think the TJ Full Music Tube has gone to that big amp in the sky but until I get my hand on it I will never know.

The cap shorting took out $2 worth of 5W limiting Rs. I found the Rs O/C and thinking this the only issue the amp had replaced them with a higher wattage set. Powering up the amp with the failed cap caused a EH 300B "coke bottle" to glow. Now I'm no expert but I can't imagine this endowering the tube with super natural sonic qualities. The EHs sound great right now but until I have run them through my friend's tester the jury is out. My tester can't do 300Bs.

This is crazy because the 100V cap only had to handle 71V. I think a X2 rating is required where you are not using expensive parts. Mind you the parts for this amp cost thousands. But one cheap part has played the part of the grim reaper here.

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PostPosted: 29 Jun 2011, 23:30 
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Nooooooooooooo............. :bawling:

There is a saying in electronics that the most expensive part in a circuit will always fail to protect a 10¢ resistor. In this case the cheap part went south and took the expensive one with it for good measure. In the design business we call this "infant death syndrome". It's due to insufficient new part screening at the manufacturer.

Let us know when you find out about the TJ Full Music 300B. Sometimes, if the plate is not damaged, a DHT can stand a significant over current condition for limited periods of time; so long as the oxides are not boiled off the filament/cathode. If the Rs went open circuit fast enough, the tube may be all right.

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PostPosted: 30 Jun 2011, 07:17 
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Matt: To protect these very expensive and limited edition tubes, fuses in the plate cct. may have been a good idea. Most say you can "hear" a fuse. My greatest fears tell me the 300B has suffered a terminating hart attack. Qian said the right tube did not light. And yes it was the right tube that had the failed cap, I think it gone but hope I'm wrong. IDS may have struck here. Keep you informed.

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PostPosted: 30 Jun 2011, 16:44 
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To protect these very expensive and limited edition tubes, fuses in the plate cct. may have been a good idea. Most say you can "hear" a fuse. My greatest fears tell me the 300B has suffered a terminating hart attack. Qian said the right tube did not light. And yes it was the right tube that had the failed cap, I think it gone but hope I'm wrong. IDS may have struck here. Keep you informed.


It was probably not the bypass capacitor but the 300B itself . Sounds like you had a grid to filament short : a known fault with TJ 300B . Look down into the tube and you'll see there are filament hangers for tensioning . In comparison a Shuguang or EH 300B will have springs which hold the filaments perfectly vertically . With hangers , distortion in transit is more than likely the cause . I avoid Chinese tubes with this style of filament support : TJ 300B , Shuguang type 50 and also Shuguang 300B-S have this style of filament . I've used all three of these and had issues which manifested after a few days use with loud 'cracks' and blowing fuses . the TJ's did sound superb for the short time I had a working pair...

I would also avoid bipolar electrolytics for best sound , try a Panasonic ED paralleled with a polypropylene film cap

BDA


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PostPosted: 30 Jun 2011, 17:08 
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bda: Yes the thought went through my head that in the end it may have been a failed tube. After what you have just written I'm now convinced this was the case. The bypass caps I used were 100V 47uf biploars. Matt's design placed 71V across the cap. Well within it's specs. As I stated one went very short cct. The owner said the tube does not light. All of this points to tube meltdown.

Qian, the owner, will want to replace this tube which means buying another pair (AU$650). If it happed again he might be blaming me when, as you have said, may be a fault with the tube. I will inspect the tube. You are saying I will see the filament against the grid if this has happened?

What is the alternative to the TJ Full Music tubes? What sounds as good if not better? WEs? As it happens I just bought a pair of TJs. The same fate may plague me??!!??

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PostPosted: 30 Jun 2011, 20:36 
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Hi All, this reminds me why I use KT88s and KT120s. The bit about the 10 cent part being saved by the $100 one is certainly something I have seen. The sand resistor is always fine, the expensive rectifiers and regulators are toast. :hot: BTW I concur on not using bi-polar electrolytics. Good for crossovers where the values are huge but not anyplace else. I have long been suspicious of them and how they are made. It seems to me that just the concept is contrary to how electolytics are made and supposed to work. The polarization issue would seem problematic. Just some unsubstantiated ramblings of an old tube dude....

Good listening
Bruce

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PostPosted: 01 Jul 2011, 03:42 
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gofar99 wrote:
Hi All, this reminds me why I use KT88s and KT120s. The bit about the 10 cent part being saved by the $100 one is certainly something I have seen. The sand resistor is always fine, the expensive rectifiers and regulators are toast. :hot: BTW I concur on not using bi-polar electrolytics. Good for crossovers where the values are huge but not anyplace else. I have long been suspicious of them and how they are made. It seems to me that just the concept is contrary to how electolytics are made and supposed to work. The polarization issue would seem problematic. Just some unsubstantiated ramblings of an old tube dude....

Good listening
Bruce

I hear you brother. I replaced them with 100uf 400V. Yes over-kill but all I had. I don't think the 100uf will hurt anything.

Interesting observation, paying the Silver Dragon with the EH 300B Golds at normal volume was a bit dull. I just played it up real loud and it sounded sssssssooooooooooo much better. The amp grew balls and proclaimed itself king of the listening lougne. Can't wait for the wife to go out so I can do it again.

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PostPosted: 01 Jul 2011, 07:11 
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Joined: 18 Jun 2010, 12:46
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Location: Northern VA
Shuguang Treasure 300B are supposed to be as good as the TJ, or very close. I have not compared them side by side, just looking at the reviews.

I do know that the Shuguang Treasure 6CA7 sound better than NOS Mullard XF2 EL34 if that means anything to you. (In the Mullard 5-20 circuit)


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PostPosted: 01 Jul 2011, 09:52 
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rock4016 wrote:
Shuguang Treasure 300B are supposed to be as good as the TJ, or very close. I have not compared them side by side, just looking at the reviews.

I do know that the Shuguang Treasure 6CA7 sound better than NOS Mullard XF2 EL34 if that means anything to you. (In the Mullard 5-20 circuit)

I have taken a back-step and now feel strongly that the failed TJ 300BSE was due to a failed cap. Bruce's comments about bipolar electros and the fact that a failed tube may not even be able to to blow a cap (but again it is slightly possible)) would suggest a acap failure.

This pleases my over-weight-amp-building-body. Because I now owen a AU$650 pair of TJs. And as long as I can purchase some 47uf 100V reliable caps all the world is Rosie again.

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