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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: 15 Jun 2013, 22:20 
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Hi, The 6N1P ought to be fine. The 6N23P has a bit less dissipation and might not last as depending on the actual B+ across the tube (B+ minus loss in the trannies and minus the cathode voltage) is such that the 6DJ8 is running fairly close to its ratings. They survive well, but with a slightly lower dissipation on the 6N23P it might not. 6N1P is virtually identical in ratings to the 6DJ8 and I would expect it to last a long time as well. With minimum degradation of the output you could reduce the cathode current and try the 6N23P. I find that the available output now is considerably in excess of what is needed for any of my phones.

Good listening
Bruce

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PostPosted: 16 Jun 2013, 03:25 
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Just to make things more confusing. I measured the DC resistance from pins 4/5/9. 4/5 have, (cold), app. 2.4-ohms, and 4/9 or 5/9 have 1.2-ohms. This suggests 9 is connected to heaters. (which brings to mind all sorts of direction since 5 ts at GND, and, low and high supplies are both earthed at R/C filter (pre-earth) which means heater #5 is out of cir. giving #4 all 6V's, etc etc ) At this point i am thinking it may be some type of preheating built into the new E88CC's. One tube evens out after 15 seconds or so and the other up to one min. during while a rush can be heard, softly but there, and when evened, out dead silence. (still blows me away. Thanks again Bruce ). Having slept on it i am taking Matt's suggestion and enjoying the music. But thinking on it and still questions. :D


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PostPosted: 16 Jun 2013, 09:00 
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Hi, In 6DJ8 tube the heater is between pins 4 to 5. Pin 9 is an internal shield and should be grounded. I believe you are thinking this tube is like the 12AX7 family with has pin 9 being the center tap of the heaters. In them the voltage between pins 4 and 5 should be 12. If you use pin 9 in them you can connect pins 4 and 5 together. The the 12AX7 family of tubes will run on 6 volts with the voltage applied between pins 4 (tied to 5) and 9. The 6DJ8 does not have that option.

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Bruce

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PostPosted: 16 Jun 2013, 09:43 
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I have looked at the 12a_7 family as well as 6DJ8/ECC88/E88CC and know of what you speek but the impedance measurements i get using a Fluke 77 VOM connected directly to the tube when not in cir. This is what leads me to believe it is some type of deliberate pre-heater from the manufacture. I thought at first also there should be NO connection between 4/5 and 9 but there is. The description of what is happening in the tubes with the heaters is visual and repeats every time.


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PostPosted: 16 Jun 2013, 09:57 
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12AX7:
Image

ECC88/6922/6DJ8:
Image

6N1P:
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PostPosted: 16 Jun 2013, 11:43 
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Hi, If there is a connection between pins 4 or 5 and 9 then the tube is defective or perhaps your measuring techniques is flawed. There are tubes with controlled warm up times but the 6DJ8 is not one of them. Most of those tube are one designed for operation directly (in series) across the AC mains. They often have unusual filament ratings like 13, 21, 35, 50 etc.

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Bruce

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PostPosted: 16 Jun 2013, 11:56 
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Hi, There was a request for an earlier version of the circuit using the 6J6 tubes. So here it is.

Good listening
Bruce
Attachment:
Hear Watt July 25, 2011.jpg


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PostPosted: 16 Jun 2013, 12:56 
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OK. i am taking them both back to my supplier and going to let him see for himself. I have measured the 4/5 and 4/9 and 5/9 dc resistances over and over,, and they are constant, and 9 is connected to 4/5 (smak-dab in the middle of them) so very strange. May very well be a defect as it would (one would think) be mentioned somewhere in the specs. The brightness of the 4/9 heater is what worries me as it is very bright until it settles down so definitely will be reducing the life.
Thank you all for your input guys, I will keep you informed.
And thanks Bruce for the 6j6 sch. I see the progression.


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PostPosted: 16 Jun 2013, 19:38 
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laurie54 wrote:
OK. i am taking them both back to my supplier...
Not a bad idea. I've had problems with new 6DJ8s before and didn't even know it. See here. I am interested in hearing what the vendor has to say.

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PostPosted: 18 Jun 2013, 11:58 
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OK back from supplier. WE plugged into tube tester. No 88's in manual but 6922 has 2 listings so used them. One says everything is fine, the other gives no reading at all. No explanation of what the "SELECTOR' sw is selecting and no info in book. So i bring home, plug in, and after very bright heater looks normal enjoy the music still non the wiser.


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