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Old 28th January 2013, 06:29 AM   #11
tcqanh is offline tcqanh  Viet Nam
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Quote:
Originally Posted by Vinylsavor View Post
Hi!

I have used the 6N7 a lot as driver tube in two stage amps. Works nicely

Thomas
Does anyone use 6F8G for driver tube ? These tube have the same data to 6N7, 6SN7, 6J5, 6P5 ...
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Old 28th January 2013, 01:04 PM   #12
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Hi

Quote:
Originally Posted by tcqanh View Post
These tube have the same data to 6N7, 6SN7, 6J5, 6P5 ...
6N7 and 6SN7 do not have the same data! They are quite different

Thomas
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Old 1st February 2013, 06:36 AM   #13
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Hi!

A nice tube which is electrically equivalent to the 6N7 is the 6A6:

VinylSavor: Tube of the Month: The 6A6

Best regards

Thomas
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Old 1st February 2013, 04:03 PM   #14
TheGimp is offline TheGimp  United States
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I tried 6AC7s last night out of a dozen used tubes, two looked like new and came in around 0.1%thd at 102Vp-p. Nice decay in harmonics below -100dB by the 4th. Most of the tubes came in between 0.15 and 0.24%thd, with a couple worse than 0.3% and nasty harmonics slowly decaying.

I think I have a half dozen 6N7s so I'll give them a try next. A couple are in boxes, but may not be NOS as they came from a TV repair shop that put used tubes back in boxes and forgot to throw them out.
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Old 2nd February 2013, 05:34 AM   #15
TheGimp is offline TheGimp  United States
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Only two 6N7s, and a 7 6J5 plus two 6J5-GTs.

The 6N7s were great at low current but above 6mA they went wonkie. High order harmonics rapidly increased.

6Y7 was a disappointment as distortion went up rapidly above 3mA. Not much drive there even with the plates in parallel.

6J5GT looked promising although a bit high on second harmonic.
Plots are:

6N7 at 6.5mA
6N7 at 6mA
6N7 at 7mA

6Y7 at 2mA

6J5GT at 5mA
Attached Images
File Type: jpg 6N7-6-5ma.JPG (91.5 KB, 480 views)
File Type: jpg 6N7-6ma.JPG (88.6 KB, 476 views)
File Type: jpg 6N7-7ma.JPG (93.9 KB, 376 views)
File Type: jpg 6Y7Parallel.JPG (87.1 KB, 366 views)
File Type: jpg 6J5GT.JPG (81.4 KB, 358 views)
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Old 2nd February 2013, 07:31 AM   #16
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Hi!

Judging the distortion results by the current alone is meaningless. What was the test circuit and other op point parameters? Could well be that the 6N7 was driven into grid current at the higher current op points. Then higher distortion is expected. If other parameters get adjusted the results might well be different.

Best regards

Thomas
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Old 2nd February 2013, 10:45 PM   #17
TheGimp is offline TheGimp  United States
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Good point. I did verify that they weren't approaching clipping by increasing the output to 120Vp-p while watching the waveform.

All were at Va ~= 200V.

I just re-measured one 6N7 and got this:

Vgk = 2.77V
Ik = 7.48mA
Va = 199.8
Vi = 2.82Vp-p
Vo = 103Vp-p

Clipping occurs on the positive peak first just above 148Vp-p
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Old 2nd February 2013, 11:29 PM   #18
TheGimp is offline TheGimp  United States
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Oops. That is with two triodes in parallel.

Clipping is stilla bove 148Vp-p

Single triode:
Vgk = -1.24V
Ik = 6.55mA
Va = 198.2v
Vi=2.92Vp-p
Vo = 102Vp-p

So yes, it is going into A2 operation even though I can't see any effect on the waveform (no clipping any way).
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Old 3rd February 2013, 04:41 AM   #19
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Hi!

I usually run the 6A6 at about 5-6mA grid bias -5 to -6V
B+ 250-300V

Best regards

Thomas
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Old 10th May 2013, 01:55 AM   #20
tcqanh is offline tcqanh  Viet Nam
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I'm trying to run Vak 335V, 45mA for Kenrad bi-plate 6B4G. Is it safe for those tubes ?
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