how about them... - Joelt - Tube DIY Asylum

how about them...

Posted by Joelt (A) on June 15, 2005 at 06:35:58

In Reply to: How about ALL the numbers... posted by Triode_Kingdom on June 14, 2005 at 20:02:35:

>>Although the 12AX7 does indeed have a few sweet spots, you have to search for them. It's clearly inferior to its octal predecessor under most conditions.>>

Hi TK,

I'm not quite sure how you are looking at this chart, and then deriving the idea that the 12AX7 inferior "under most conditions".

If you average the output voltage and distortion of the 250V operating point for each tube, with the same signal voltage of 0.1V you get:

12AX7 6.34V 0.3%
6SL7 4.8V 0.5%

In order to do a one-to-one comparison we lower the 12AX7's output and distortion by the ratio of the difference between its Eo and the 6SL7.

4.8/6.34=0.757
0.757*0.3=0.23%

So, at an output of 4.8V, the 12AX7 will have an average of 0.23% distortion. Quite clearly this is lower than the 6SL7's 0.5% average. By half in fact.

If you raise the input voltage of each tube until just under grid current flows, as the chart shows, then the 6SL7 overtakes the 12AX7 in performance. It can do a larger output swing, clearly. So, as both Cheap-Jack and I said, it's all about the circuit, choosing the right operating point, and choosing the right tube for the job at hand.

Now, I know you think that Sylvania cherry-picked some operating points you're calling "sweet spots" - but maybe you could explain to me what a "sweet spot" is, other than simply operating the tube within its linear region. Clearly the tube doesn't have some magical region that can only be found by experimentation?

Joel

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Follow Ups Full Thread

Topic - 6SJ7 conversion to 12AX7 - stevenelaw@sbcglobal.net 21:42:07 06/13/05 (24)

Re: 6SJ7 conversion to 12AX7 - Triode_Kingdom 22:32:56 06/13/05 (23)

Link? To sleeve pricing? (pic) - LineArrayNut 15:15:16 06/14/05 (0)

Re: 6SJ7 conversion to 12AX7 - fatbottle 07:46:11 06/14/05 (0)

"inferior"? In what sense? - Joelt 05:18:30 06/14/05 (18)

Sonically - Triode_Kingdom 08:19:19 06/14/05 (16)

Who cares! - cheap-Jack 11:14:58 06/14/05 (14)

the PAS is a good example - Homer Jay 16:00:00 06/14/05 (0)

Lets consider that this is a DIY forum - Russ57 12:32:54 06/14/05 (12)

Re: Lets consider that this is a DIY forum - Joelt 15:03:00 06/14/05 (1)

Yes, you've said it. (nt) - cheap-Jack 18:48:34 06/14/05 (0)

You make your point, but... - cheap-Jack 13:42:16 06/14/05 (1)

So, why not be constructive instead of setting up flames! - Homer Jay 16:02:10 06/14/05 (0)

But even more important... - Triode_Kingdom 13:20:52 06/14/05 (7)

how about some numbers - Joelt 14:56:05 06/14/05 (6)

How about ALL the numbers... - Triode_Kingdom 20:02:35 06/14/05 (4)

how about them... - Joelt 06:35:58 06/15/05 (3)

Not real world - Triode_Kingdom 08:18:47 06/15/05 (2)

Welcome to the 'real world". - cheap-Jack 12:29:07 06/15/05 (0)

you're changing the parameters of your argument - Joelt 09:21:42 06/15/05 (0)

You're just confusing the opinions with facts Joel. - kyle 15:13:51 06/14/05 (0)

Re: Sonically - Joelt 09:12:34 06/14/05 (0)

Agreed. All depends on design. (nt) - cheap-Jack 07:33:42 06/14/05 (0)

Re: 6SJ7 conversion to 12AX7 - stevenelaw@sbcglobal.net 23:06:00 06/13/05 (1)

Re: 6SJ7 conversion to 12AX7 - Triode_Kingdom 08:12:10 06/14/05 (0)

Follow Ups

how about them... - Joelt 06:35:58 06/15/05 (3)

Not real world - Triode_Kingdom 08:18:47 06/15/05 (2)

Welcome to the 'real world". - cheap-Jack 12:29:07 06/15/05 (0)

you're changing the parameters of your argument - Joelt 09:21:42 06/15/05 (0)

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