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Old 26th February 2014, 06:25 PM   #11
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Originally Posted by euro21 View Post
Why primarily IDH triodes?
Direct heating tube's tone -IMHO- is far better (26, 10Y/VT25, 801/VT62, 2A3...).
These are all ST tubes. :-)
But....globe version of these tubes even better.
All NOS ST DHT's are over $20 as are current production tubes like the 2a3.

I picked up 50 NOS 1626 for under $2 each a few months ago on eBay.
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Old 26th February 2014, 06:57 PM   #12
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New production Tung Sol 6l6G can be had for around $25.
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Old 26th February 2014, 07:14 PM   #13
TheGimp is offline TheGimp  United States
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1626 is specified as a class C tube, and the graphs don't look very linear.

Have you had a chance to try them, and if so how do they sound?

Last edited by TheGimp; 26th February 2014 at 07:18 PM.
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Old 26th February 2014, 07:43 PM   #14
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Originally Posted by TheGimp View Post
1626 is specified as a class C tube, and the graphs don't look very linear.

Have you had a chance to try them, and if so how do they sound?
It's a pleasant sounding tube and a big improvement over the chipamp in my office which it replaced. That being said, you won't mistake this tube amp for a well designed DHT amp. I copied the original darling by Danielak, a well documented design.
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Old 26th February 2014, 11:51 PM   #15
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I am familiar with the 1626, but didn't list it before since the mu is a little low for my needs.

On a completely different note... What does one mean by 'the graphs don't look very linear'? I know that 'linear' usually means the distortion spectrum falls so that 2nd, 3rd, 4th, etc. harmonics essentially look like a straight line. But, how does one see that from the datasheet?
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Old 27th February 2014, 08:45 AM   #16
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Originally Posted by needtubes View Post
But, how does one see that from the datasheet?
You can see in the Vg -> Va/Ia graph if the distance between the curves doesn't change much, if at higher current the curves are almost straight and they remain relatively parallel (they don't fan out much).

You can also look at the Va -> Vg/Ia curves : you should use the tube within the linear part of this curve.

You can take a look at a 300B as an example of linear device, and at, say, a 12AT7 for a less linear one.
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Old 27th February 2014, 11:57 AM   #17
TheGimp is offline TheGimp  United States
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Here is an extreme case of a triode with poor linearity. It was specifically designed to have remote cutoff characteristics by varying the grid turn spacing to make the grid turns less dense at the ends and more dense in the center.

The 6386 is a remote cutoff triode.

http://www.mif.pg.gda.pl/homepages/f...142/6/6386.pdf

It is possible to calculate the harmonic from measurements taken from the graph.
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Old 27th February 2014, 05:08 PM   #18
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Ah. That clears things up nicely. Thanks!
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