John Curl's Blowtorch preamplifier part II - Page 1655 - diyAudio
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Old 13th October 2011, 04:08 PM   #16541
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Good to see you back, Thorsten. Just in time! Now we have some new material to work with.
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Old 13th October 2011, 04:24 PM   #16542
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Quote:
Originally Posted by ThorstenL View Post
I can tell you how I did it, if that helps?

E88CC parallel cascoded, run at loads of current. Probably around 2nV|/Hz A Weighted... The WE 437A also comes clsoe to those noise figures, arguably tubes need to be selected.

If we can use more exotic tubes we can do better. The E810F run at zero bias and around 40V Anode voltage (cascoded) gives similar trasconductance and noise as a 2SK170...
Hi Thorsten, I'm glad to see you back.

You also did JSK147 cascoded by 5842 tube on your Toccata MKII MC front-head.

How about 2SK170 cascoded by E88CC/6922, or E810F/ 7788 triode connected, or C3g triode connected?
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Old 13th October 2011, 04:26 PM   #16543
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Quote:
Originally Posted by ThorstenL View Post
E810F/7788 triode wired
Do you have the data for E810F/7788 and/or C3g in triode mode?
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Old 13th October 2011, 04:38 PM   #16544
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Quote:
Originally Posted by Joshua_G View Post
Do you have the data for E810F/7788 and/or C3g in triode mode?
"Search" is your friend.

7788 Triode Curves
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Old 13th October 2011, 04:57 PM   #16545
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Quote:
Originally Posted by Joshua_G View Post
Hi Thorsten, I'm glad to see you back.

You also did JSK147 cascoded by 5842 tube on your Toccata MKII MC front-head.

How about 2SK170 cascoded by E88CC/6922, or E810F/ 7788 triode connected, or C3g triode connected?
Some RF jFETs, like CP650 (US part) or KP903A (similar russian part) are much better than 2SK170
For the KP903A the datasheet says
typical 0,7 nV/sqHz
Idss 300... 500mA
transcondactance 85 mA/V
Ciss = 18pF
dissipated power 6W
I have used these KP903A successfully both as an input transistor (cascoded) in preamp, and as an output transistors (8 matched pcs in parallel) in SE power amp.
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Old 13th October 2011, 05:08 PM   #16546
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Hi,

Quote:
Originally Posted by Joshua_G View Post
How about 2SK170 cascoded by E88CC/6922, or E810F/ 7788 triode connected, or C3g triode connected?
Yes, can all be done. If using the simple direct cascode it is necessary to watch the current of the J-Fet (means selection) so it gets enough voltage to work. It's basically all in the various datasheets.

Quote:
Originally Posted by Joshua_G View Post
Do you have the data for E810F/7788 and/or C3g in triode mode?
It's all in the datasheets.

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Ciao T
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Old 13th October 2011, 05:11 PM   #16547
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Hi John,

Quote:
Originally Posted by john curl View Post
Good to see you back, Thorsten. Just in time! Now we have some new material to work with.
Thank you, the new material is interesting (I had not realised just how rusty my Russian has become). I do think we still have some old material to cover, but I'm very much pushed for time ATM...

Ciao T
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Old 13th October 2011, 05:39 PM   #16548
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Quote:
Originally Posted by VladimirK View Post
For the KP903A the datasheet says
typical 0,7 nV/sqHz
Idss 300... 500mA
transcondactance 85 mA/V
Ciss = 18pF
dissipated power 6W
Would you kindly attach or link the datasheet? The combination of parameters does not seem real.
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Old 13th October 2011, 06:17 PM   #16549
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Just wait till he posts the transconductance numbers of the Crystalonics part.

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Last edited by jacco vermeulen; 13th October 2011 at 06:24 PM.
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Old 13th October 2011, 06:33 PM   #16550
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Quote:
Originally Posted by PMA View Post
Would you kindly attach or link the datasheet? The combination of parameters does not seem real.
Here is the CP650 datasheet

I would also like to mention, that kp903a are stable at SE output stage with 36V power supply, in spite that 20V are in datasheet. Even in industrial equipment, they work at 40V. I do not know, why the datasheet is so conservative. Moreover, I use the military specified version of these transistors, the 2P903A. Important difference between CP650 and kp903a, the last has all pins isolated from the stud mount case , while CP650 is not.
Attached Files
File Type: pdf CP650-653 n-chan 20V 0,6A 8W.pdf (98.5 KB, 75 views)

Last edited by VladimirK; 13th October 2011 at 06:40 PM.
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