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Old 16th March 2013, 10:19 PM   #1
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Default Help with DN2540 CCS design

I want to build a CCS as a plate load for a 6SN7 so that I can get a 250 v pp swing with low distortion. It looks like 5 or 6 ma would be about right for my application.

The CCS circuit used in the plate loads shown in this SCHEMATIC use a pair of DN2540s. (My apologies to SY for purloining his drawing). I'm unclear to me how the circuit works and am unable to determine if the current can be sized down to the 5 ma target and what resistor value would be required. I can guess about 600R but I'd prefer to understand it a little better.

Can someone explain the circuit and math of sizing the resistors, please.
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Old 16th March 2013, 10:55 PM   #2
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What are R3 and R12 for? They serves no purpose. They are not grid stoppers. The LEDs in the cathodes will produce bias problems. Why wire a pentode that has lots of mU as a triode and if the neon strikes, (NE) the grid/cathode will be damaged.
Not for me, sorry.
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Old 16th March 2013, 11:13 PM   #3
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You can read about the amplifier design HERE. The article documents the design quite well.

This thread is about the DN2540 CCS circuit used in the plate load.

Last edited by Captn Dave; 16th March 2013 at 11:15 PM.
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Old 16th March 2013, 11:31 PM   #4
SY is offline SY  United States
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The DN2540 cascode is not a great choice for low currents (under 10mA). A bipolar cascode would work considerably better. There's a very detailed description and design equations in Morgan Jones's "Valve Amplifiers."
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Old 16th March 2013, 11:41 PM   #5
Matt BH is offline Matt BH  United Kingdom
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I had the same question a few years ago. Si is spot on, arm your self with a copy of Morgan Jones truly excellent book and build your self a CCS using whichever topology you fancy and measure it. Honestly playing about is the way to learn.

Cheers.
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Old 16th March 2013, 11:46 PM   #6
Matt BH is offline Matt BH  United Kingdom
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Sorry, what do you need 250V peak to peak for?
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Old 16th March 2013, 11:48 PM   #7
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diytube.com • View topic - EZ Sink: Depletion-mode MOSFETs and the LM334
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Old 16th March 2013, 11:54 PM   #8
Matt BH is offline Matt BH  United Kingdom
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Nice link. 334 is a bit crappy though don't you think?
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Old 17th March 2013, 12:17 AM   #9
Matt BH is offline Matt BH  United Kingdom
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Doh, I didn't fully read it. Balls, sorry. I instantly thought bandgap referenced crap. Have to admit I have never used the 334. It does look bloody good.

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Old 17th March 2013, 01:20 AM   #10
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Quote:
Originally Posted by SY View Post
The DN2540 cascode is not a great choice for low currents (under 10mA). A bipolar cascode would work considerably better. There's a very detailed description and design equations in Morgan Jones's "Valve Amplifiers."
Yes SY, the discussion around fig. 2.50 and 2.51 in MJs third edition is essentially my application. No doubt, that's where the idea came from. I don't have a copy of the fourth edition; has Mr. Jones updated his solid state plate load discussion with newer ss devices?

I find the DN2540 circuit, such as used in your schematic, a bit more efficient and would prefer to experiment with it were it not for the low current limitation you describe. Also with B+ near 450 and plate voltage in the 250v range, I'm just a little concerned about smoke at startup.

Matt - this would be a second stage to drive an 845. A cathode follower would make the third stage.

Counter culture - thanks for that link! Have you seen a similar scheme for a source?

Last edited by Captn Dave; 17th March 2013 at 01:27 AM.
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