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Old 16th September 2013, 04:09 PM   #1
Green77 is offline Green77  Sweden
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Default Will this work? (EL34 PP)

Hi all!

I bought a PCB from Ebay for a standard EL34 PP amp. I have built those before so i thought if i could improve it with a ccs. I really have no idea what i'm doing but I have built with ccs before (TubelabSE) but never understand how it works.
Anyway..

Click the image to open in full size.

Will this work? Will it improve the amp? Before it was a 22K resistor.
How should i know what mA i want from the css? Is it correct calculated that this will draw 6mA totally (3mA per side)?

Sorry for all the questions...

Regards //Daniel
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Old 16th September 2013, 04:23 PM   #2
TheGimp is offline TheGimp  United States
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What are the values of B1+ and B2+ ?
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Old 16th September 2013, 04:28 PM   #3
SY is offline SY  United States
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Quote:
Originally Posted by Green77 View Post
I bought a PCB from Ebay for a standard EL34 PP amp. I have built those before so i thought if i could improve it with a ccs. I really have no idea what i'm doing but I have built with ccs before (TubelabSE) but never understand how it works.
Run, do not walk, and get a copy of Valve Amplifiers 4th edition. In it you will find full explanations of CCS and why you can't drop it into the circuit without changing some plate resistors. I'd guess from the values there that the original cathode resistor was about 18k.
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Old 16th September 2013, 04:32 PM   #4
Yvesm is offline Yvesm  France
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It should work a bit better: improved symetry to drive the power stage, you may like or dislike (less even harmonics generated).

Your emiter resistor is correct for 2 x 3mA, just keep in mind that the MjE340 will have to sustain about 140V and will dissipate near 1 Watt.

Yves.

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Last edited by Yvesm; 16th September 2013 at 04:37 PM. Reason: Comment 'cos cross posts by SY
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Old 16th September 2013, 04:36 PM   #5
SY is offline SY  United States
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Quote:
Originally Posted by Yvesm View Post
improved symetry to drive the power stage
Not with the plate resistors on the schematic- this will be more unbalanced than the original since the tail is too good. Changing the plate resistors to equality will bring things back in line. The feedback here is way too low as well.

Of course, that doesn't change my recommendation that the O/P try to understand the "why" better.
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Old 16th September 2013, 04:39 PM   #6
Yvesm is offline Yvesm  France
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Your right on both points, sorry for having read too fast
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Old 16th September 2013, 05:07 PM   #7
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So strict balancing does not matter, in terms of sound quality. :-)

CCS load of V2a may help more.
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Old 16th September 2013, 05:10 PM   #8
Green77 is offline Green77  Sweden
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Thanks all for your answers!
I will get the bibel ( 4th edition..) read it, and try to understand it but i want to understand, order parts and build now!!
Ok, so the anodresistors need to be equal. And in the original schematic the resistor was 22k so it was close SY
B+ will be 450v then drop 2.2k for B1 and 150k to B2.
Fine that i got the emiter resistor right..(for 6mA, if that is correct?)! Always a start..

Regards //Daniel
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Old 16th September 2013, 05:13 PM   #9
SY is offline SY  United States
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Old 16th September 2013, 05:44 PM   #10
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"Valve Amplifiers 4th edition"

should i start with 1st edition? or is it just a update?
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