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Old 31st March 2007, 09:48 PM   #1
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Thats a weird glich, no wonder no one was responding......


okay, well I am currently constructing an EL84 SE amplifier, and I am using an LM317 as a CCS for biasing each tube (one LM317 per channel) and I wanted to know what would happen if I didn't bypass them with capacitors, I have seen several CCS bias designs that do not use bypass capacitors (none of them SE), and I wanted to know what the DIY Audio community thought.

-Moose
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Old 31st March 2007, 10:10 PM   #2
d2134 is offline d2134  Romania
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Quote:
I have seen several CCS bias designs that do not use bypass capacitors
Please post some schematics or links.
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Old 31st March 2007, 11:39 PM   #3
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The design I am making is this



Click the image to open in full size.


I have mostly seen non-bypassed designs on Push-pull stuff, but I did not know if it would carry over, here are some designs that do not include it


http://www.diyparadise.com/buildel84b.html

Click the image to open in full size.

and

EL84 Amp - Baby Huey
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Old 31st March 2007, 11:55 PM   #4
d2134 is offline d2134  Romania
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In the case of Baby-Huey:
On general schematic is drawn a "bias block". On the second page we notice the bias block in detail. It has the actual CCS (the 2 tranzistors + rezistors) and the bypass capacitors (4700uF+470uF+1uF) parallel for good frequence response. This is a good practice.

In your case you have to bypass the LM317 based CCS in a similar way
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Old 1st April 2007, 12:02 AM   #5
d2134 is offline d2134  Romania
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In the case of LED array:
it is NOT a CCS. The LED array is a fix voltage biasing element. Like a zener diode with hight current.
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Old 1st April 2007, 12:09 AM   #6
d2134 is offline d2134  Romania
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The case of Simple EL84 is a litle special. We have an auto phase invering final stage. We notice one valve grid is grounded. In this case the CCS must be NOT bypassed. The signal for the lefthand pentode is applied on grid and for the righthand pentode is applied in cathode. Search the net for "long tail pair" for more details. http://www.aikenamps.com/LongTailPairDesign.htm
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Old 1st April 2007, 03:04 AM   #7
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wow, thank you, i'll be sure to bypass those now

-Moose
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Old 5th April 2007, 11:46 AM   #8
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I have just built a El84SE using an LM317 in lieu of the cathode bias resistor.
The voltages are correct, but the amp is mute...any idea?
Pin 1(adj) is grounded; 23.2 ohms from Pin 2 (Vout) to ground; Pin 3(Vin) is tied to the El84 cathode.
I have read in this thread that the LM317 needed to be bypassed, what is the cap value and do I connect it from Vin (pin 3) to ground?

Your help is much appreciated.
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Old 5th April 2007, 02:50 PM   #9
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Quote:
Originally posted by kooltubes
I have just built a El84SE using an LM317 in lieu of the cathode bias resistor.
The voltages are correct, but the amp is mute...any idea?
Pin 1(adj) is grounded; 23.2 ohms from Pin 2 (Vout) to ground; Pin 3(Vin) is tied to the El84 cathode.
I have read in this thread that the LM317 needed to be bypassed, what is the cap value and do I connect it from Vin (pin 3) to ground?

Your help is much appreciated.
Your ccs is correct, you also have 50ma .As to the bypass caps. U can try it out any value from 47 -470 . U may also want to try higher current, its sound sweeter. Try 12R its tasty.
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Old 7th April 2007, 11:50 AM   #10
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Thanks SINGLEENDED.

Amp works fine. I have used different cap values but 100mf sounds better to my ears.
I have also added 22mf betwwen Vout (pin 2) to ground, the soundstage seems to be scaled down.

I am confused about your suggestions to run the El84 at 104ma using a 12R resistor
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