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EL84 SE auto bias

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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
 
The design I am making is this



EL84_SE_ECC81.gif



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

attachment.php


and

http://www.diyaudio.com/forums/showthread.php?s=&threadid=72536&highlight=baby+huey
 
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
 
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?:hot:
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.
 
kooltubes said:
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?:hot:
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.
:hot:
 
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:bigeyes:
 
kooltubes said:
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:bigeyes:

When u feed more current . First the vocal sound thicker. Than u have better soundstage. Get rid of the 22mf in pin 2 not required it will create different sound, best if we do not use caps at all but cant help it as we need it here & there .I have tried it with value from 65 - 100ma and i think it sound best at 100ma.
 
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