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Old 8th September 2008, 12:06 PM   #1
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Default help for E182CC linestage/driver

Hi,

I need your precious help to start my experimentations
with a single (half R, half L) common cathode ,automatic bias.
B+ is 210 V or up to 250 Volt disponible
Requested Z out as low as possible ( 1200-1300 ohm ? )
'' output swing 10 volt rms with decent THD
So I need the value of the plate resistor and the cathode resistor
If my Siemens E182CC will be microphonic, i'll swap for a 6N6P
Thanks for your comments !

Paolo
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Old 8th September 2008, 11:11 PM   #2
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Paolo,

Start with the data sheet. RP is approx. 1.6 KOhms. Get the superior O/P drive you crave by DC coupling an IRFBC20 source follower to each of the common cathode gain stages. With buffering, 4.7 KOhm load resistors should be enough.
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Old 8th September 2008, 11:26 PM   #3
Gordy is offline Gordy  United Kingdom
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Paolo,

Do you really need 10V RMS? That is about 28V peak-to-peak, and it seems a lot.

My advice is to make the first step: define your requirements very clearly...

> what is the amplitude of the input signal?
> what is the output impedance of the source equipment?
> what is the output amplitude required from your stage? (Really 10V RMS?)
> what is the input impedance of the target equipment?
> do you need volume control / attenuation?
> what is the impedance of the cables from output of your stage to the target equipment ? (The total capacitance may matter)
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Old 9th September 2008, 09:12 AM   #4
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Hi Gordy,

Yes i need it because I have to drive this:

http://www.audiodesignguide.com/Powe...wer/index.html

Now I use a different IRF540 or IRFP140 with half Ciss approx.

Now I use a 6922 cathode follower but I am not satisfied, I want try
the SE mode. The gain is enough for me, not important.
Not fanatic of thd also, I hope less 1% is ok.
Today I have found this schematic :

http://www.jenisonaudio.i8.com/pages/6n6prebuild.html

but I have not idea of the output impedance or the THD

Do you think it is ok or need to be pushed more hard ( more current?)
I am total incompetent in electronics so I need your expertise to obtain
my targets.

My source is an old Aragon D2A DAC. output impedence is 300 ohms
I have a 100K pot at the input of the tube.
My cable is a bifilar type ( not coax) Monster cable M1500 1 meter

Cheers,

Paolo
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Old 9th September 2008, 03:05 PM   #5
Gordy is offline Gordy  United Kingdom
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I think the guy from the jenisonaudio site is here on DiyAudio, somewhere.

I am not an expert on loadlines, but looking at the information in the 6N6 link: http://www.mif.pg.gda.pl/homepages/f...113/6/6N6P.pdf

...with 300V supply, 10K anode load, and a 100 Ohm cathode resistor... it should be in the region of 100V on the anode and flowing 20mA, with a cathode (/bias) voltage of 2V.

You may need to bypass the cathode resistor to get the output impedance down and obtain the gain you desire.

Remember that 6N6 requires 750mA for the heater.

Interesting general vacuum tube information here:
http://www.aikenamps.com/ (section: tech info)
http://www.turneraudio.com.au/index.html (sections: preamplifiers, educational+diy)

Also, consider reading the Morgan Jones book on Valve Amplifiers.
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Old 9th September 2008, 03:12 PM   #6
Gordy is offline Gordy  United Kingdom
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The 6N6 tube looks very linear at that operating point, so your THD should be fine.

Quote:
Originally posted by inertial
DAC. output impedence is 300 ohms
I have a 100K pot at the input of the tube.
300 into 100K is ideal.

: )
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Old 9th September 2008, 03:14 PM   #7
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I'm here and would also suggest bypassing the cathode resistor. For me its not much of a worry with the load I'm driving. Oddly enough I can hear a big difference between the 6N6P and 5687, but not much of one between the 6N6P and a DIY 'Bride of Zen' preamp.

I'll also note that my 6N6P preamp was a quickie build based on a 5687 design. I never went through the pains of optimizing it - I just wanted to hear what the 6N6P sounded like.
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Old 9th September 2008, 03:46 PM   #8
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Hi

Thanks Gordy, yes cathode bypass of course

Oh thanks Kewin, sometimes the world is so little !
Optimization, yes this is my problem, at the moment I want start with my E182CC and have 250V only. I was in searching confirmations
on that operating point.
But 20mA on each section is a big current, am I right guys?
What is (approx) the output impedance?
Is it the grid stopper a bit big ?
Cheers,

Paolo
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Old 9th September 2008, 04:57 PM   #9
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Location: Italy
One more,

To be totally honest I have also the final target to change the actual
PSU for a PSU a'la Thorsten Loesch

( please see the "universal valve power supply" schematic)
http://www.fortunecity.com/rivendell...da/vasfda.html

I have a trafo ok for that schema. I need only the chokes.
But It is only 210V B+
So I have to choice ......my mistake........ Can I try with only 210V?
Maybe I'll have too much THD. Maybe better lowering a bit the current also. And the Zout ?

Excuse for my confusion

Paolo
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Old 9th September 2008, 06:46 PM   #10
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Hi,

keeping it simple,

half E182CC

Code:
B+ 300volt     anode load 10k    cathode resistor 100          rejected
B+ 250volt     anode load 10K    cathode resistor 100        supposed OK
B+ 210volt     anode load  ?     cathode resistor  ?              THD?

Thanks for all the comments, I really appreciate your help

Cheers,

Paolo
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