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Old 19th February 2009, 05:03 PM   #1
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Default chocke anode load, please explain me..

Hi guys,

Suppose I have a 6N6P , B+ is 200 Volt, bypassed cathode resistor is 100 ohms, anode resistor is 5,6 K .

In this situation , gain is 13,5X ( into 100K) and since Rp is about 1600 ohms, probably output impedance is to say, 1400 ohm. Current is about 20 mA for each section.

( this is my beloved driver stage....:-) )

What happen if I swap the anode resistor with a good 60H choke?

Gain? approx
Output impedance? approx

Perdone my basic questions, but I am a newbie on tubes and I would be learn

Very thanks!

Cheers,
Paolo
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Old 19th February 2009, 05:17 PM   #2
Gluca is offline Gluca  Italy
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The anode resistor is dropping 5.6*20=112V, if you replaced that R with a choke your tube would be exposed to a much higher anode voltage. You need to lower it before replacing the R!

60H at 20Hz have an impedance of 2*3.14etc...*20*60=7.5K so you will have a bit more gain. Output impedance won't change, sound should improve (that's my taste).

Even better would be a proper CCS.

Gianluca
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Old 19th February 2009, 06:25 PM   #3
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Quote:
Originally posted by Gluca
The anode resistor is dropping 5.6*20=112V, if you replaced that R with a choke your tube would be exposed to a much higher anode voltage. You need to lower it before replacing the R!
Yup, understood, thanks Gianluca! :-)


Quote:
[i]
60H at 20Hz have an impedance of 2*3.14etc...*20*60=7.5K so you will have a bit more gain. [/B]
Ok, How can I calculate this little "more" ?
No possible go to near the mu of the tube ( 22 about)?

Quote:
[i]
Output impedance won't change, sound should improve (that's my taste). [/B]
oh, what a delusion! :-(


Quote:
[i]
Even better would be a proper CCS.

Gianluca [/B]
But this CCS lower the output impedance , am I right?

thanks,
Paolo
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Old 19th February 2009, 06:52 PM   #4
Gluca is offline Gluca  Italy
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You can go up to gain=mu using a CCS (that looks like a very-very large resistor). The output impedance can be lowered using the CCS-tube combo as a mu-follower. I believe a schematic can help.

My preamp

Google "gary pimm" and "walt jung" for some very interesting documents on CCS'. Many many pages have been written here too.

OH! I loved 6N6s. One of the best things I soldered was a mufollower made by 6N6+EF184

Ciao
Gianluca
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Old 19th February 2009, 07:00 PM   #5
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Thanks Gianluca,

Indeed I am more incline to Chocke instead CCS

Anyway, back to the "little more" gain question, are we speaking about 1 dB ? Better than nothing !
But this mean that the more the chocke is bigger, the more the gain I will obtain?

i also love the 6N6-P : IMO it is awesome "tubey" , very different from to say, a ECC88, 5842, etc . I am really impressed by 6N6-P.
I have to thanks this TUBES section for this thing!

Cheers,
Paolo
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Old 19th February 2009, 07:14 PM   #6
Gluca is offline Gluca  Italy
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Quote:
Originally posted by inertial
Thanks Gianluca,

Indeed I am more incline to Chocke instead CCS

Anyway, back to the "little more" gain question, are we speaking about 1 dB ? Better than nothing !
But this mean that the more the chocke is bigger, the more the gain I will obtain?

Cheers,
Paolo

CCS' actually outperform chokes. Keep in mind chokes usually have higher stray capacitance that impairs hi-freq (is that a problem really? we are talking >50kHz), and CCS will give you lower distortion (does it matter? probably not). The bigger the choke the heavier the iron the higher the price the worse the hi-freq behavior. CCS' can offer also a better rejection of PSU's noise. And cost 1/10 of a good choke.

The choke's impedance goes up with frequency, I calculated the value at 20Hz to make sure 60H are enough otherwise low frequencies would be compromised. I believe you won't notice any difference of gain between CCS and chokes (but at low frequency).

OH! I do use chokes as necessary.

Ciao
g
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Old 19th February 2009, 10:44 PM   #7
Tweeker is offline Tweeker  United States
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The advantage of a choke is its energy storage, a CCS must drop whatever volts your planning to swing across it, along with some headroom drop across the CCS parts itself. CCS is a variant of resistive load.

Choke vs CCS on the same B+ will involve different operating points, as mentioned.
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Old 20th February 2009, 11:47 AM   #8
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Thanks Gianluca and Tweeker
Things are more clear for me now

Cheers,
Paolo
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