cf topology lessons... pls help
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JojoD818
diyAudio Moderator

Join Date: Mar 2003
Location: searching...
cf topology lessons... pls help

Hi guys!

I built the circuit below using the part values indicated in the schematic from an old publication. First of all it works, I measure a B+ of 148.8VDC at the plate to ground of the tube and 4.2VDC from cathode to ground (across 22K).

Can anyone give me the mathematical formula for computing the gain of this circuit?

How do I choose the value of the cathode resistor if I will use different tubes? I would like to learn how to effectively use the graphs in tube datasheets for this particular circuit.

JojoD

PS, I know the supply is a bit low but this is an experiment and I don't want to blow things up especially my tubes.
Attached Images
 test tube.jpg (8.5 KB, 343 views)

 29th April 2004, 11:38 AM #2 Alastair E   diyAudio Member     Join Date: Feb 2004 Location: South Wales CF Generally speaking, Cathode Followers have no, or a slight reduction in gain, What they do have is the ability to match up a high impedence source to a lower imp load. If you need gain, you could precede this stage with a common cathode gain stage using the other half of the 6N1p __________________ Das Beste Oder Nichts
JojoD818
diyAudio Moderator

Join Date: Mar 2003
Location: searching...
Re: CF

Quote:
 Originally posted by Alastair E Generally speaking, Cathode Followers have no, or a slight reduction in gain, What they do have is the ability to match up a high impedence source to a lower imp load. If you need gain, you could precede this stage with a common cathode gain stage using the other half of the 6N1p

But how do I choose the cathode resistor for optimum tube performance?

 29th April 2004, 01:18 PM #4 s2kov   diyAudio Member     Join Date: Mar 2004 Location: AB JojoD, You have to determine first your operating point of the tube you will use. By then, you can compute for the value of cathode resistor. Of course, Ohm's Law will always be here....
JojoD818
diyAudio Moderator

Join Date: Mar 2003
Location: searching...
Quote:
 Originally posted by s2kov JojoD, You have to determine first your operating point of the tube you will use. By then, you can compute for the value of cathode resistor. Of course, Ohm's Law will always be here....

Please elaborate. Let's use the 6N1P tube as an example for this exercise.

s2kov
diyAudio Member

Join Date: Mar 2004
Location: AB
I don't have datasheet for 6N1P.... But assuming you're using Plate Voltage and Current of 148V and 15mA respectively. Corresponding bias voltage is, say, -6V then you can compute for Rk using this formula:

Rk = Vg/Ia

Where:

Rk = Cathode Resistor
Vg = Grid Voltage
Ia = Plate Current

Please note that above figure is just an assumption, just focus on the above formula base on your operating point that will be used.

Tube Gurus,

Please correct me if i'm wrong....

Quote:
 Originally posted by JojoD818 Please elaborate. Let's use the 6N1P tube as an example for this exercise.

JojoD818
diyAudio Moderator

Join Date: Mar 2003
Location: searching...
I hope this can help us in this exercise...
Attached Images
 6n1pspec.jpg (38.3 KB, 252 views)

 29th April 2004, 04:44 PM #8 ErikdeBest   mostly thinkerer diyAudio Member   Join Date: Mar 2003 Location: Zürich Something like this? Given: 300V on plate bias 15mA 4V / 15mA Rk = 266R Try to search for grounded cathode amplifier at www.tubecad.com.
 29th April 2004, 06:04 PM #9 s2kov   diyAudio Member     Join Date: Mar 2004 Location: AB Another one: Plate Voltage = 200V Plate Current = 10mA Grid Voltage = -2V Rk = 2/0.01 = 200R Hope this help....
ErikdeBest
mostly thinkerer
diyAudio Member

Join Date: Mar 2003
Location: Zürich
Quote:
 Originally posted by s2kov Another one: Plate Voltage = 200V Plate Current = 10mA Grid Voltage = -2V Rk = 2/0.01 = 200R Hope this help....
This settings would be better, as the maximum anode voltage is 250VDC (from the datasheet)

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