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CCS with Cathode Resistor in a long tail ?

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Posted on September 18, 2016 at 15:18:52
multiblitz
Audiophile

Posts: 13
Joined: April 29, 2012
 Hi,

I have build originally

http://www.triodedick.com/monobill_2/monobill_2_schema_versterker.GIF

when doing tube-rolling, I got oscillations with his ccs, so I will change to Kevin's Compact CCS.

So first positive surprise if I got it right: I do not need the extra 15volt supply anymore, right ? Just plug the ccs into the circuit as if would be a resistor ?

So, my second question:

What about combining cathode resistor with a ccs in a long tail ? Like Allen sugested it here :

http://lh4.ggpht.com/_zjEUyEYa2J4/TSCzoDMHftI/AAAAAAAAB3g/FycjQFThnbI/pp_1c_s.gif

So, having some kind of local feedback from the resistor as well...any good ?

Later he changed it to two ccs...not sure why he did that: http://www.southampton.ac.uk/~apm3/diyaudio/PP-2C_schematic1.gif

Best Regards

Frank





 

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RE: CCS with Cathode Resistor in a long tail ?, posted on September 19, 2016 at 04:25:59
KevinC
Manufacturer

Posts: 2984
Location: NC
Joined: April 19, 2001
 Unfortunately, you would still need the -15V supply, in fact the Compact Cascode CCS would be returned to the -15V supply and there would be no ground connection as is shown in your existing schematic.

I have no idea why he used 470R cathode resistors and a common CCS. It's not something I have tried.

The change to two CCSs was probably so that the balance between the two halves of the driver could be precisely adjusted by means of the pot. I prefer to select matched triodes. 6N6Ps are cheap!

Kevin Carter
K&K Audio
www.kandkaudio.com

 

RE: CCS with Cathode Resistor in a long tail ?, posted on September 19, 2016 at 06:51:15
multiblitz
Audiophile

Posts: 13
Joined: April 29, 2012
 Thx for the fast reply...two questions:

1. In the current setup it is a positive +15V supply. Ate you saying I need to change it to -15V ?

2. Why 15 ? Why not 12 or 20 ? From where does this number come from ? Note that a 6n6 generates at 8ma -7.5v Ug while a 6922 would generate -4.1V Ug with the same current and 300v. I prefer the 6922 over the 6n6, more life-like.

Thx a lot.

Frank

 

RE: CCS with Cathode Resistor in a long tail ?, posted on September 19, 2016 at 09:40:01
KevinC
Manufacturer

Posts: 2984
Location: NC
Joined: April 19, 2001
 I'm sorry, but I should have caught the sign. It does need to be a negative voltage, and the greater the better, to a point. I don't hear any discernible improvement with more negative than -25V in my circuits.

In my 6N6P listening days I found that the tube sounded very much better at 20-25mA with about 150 volts cathode to plate. I can imagine it wouldn't be very exciting at 8mA, whereas the 6922 would shine at 7mA and 150V!

Just to confound you a bit more, I prefer the sound of balanced driver stages with current source plate loads and a simple unbypassed common cathode resistor. Of course, you can use a common cathode CCS connected to a negative supply, but then you need to add a load resistor to ground for each input tubs so you can set the plate voltage.

Kevin Carter
K&K Audio
www.kandkaudio.com

 

RE: CCS with Cathode Resistor in a long tail ?, posted on September 19, 2016 at 12:27:42
multiblitz
Audiophile

Posts: 13
Joined: April 29, 2012
 I forgot: will try of course the 6n6 at the bias you suggested...I like already its warm, nice tone, but would like more of the microdynqmics and speed of the 6922, if the 6n6 can get more dynamic/life-like, its near to my target.

What is your favourite tube as a driver for such an amp ? I guess you tried already much more than I did...

 

RE: CCS with Cathode Resistor in a long tail ?, posted on September 19, 2016 at 17:44:03
KevinC
Manufacturer

Posts: 2984
Location: NC
Joined: April 19, 2001
 I have adopted the Russian 6J49P pentode (triode connected) for a similar 2 stage PP amp kit (http://www.kandkaudio.com/power-amplifier/). The 6J49P and its similar relatives have somewhat higher gain (50) than the 6922 and are better able to cope with the higher voltage needed for tubes that have higher cathode bias voltages. I run the 6J49P at 14mA with a plate voltage of 190VDC. They impart an open, dynamic sound to the amplifier.

Kevin Carter
K&K Audio
www.kandkaudio.com

 

RE: CCS with Cathode Resistor in a long tail ?, posted on September 19, 2016 at 12:17:39
multiblitz
Audiophile

Posts: 13
Joined: April 29, 2012
 That was as well one of my thoughts...which version does sound better: Anode Load Ccs or Cathode Ccs...you answered it already...

I can imagine that you hear the same effect as Allen's Cathods ccs with resistors in between the cathode and the ccs. I did try this with a switch and with the resistors the sound is cleaner, stiffer, more precise...which I guess is the result of the local feedback of the cathode resistor. As not the whole Ug is generated by resistor, not all the gain is destroyed....my guestimate whats going on.

As I do habe four of your compact CCS I could indeed try the anode load as you suggested...

On your last comment:"...you need to add a load resistor to ground so that you can set the plate voltage" ...that is a bit to fast for me...do you have a schematic example ?

 

RE: CCS with Cathode Resistor in a long tail ?, posted on September 19, 2016 at 18:11:55
KevinC
Manufacturer

Posts: 2984
Location: NC
Joined: April 19, 2001
 If you wanted to use plate load CCSs and a common cathode CCS (connected to a negative voltage PS), one or the other of the current sources will not be serving as a current source as they can't be set so that the plate and cathode current values are exactly equal. If place a 100K resistor from the plate of each tube to ground, then the current through the input stage is the sum of those through the tubes and those through the resistors, but the current through the common cathode CCS is only the sum of the tube currents. You can then adjust the plate current sources so that the current through the 100K resistors sets the plate voltages. To make this clear I will have to devise a schematic with the details. It may not come soon, but I will try.


Kevin Carter
K&K Audio
www.kandkaudio.com

 

RE: CCS with Cathode Resistor in a long tail ?, posted on November 11, 2016 at 21:03:43
multiblitz
Audiophile

Posts: 13
Joined: April 29, 2012
 Hi,

...a schematic would be really helpful...

Just to take my specific case: I want to rund a diff. pair as phase-splitter and driver for a p-p El34/Kt120. This tube will be the 6N6p. As discussed, I would like to run it with 20-24ma per triode. Normally, It would have an Anode-Voltage of 390V, an Anode-Resistor of 10K. Currently your ccs is on the cathodes which are tied together for bothh system as diff. pair. Grid is grounded with a 47k resistor.

I am not sire where you would put the 100k resistor in your example ?

Best Regards

Frank

 

RE: CCS with Cathode Resistor in a long tail ?, posted on November 12, 2016 at 15:56:58
multiblitz
Audiophile

Posts: 13
Joined: April 29, 2012
 Or let me describe my thoughts and see if I understand it:

- I want the 6N6p to run at a Bias of 150V on the anode with 20 mA which requires -4,5V. currently my Load resistor is 10k, so with HV+ of350, it will drop the voltage from 350V to 150V and will produce heat of 0,02*200=4W each.

If I want now the same bias, the CCS needs to be set at 20mA. It would replace the Plate resistor with + goes HV and - goes Anode. Bias needs to be set by a resistor, normally to produce -4,5V this would mean R=4,5/0,02=225Ohm...as this resistor has two triodes to serve /diff pair), double current, so actually it should be 112 Ohm.

In the impasse-preamp the guy used LED to produce the negative voltage instead of a resistor...

Ok, back to the CCS. As we force with the negative grid voltage the operating voltage and with the ccs the current, the same 200V would drop over the CCS, correct ? So it would need to stand 4W.

If I now want to relief the CCS ( I am using the compact CCS with up to 2W), I could put a 5K resistor between the CCS and the Anode, so that 2W of the 4W in total will drop over that resistor and the other two over the CCS....correct ???

Any disadvantages ? Any wrong understanding ?

I found this setup as well here: http://www.audioxpress.com/article/The-ImPasse-Preamplifier ...R4 is the trick

Having this 5kresistor in place there will allow me to set the current as well...(still not sure how your 100k setup would work).

 

RE: CCS with Cathode Resistor in a long tail ?, posted on November 14, 2016 at 10:41:41
KevinC
Manufacturer

Posts: 2984
Location: NC
Joined: April 19, 2001
 Replied to your e-mail with a schematic file....

Kevin Carter
K&K Audio
www.kandkaudio.com

 

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