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CCS Current Set Question

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Posted on September 15, 2020 at 11:12:21
Chip647
Audiophile

Posts: 2652
Location: The South
Joined: December 24, 2012
 When using a CCS as a plate load, which of the three options is best/standard:

1. Run the CCS a few mA above the current draw of the tube

2. Try to precisely match the current draw of the tube to the CCS regulation

3. Run the tube so that it is in a slightly starved condition, i.e. if the tube would be drawing 5mA with a 1k cathode resistor at 200v on the plate, set it so the CCS runs at 4mA with the 1k cathode resistor and 200 plate

 

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RE: CCS Current Set Question, posted on September 15, 2020 at 11:53:43
Paul Joppa
Industry Professional

Posts: 7296
Location: Seattle, WA
Joined: April 23, 2001
 You don't get a choice. If you run the current high, the plate voltage will rise until the tube consumes the current.

That's why you usually don't see CS loads on pentodes.

 

The output current of the CCS should be what the design calls for on the plate, posted on September 15, 2020 at 11:55:45
richardl
Audiophile

Posts: 3555
Joined: September 5, 2002
 The CCS is just there to fix the current(It is set to a certain value) and add a high impedance to the plate. Running the tube hot will make it more linear oftentimes. Running it cool makes them last longer and oftentimes less linear. The part about linearity is extremely altered by the CCS since the line drawn in the tube graph(current vs voltage) is straight across rather than from Max current(zero volts) to zero(at plate voltage max.)

 

RE: CCS Current Set Question, posted on September 15, 2020 at 15:34:35
Tre'
Industry Professional

Posts: 17302
Location: So. Cal.
Joined: February 9, 2002
 Whatever current you set the current source to, that's how much current will flow through the tube.

I set my current sources using a low voltage (maybe 50 volts or so) bench supply. When I put them in the circuit they are always right where I set them.

If you want a particular plate voltage, change the cathode resistor. A larger cathode resistor will increase the plate voltage and a smaller cathode resistor will lower the plate voltage but the current through the tube will always be the same as the current through the CCS. The current that you set.

Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"

 

RE: CCS Current Set Question, posted on September 16, 2020 at 04:56:50
dave slagle
Manufacturer

Posts: 5430
Location: NYC
Joined: April 27, 2001
 That's why you usually don't see CS loads on pentodes.

not that i condone such behavior but try telling that to JC :-)

dave

 

RE: CCS Current Set Question, posted on September 16, 2020 at 07:50:47
PakProtector
Audiophile

Posts: 12364
Joined: May 14, 2002
 I think I would take a slightly simpler means of delivering the gain. Also, not quite sure why JC is running the 2540 instead of the 3545 for the lower element. The 10M90 is a brilliant swap vs a 2540 on top; it gives the lower FET 2x the d-s voltage to work under.

IOW, ccs to plate load the pentode. Resistor from plate to ground to set gain/load line. Output on the mu/lower source of the ccs. Can set the g2 voltage a few ways, I do kinda think JC's is preferable to mine...except when building a LTP and want the g2 node ref'd to the cathode node and not ground, without having to arrange a shunt reg, and then pass ALL the current through the cathode circuit.
cheers,
Douglas

Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.

 

RE: CCS Current Set Question, posted on September 16, 2020 at 08:12:24
Paul Joppa
Industry Professional

Posts: 7296
Location: Seattle, WA
Joined: April 23, 2001
 Thanks for the link - I didn't know he had a site.

Yeah, I've done pentodes with CS loads too, it's just a little more complicated.

 

Thanks Everyone!, posted on September 16, 2020 at 14:34:55
Chip647
Audiophile

Posts: 2652
Location: The South
Joined: December 24, 2012
 I really appreciate the insight!

 

RE: CCS Current Set Question, posted on September 17, 2020 at 10:37:47
kobasa@xs4all.nl
 Dos JC's penthode act as a penthode or more like triode because of the feedback?

 

RE: CCS Current Set Question, posted on September 17, 2020 at 11:47:03
dave slagle
Manufacturer

Posts: 5430
Location: NYC
Joined: April 27, 2001
 He has gotten 60dB of gain out of a single stage so I'd wager pentode :-)

dave

 

RE: CCS Current Set Question, posted on September 17, 2020 at 12:05:20
kobasa@xs4all.nl
 sounds nasty.
How do they say it in USA? NEXT?

 

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