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Compact Current Source Kit

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Posted on September 21, 2009 at 18:23:55
JimBop
Audiophile

Posts: 1085
Location: Colorado Springs, CO
Joined: October 7, 2002
 I recently installed the Compact Current Source Kit in place of the plate load resistor on the 6SN7 tube in my 5Y3/6SN7/2A3 amps. Everything is working fine. Based on the math, I have it set at 6.0 mA. Does anyone have advice on fine tuning this device? What are the effects of increasing or decreasing the current settings?

Thanks in advance.

Jim D.

RE: Compact Current Source Kit, posted on September 21, 2009 at 19:09:35
KevinC
Manufacturer

Posts: 1999
Joined: April 19, 2001
Contributor
  Since: October 7, 2002
 The only way to do this so that you are optimizing the sonic performance of your amplifier is by making incremental changes in the CCS current (bias current) and listening for the difference with each change. I wouldn't be shy about adjusting the current in 1mA increments and listening to the differences. If you haven't done this before, you might be surprised with the magnitude of the audible differences.

In an ideal world, assuming that you don't change the cathode resistor value, as you increase the bias current, the plate voltage will drop and the cathode voltage will increase. Conversely, as you decrease the bias current, the plate voltage will rise and the cathode voltage will decrease. This also assumes that you have a fair amount of voltage drop across the CCS (say greater than 100VDC), so that it can operate properly over your bias current adjustment range.

Kevin Carter
K&K Audio
www.kandkaudio.com
RE: Compact Current Source Kit, posted on September 22, 2009 at 07:24:03
JimBop
Audiophile

Posts: 1085
Location: Colorado Springs, CO
Joined: October 7, 2002
 Any recommendations on how to do this with the boards in place and the amps running?

I was thinking of incremental 1/2-turn (or full turn) adjustments.

What is the best method for insuring that the two sides are matched and balanced? Should I measure final voltage at the plate?

Jim

RE: Compact Current Source Kit, posted on September 22, 2009 at 08:47:58
KevinC
Manufacturer

Posts: 1999
Joined: April 19, 2001
Contributor
  Since: October 7, 2002
 You can use the cathode resistor as a measuring tool to calibrate the current, by measuring the voltage drop across the resistor and using Ohm's law to calculate current. So measure the voltage to start, calculate the current, determine what current you want to adjust to, calculate the voltage necessary to result in that current and then adjust the trimpot until you achieve that current by arriving at the desired voltage.

Kevin Carter
K&K Audio
www.kandkaudio.com
RE: Compact Current Source Kit, posted on September 24, 2009 at 14:20:22
tuneful
Audiophile

Posts: 87
Location: New Mexico
Joined: October 29, 2004
 Here is the schematic of his amp as posted on the SET asylum:
Replacing resistors with Compact Current Source Kit, posted on September 24, 2009 at 17:20:10
KevinC
Manufacturer

Posts: 1999
Joined: April 19, 2001
Contributor
  Since: October 7, 2002
 Thanks! A picture is worth at least a thousand typed characters!

I would replace both the input triode plate resistor and the driver cathode follower with CCSs. Both will make a substantial sonic improvement in the amplifier.

Kevin Carter
K&K Audio
www.kandkaudio.com
RE: Replacing resistors with Compact Current Source Kit, posted on September 24, 2009 at 17:27:43
KevinC
Manufacturer

Posts: 1999
Joined: April 19, 2001
Contributor
  Since: October 7, 2002
 Looking more closely at the schematic, I wouldn't put the CCS where it's currently penciled in. In that position it will not allow proper operation of the cathode follower. The CCS belongs in the cathode of the driver.

I would also replace the 5Y3 rectifier with a lower impedance rectifier tube like a 5V4. The sound will be more dynamic.

Kevin Carter
K&K Audio
www.kandkaudio.com
RE: Replacing resistors with Compact Current Source Kit, posted on September 24, 2009 at 17:43:17
JimBop
Audiophile

Posts: 1085
Location: Colorado Springs, CO
Joined: October 7, 2002
 Kevin,

I discovered that there are two mistakes on the schematic:

- The 100K resistor from pin 1 of the 6SN7 should connect to the next line to the right (the output of the CCS).

- I missed a jumper and 522K resistor between pins 2 and 6 of the 6SN7.

Getting back to your comments, it seems I have placed the CCS in the wrong position. Exactly what resistor should it replace? The 100K on Pin 1?

Where should the 2nd CCS be installed?

Jim
RE: Replacing resistors with Compact Current Source Kit, posted on September 25, 2009 at 06:36:03
KevinC
Manufacturer

Posts: 1999
Joined: April 19, 2001
Contributor
  Since: October 7, 2002
 You should replace the 100K plate resistor for the input half of the 6SN7GT with a CCS. The second CCS should be installed in place of the 33K cathode resistor in the cathode follower driver.

Kevin Carter
K&K Audio
www.kandkaudio.com
RE: Replacing resistors with Compact Current Source Kit, posted on September 25, 2009 at 06:42:51
JimBop
Audiophile

Posts: 1085
Location: Colorado Springs, CO
Joined: October 7, 2002
 Thanks Kevin. I appreciate your help.

I'm learning (slowly).

Jim

RE: Compact Current Source Kit, posted on September 22, 2009 at 22:03:36
JimBop
Audiophile

Posts: 1085
Location: Colorado Springs, CO
Joined: October 7, 2002
 Most of this makes sense, but I'm new to this, so I have more questions.

Will the current that I calculate at the cathode resistor be equal to the current setting of the CCS? Or will it be a different current value that I will use as a benchmark for adjusting the current of the CCS?

For example: The CCS is presently set for 6mA; and let's say I want to increase it to 7mA.

Will the current at the cathode resistor also be 6mA? (I'm guessing it won't be.) So, once I have determined the actual current at the cathode resistor, would I then determine what voltage is necesarry to increase it by 1mA so that the current at the plate with also increase by 1mA?

Jim

RE: Compact Current Source Kit, posted on September 22, 2009 at 09:30:25
Tre'
Industry Professional

Posts: 4846
Joined: February 9, 2002
 Sorry for stealing the threat,

Will the CCS stay stable at low current? Down to 1ma?

Thanks, Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
RE: Compact Current Source Kit, posted on September 22, 2009 at 09:36:00
KevinC
Manufacturer

Posts: 1999
Joined: April 19, 2001
Contributor
  Since: October 7, 2002
 I use them in a microphone application at 1mA and have had no instability problems.

Kevin Carter
K&K Audio
www.kandkaudio.com
RE: Compact Current Source Kit, posted on September 22, 2009 at 10:24:56
Tre'
Industry Professional

Posts: 4846
Joined: February 9, 2002
 Thank you Kevin.

One more question please, do you use gate stop resistors? I only see one of on the Cascode current source kit. It looks like there are two on the Compact Cascode current source kit.

I will be trouble shooting a phono preamp with wandering plate voltages that I think uses the Cascode current source kit. At this point, sense I don't have the preamp yet, I'm just pre-thinking.

Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
RE: Compact Current Source Kit, posted on September 22, 2009 at 12:51:12
KevinC
Manufacturer

Posts: 1999
Joined: April 19, 2001
Contributor
  Since: October 7, 2002
 There are two gate stoppers in all of the cascode CCSs.

Kevin Carter
K&K Audio
www.kandkaudio.com

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