I have found a wonderful explanation on adding resistor in series to CCS

Posted by Eric Chan (A) on May 1, 2024 at 09:25:10

In Reply to: CCS study in depth, what do you think this approach posted by Eric Chan on April 24, 2024 at 23:34:14:

Register / Login
Home
AudioAsylum Trader Audio Asylum Thread Printer
Get a view of an entire thread on one page

For Sale Ads
FAQ / News / Events

[ General ] [ Amp/Pre ] [ Speakers ] [ Hi-Eff ] [ Head ] [ Tubes ] [ SET ] [ OTL ] [ Tube/DIY ] [ Vinyl ] [ Cables ] [ Tweaks/DIY ]
[ Critics ] [ Digital ] [ Hi-Rez ] [ PC Audio ] [ Prop Head ] [ Iso ] [ Tape ] [ Tuners ] [ Vintage ] [ Music ] [ Classical ] [ Jazz ] [ Rock ]
[ Video ] [ Films ] [ Chat ] [ Reviews ] [ Inmate Systems ] [ Central ] [ Discount Dr. ] [ Shady ] [ Gallery ] [ Search ]

More Asylums
[ Asylum Support ] [ Forum Rules ] Find:

Tube DIY Asylum
Does a CCS work if placed in series with a plate resistor? (nt.)
203.94.155.130
[ Follow Ups ] [ Post Followup ] [ Thread: Display Email Next ] [ Tube DIY Asylum ] [ FAQ ]
Posted by Anthony Dockrill (A) on June 12, 2003 at 22:19:20

Follow Ups:
Yes, it has advantages. - VoltSecond 16:38:18 06/15/03 (1)
In Reply to: Does a CCS work if placed in series with a plate resistor? (nt.) posted by Anthony Dockrill on June 12, 2003 at 22:19:20:
I see I'm in the minority on the positive aspects of using a series CCS resistor.
A series resistor with the output of a CCS offers protection for the CCS. It is useful to limit current during arcs (tube and transformer), leading edges of shorts (oops, I shorted the output leads again), rapid reductions of the B+ (the B+ arced/ failed/ shorted or another tube on the B+ arced), the tube went into oscillation and other nasty oopses. 5 to 10% of B+ is a good starting point for the voltage drop on this resistor.

A series resistor also helps with stability of the CCS/ tube combination. At high frequencies the CCS appears as a capacitor and possibly a negative impedance if you are using a Hawksford cascode or if you have long leads (> 1 inch) on a standard cascode. This resistor buffers that capacitance (and negative impedance.) 1 to 5 times the current set resistor value is a good start point for this resistor value.

A series resistor helps when the CCS saturates. It softens both the recovery after saturation and at the start of saturation. 5 to 10% of B+ is a good starting point for the voltage drop again.

There are times when we don't need a series CCS output resistor, but they are fewer than what many would expect. It is easier to just design the resistor in, even if it doesn't drop as much voltage as the rules of thumb above. Sometimes the CCS damage from an arc is latent or just degradation in CCS performance, I don't want to risk that. This resistor doesn't have to be an expensive resistor either. A non-bargain basement metal film works pretty good.

Agreeing with somebody else's post, a resistor in the output is not a reliable way to reduce the voltage stress on the CCS. A resistor across the final CCS output stage is useful for reducing the power dissipation in the CCS. If you drop 20% of B+ on the CCS and 40% in the series resistor, when B+ drop 10% (the air conditioner kicked in, the neighbor's playing with big power tools again etc.) you now only have an output swing of two times 10% of B+ instead of two times 20% of B+. Now if the plate voltage bias point shifts up another 10% because of tube variations, we can't get any clean power out at all because the CCS is in saturation.

The negative comment on CCSs I get most often is "I replaced my output choke with a CCS and can't get any power out and the sound sucks." A CCS doesn't store energy like a choke. So the plate voltage can go down below B+, but not above B+. This is made worse by the CCS voltage drop.

CCS like to have voltage headroom. Both BJTs (rated > hundred volts) and FETs like to see several, if not 10s, of volts from base to collector (or gate to drain.) This is from both Early voltage and capacitive effects.

The plate voltage on CCS fed tubes tends to vary more than usual with CCS loading. Even with the CCS current set dead on. This is because the cathode to ground voltage for the tube is fixed (V = Iset * R_cathode) with CCS loading. It sort of looks like a battery from the cathode to ground!

When we have resistance between the B+ and plate, the tube current is allowed to change as the plate to cathode voltage changes. This is because the change in grid to cathode voltage (from the plate voltage variation) causes the plate current to change via the cathode resistor. This local feedback (from the cathode resistor) reduces the variation in plate bias voltage from tube to tube. With a CCS fed tube, the voltage across the cathode resistor is fixed so we don't get the local feedback.

So if you use a CCS, the B+ tends to be

B+ CCS estimate = Voltage cathode to ground + 2 * Voltage Plate to cathode at the tube's bias point + Voltage drop in the series resistor + 10% more.

This post is made possible by the generous support of people like you and our sponsors:

Follow Ups Full Thread

Topic - CCS study in depth, what do you think this approach - Eric Chan 23:34:14 04/24/24 (36)

my 2 pennies - Gordon Rankin 09:08:48 05/07/24 (3)

RE: my 2 pennies - Eric Chan 11:32:06 05/08/24 (2)

That Might be the Wrong Question - Triode_Kingdom 01:00:15 05/13/24 (0)

RE: my 2 pennies - Gordon Rankin 11:12:45 05/10/24 (0)

I have found a wonderful explanation on adding resistor in series to CCS - Eric Chan 09:25:10 05/01/24 (8)

Great find! - Paul Joppa 21:10:49 05/01/24 (7)

RE: Great find! - Eric Chan 00:14:28 05/02/24 (6)

RE: Great find! - Paul Joppa 14:02:35 05/03/24 (5)

I recall that Emotive is using CCS and tube voltage stabilizers to feed 12bh4a line stage - Wojciech 10:40:12 05/07/24 (4)

RE: I recall that Emotive is using CCS and tube voltage stabilizers to feed 12bh4a line stage - PakProtector 16:35:33 05/09/24 (2)

RE: I recall that Emotive is using CCS and tube voltage stabilizers to feed 12bh4a line stage - Wojciech 20:18:50 05/09/24 (1)

RE: I recall that Emotive is using CCS and tube voltage stabilizers to feed 12bh4a line stage - PakProtector 01:01:56 05/10/24 (0)

I use CCS feeding VR tubes at the ouput of my power supplies (preamp and driver stage supplies) - Tre' 10:54:28 05/07/24 (0)

RE: CCS study in depth, what do you think this approach - Eric Chan 23:25:46 04/25/24 (5)

RE: CCS study in depth, what do you think this approach - Paul Joppa 06:49:35 04/30/24 (3)

RE: CCS study in depth, what do you think this approach - Eric Chan 07:52:18 04/30/24 (1)

RE: CCS study in depth, what do you think this approach - Paul Joppa 12:06:20 04/30/24 (0)

RE: CCS study in depth, what do you think this approach - Eric Chan 07:47:11 04/30/24 (0)

You are using the resistor to buffer the CCS, so the plate (nt) - Chip647 08:37:12 04/29/24 (0)

SS simply isn't needed and I'l never do it - Triode_Kingdom 17:11:23 04/25/24 (7)

Lynn Olson used a lot of CCs circuits in his designs - Wojciech 10:44:36 05/07/24 (0)

RE: SS simply isn't needed and I'l never do it - Eric Chan 19:25:01 04/25/24 (0)

RE: SS simply isn't needed and I'l never do it - Tre' 18:56:36 04/25/24 (4)

RE: SS simply isn't needed and I'l never do it - Triode_Kingdom 09:22:47 04/26/24 (3)

RE: SS simply isn't needed and I'l never do it - PakProtector 14:40:29 04/27/24 (0)

RE: SS simply isn't needed and I'l never do it - Tre' 16:45:08 04/26/24 (1)

Got old Nait 3 and oh boy , say what you want but boring it is not by a long stretch - Wojciech 10:49:48 05/07/24 (0)

Try it for yourself and see if it makes a difference in your - Bas Horneman 02:03:05 04/25/24 (8)

RE: Try it for yourself and see if it makes a difference in your - Eric Chan 03:05:03 04/25/24 (7)

I'm just implying you should try it yourself.... - Bas Horneman 09:24:10 04/25/24 (6)

RE: I'm just implying you should try it yourself.... - Eric Chan 23:26:26 04/25/24 (5)

Junction 1k and tube plate.nt - Bas Horneman 05:52:10 04/26/24 (4)

RE: Junction 1k and tube plate.nt - Tre' 07:37:52 04/26/24 (3)

I know. But my answer was specifically tailored to his question. nt - Bas Horneman 07:47:16 04/28/24 (2)

I wasn't questioning your answer, just adding to it. even though no one ask me to :-) nt - Tre' 07:27:23 04/30/24 (1)

Thought so. Just wanted to be specific why I gave the answer I did. Thanks .nt - Bas Horneman 04:53:56 05/07/24 (0)

Follow Ups

I have found a wonderful explanation on adding resistor in series to CCS - Eric Chan 09:25:10 05/01/24 (8)

Great find! - Paul Joppa 21:10:49 05/01/24 (7)

RE: Great find! - Eric Chan 00:14:28 05/02/24 (6)

RE: Great find! - Paul Joppa 14:02:35 05/03/24 (5)

I recall that Emotive is using CCS and tube voltage stabilizers to feed 12bh4a line stage - Wojciech 10:40:12 05/07/24 (4)

RE: I recall that Emotive is using CCS and tube voltage stabilizers to feed 12bh4a line stage - PakProtector 16:35:33 05/09/24 (2)

RE: I recall that Emotive is using CCS and tube voltage stabilizers to feed 12bh4a line stage - Wojciech 20:18:50 05/09/24 (1)

RE: I recall that Emotive is using CCS and tube voltage stabilizers to feed 12bh4a line stage - PakProtector 01:01:56 05/10/24 (0)

I use CCS feeding VR tubes at the ouput of my power supplies (preamp and driver stage supplies) - Tre' 10:54:28 05/07/24 (0)

I have found a wonderful explanation on adding resistor in series to CCS

Post a Message!