One big problem when it comes to CCS´s seems to be the lack of PNP/P-channel devices that can handle the voltages associated with tube circuits.
The CCS that Nelson uses in his amps has one N-Mosfet and one NPN transistor. If those devices were replaced by high voltage types and some resistors and caps were changed it should work as a plate load for SE triode output stages, right?
One more thing: The Alephs CCS is dynamic (it somehow mirrors the output current which increases the efficiency), how would this affect the tube?
The CCS that Nelson uses in his amps has one N-Mosfet and one NPN transistor. If those devices were replaced by high voltage types and some resistors and caps were changed it should work as a plate load for SE triode output stages, right?
One more thing: The Alephs CCS is dynamic (it somehow mirrors the output current which increases the efficiency), how would this affect the tube?
Take a GOOD look at Gary Pimm's CCS designs. They provide a load in the GOhm range and offer a mu follower O/P whose use is optional. While GP's SS circuitry can handle several hundred Volts, if really high voltage compliance is needed, a pentode can be added to the SS circuitry.
The URL for Gary Pimm's web site is (http://home.pacifier.com/~gpimm/).
The URL for Gary Pimm's web site is (http://home.pacifier.com/~gpimm/).
I have no doubts that Gary´s stuff is great, but what I´m looking for is something simple.
Here is another CCS topology that I´ve seen at a few places. Could it be something?
http://w1.223.telia.com/~u22306942/HORLURSFORSTARKARE.pdf
Here is another CCS topology that I´ve seen at a few places. Could it be something?
http://w1.223.telia.com/~u22306942/HORLURSFORSTARKARE.pdf
That circuit is a mu follower. It should perform well. If you decide to replicate that design, be sure to use a 6922 with closely matched sections.
What is the difference between a CCS loaded triode stage and a mu-follower?
I have no plans for biulding that circuit as it is (a headphone amp),
but the current source or whatever it is seems a bit interresting.
Maybe a 6C19 or something would perform well with that kind of load, followed by a coupling cap and a transformer?
I have no plans for biulding that circuit as it is (a headphone amp),
but the current source or whatever it is seems a bit interresting.
Maybe a 6C19 or something would perform well with that kind of load, followed by a coupling cap and a transformer?
>>What is the difference between a CCS loaded triode stage and a mu-follower?<<
Not, a heck of a lot. In the circuit you provided, the FET CCS loads the parallel common cathode triodes. The triodes are cap. coupled to the FET's gate. The FET is doing double duty: CCS loading the triodes and serving as a voltage follower.
The advantages of a mu follower are high gain ("full" mu), LOW distortion and a low O/P impedance, not shabby at all.
A mu follower feeding a no standing DC current trafo is a good combination. Trafos have better bandwidth when driven by low impedance sources. As long as the coupling cap. between the O/P device and the trafo is large enough for good bass, the arrangement performs quite well.
Not, a heck of a lot. In the circuit you provided, the FET CCS loads the parallel common cathode triodes. The triodes are cap. coupled to the FET's gate. The FET is doing double duty: CCS loading the triodes and serving as a voltage follower.
The advantages of a mu follower are high gain ("full" mu), LOW distortion and a low O/P impedance, not shabby at all.
A mu follower feeding a no standing DC current trafo is a good combination. Trafos have better bandwidth when driven by low impedance sources. As long as the coupling cap. between the O/P device and the trafo is large enough for good bass, the arrangement performs quite well.
A good use for those big 12uF paper in oils I brought home a week ago, then😀
What is the function of the 2k resistor between source and plate?
In another circuit I´ve seen the resistor was absent.
Hi Fuling,
On Doede Douma’s site there is a good explanation of how a basic Mu stage works:
http://www.dddac.de/op01.htm
Happy reading 😉
On Doede Douma’s site there is a good explanation of how a basic Mu stage works:
http://www.dddac.de/op01.htm
Happy reading 😉
Hi,
Thanks to Doede to explain it in easy understandable words 🙂
IMHO you best bet is the battery powered FET cascode as a Mu follower Fuling, as Eli already pointed out. I am myself thinking to give it a try (if I find the time 🙁 ) but then use photovoltaic isolators like the PVI’s from IR for biasing the fets. This instead of using batteries and power the PVI's from the filament voltage. This will give me also a neat ability for delayed power on.
Cheers 😉
Thanks to Doede to explain it in easy understandable words 🙂
IMHO you best bet is the battery powered FET cascode as a Mu follower Fuling, as Eli already pointed out. I am myself thinking to give it a try (if I find the time 🙁 ) but then use photovoltaic isolators like the PVI’s from IR for biasing the fets. This instead of using batteries and power the PVI's from the filament voltage. This will give me also a neat ability for delayed power on.
Cheers 😉
I had an idea this morning:
This Mosfet/mufollower must be great for DC-coupled amps.
Since the Mosfet sets the idle voltage the output tube will have correct bias whatever happens to the driver tube.
This Mosfet/mufollower must be great for DC-coupled amps.
Since the Mosfet sets the idle voltage the output tube will have correct bias whatever happens to the driver tube.
Nope,
The mosfet set the current through the tube. At this current the grid voltage (set by the cathode resistor) set the anode voltage at that current.
How do you see that DC coupling Fuling? The DC anode voltage is still somewhere between 100 and 200 V depending on the triode used. The Mu stage output is some 10 volts above that if you don’t use an extra anode resistor.
Cheers 😉
The mosfet set the current through the tube. At this current the grid voltage (set by the cathode resistor) set the anode voltage at that current.
How do you see that DC coupling Fuling? The DC anode voltage is still somewhere between 100 and 200 V depending on the triode used. The Mu stage output is some 10 volts above that if you don’t use an extra anode resistor.
Cheers 😉
I was refering to this kind of circuit:
http://w1.223.telia.com/~u22306942/...FORSTARKARE.pdf
What I mean is that in this circuit the output voltage at zero signal must be set by the voltage divider connected to the gate of the mosfet.
The DC coupling I´m talking about would be to the next amplifier stage. ie the power tube.
Just like any DC coupled amp except that the mosfet circuit should provide some extra safety if the input tube goes south.
Are you with me?
http://w1.223.telia.com/~u22306942/...FORSTARKARE.pdf
What I mean is that in this circuit the output voltage at zero signal must be set by the voltage divider connected to the gate of the mosfet.
The DC coupling I´m talking about would be to the next amplifier stage. ie the power tube.
Just like any DC coupled amp except that the mosfet circuit should provide some extra safety if the input tube goes south.
Are you with me?
Yup, but my point is that it will stay at 150V even if the tube is pulled out of its socket (or any other fault condition), instead of hitting the rail voltage as it would if the plate load was a simple resistor.
I've been doing searches for the past hour on this same subject ... time to bring this dead thread back to life!
I was going to use some IXYS current regulators (aka Pete Millett) for my 6C45 plate load. My final design might use the IXYS part.
For some side experiments, I want to use a Aleph-type CCS.
Has this question been resolved?
I was going to use some IXYS current regulators (aka Pete Millett) for my 6C45 plate load. My final design might use the IXYS part.
For some side experiments, I want to use a Aleph-type CCS.
Has this question been resolved?
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