IXCP10M45S

[mr2racer]

Hey Anyone,

If I use an IXCP10M45S as a constant current source for a 6N6P do I still need a plate resistor? Or a cathode resistor?

Thanks, Kevin

[Fenris]

I'm assuming you are talking about a standard grounded cathode gain stage.
As a plate (anode) load, no you don't need a resistor. You could use one to reduce the power dissipated by the 10M45 since a constant current with a constant resistance produces a constant voltage drop. Just make sure that the voltage drop by the resistor isn't so much that it interferes with the voltage swing of the tube.
You will need a cathode resistor to set the bias point. You can also use a LED, diodes, or a zener diode if you wish.

[jazbo8]

Always do a seach before you start a new thread!
Decade-old thread: Ixys IXCP10M45s IC

[mr2racer]

I did do a search but must have used the wrong terms as nothing came up.

[GoatGuy]

Maybe someone knows the answer to this…

But doesn't using any type of constant-current source maximize the effect of Miller capacitance between the plate and grid producing the lowest pole of (and least desirable, I'd guess) high-frequency roll-off?

If I recall accurately, the cascode topology, where the "amplifying tube" is fed by a constant voltage anode load almost completely counteracts Miller capacitance by limiting the voltage swing of the anode, which in turn can't feed its inverted "signal" back to grid thru grid-anode Miller capacitance.

And ordinary resistor load is intermediate: it modulates the anode with the inverted, amplified signal, far more than the cascode constant-voltage load, and less than any of the various constant-current loads. (Think … 10M45 CCS or 250 H choke load, or interstage transformer load or even gyrator loads), so the effect of Miller capacitance anode-grid feedback is modestly reduced. Indeed: it is reduced directly in relationship to how much gain the stage is designed to have.

Just wondering, is all.

And wondering … if the optimal design “solution” (as long as one is contemplating employing a chip-of-silicon) mightn't just be a MOSFET+resistor cascode anode load. Almost completely bypassing the Miller capacitance hi-frequency roll-off effect. You know?

Just saying,
GoatGuy

[6A3sUMMER]

GoatGuy,

Good to hear from you again. Good points.

Cascode operation significantly reduces the miller effect of the bottom stage. But, if you get the same gain out of the plate of the top stage versus a non cascode stage, the current that the plate has to supply for slewing the grid / plate capacitance is the same (well actually C x gain versus C x (gain +1)). True, the top grid is tied to AC ground, so it is not influenced. But . . . the plate impedance of the top tube in a cascode stage is very high impedance, versus a simple common cathode stage.

So now the high impedance cascode plate has to drive the next stage's grid resistor, and any grid to cathode capacitance, and any grid to screen capacitance if there is a screen, and any miller capacitance if there is no screen.

What is the distributed capacitance of that 250H plate choke load? That might have more effect than the miller effect.

And I used to use interstage transformers, but did not like the square wave look, nor the phase and frequency response (I never felt I could "afford" the really good interstage transformers, so did not even have the chance to use and test them.

But for me, I do like the 900V version of the IXYS CCS in the triode plate load. My tweeters and my ears do not seem to know the difference (do not work well above ~ 20kHz for the tweeters, and about 13kHz for the [one] ear. I do use a lower resistance input potentiometer than many do, to partially swamp out the effect of the miller capacitance. And I do use real resistor plate loads sometimes too, instead of the IXYS CCS.

Not all lunches are free.

[GoatGuy]

Hmmm… didn't think of it from that angle. Thanks 6A3sUMMER. GoatGuy

[mr2racer]

I'm planning to use the CCS as a plate load for each tube in a simple two stage line preamp. Set at 10ma with a 10 ma bias on the girds. Tubes are 6N6P.

[6A3sUMMER]

mr2racer,

10mA bias on the girds (grids)?
You are not going to put current into the grids are you?

How about a schematic?