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IXYS 10M45 CCS IC question

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Quick (and hopefully easy to answer) questions :

How many volts at minimum does this chip need to drop to work satisdfactorily? I'll have about 200 V B+ available and want to drive a 12AT7 . Will this suffice .

Likewise, will this CCS happily regulate at 2 - 5 mA or is it more stable at higher currents (I'd have to look at a different tube)?

Thanks
 
I have found they are happiest with 20V minimum headroom. That includes the signal voltage, not just operating point.

The datasheet seems to imply operation as low as 1-2 mA, but I haven't used them this low. I think, based on the Idss rating, the DN2540 is able to run higher currents in cascode, so possibly the IXYS is better at low currents ?
 
If current was truly held constant, needs only a resistor under the cathode.
I suppose if you are driving a low enough impedance, cathode current might
not correllate exactly the same as the plate....

Either way (LED or Resistor), I'd bypass with a good cap if the voltage is be
held constant.
 
The IXYS data sheet for this part is pretty brief.  They list an Id of 2-100mA, and no minimum voltage (max voltage 450).  I'm using them at 9mA - 68V, and they're perfectly stable.  Pete Millet tested on a 6SN7 section at 5mA (no voltage given, but the plate curves indicate 80-85V), and reported better technical performance and sound than with a 100K resistive load.  In practice, you'll want to have the swing of your plate plus maybe twenty volts across the thing, I would think, and if you're dissipating over a watt or so in it, slide a heatsink onto it.  I'm burning 0.7W in mine, and they hardly get warmer than my hand.

A caution; there's some example-to-example variation, about 10% or so, in Id/Rg-k, so you need to put a little pot in there as well. I use a 250Ω metal film and a 100Ω 12-turn little pot.  It's fun to adjust your OP with a screwdriver and hear what you can hear; very instructive.

Aloha,

Poinz
 
I forgot to mention. This project is a 12AT7->RC->12B4A->old 5K/8ohm console transformer . Should be good for a watt or so.

I'm using a single red LED on the tail of the 12AT7 and am starting off with plate resistors. Once everything is working, I'm going to substitute them with my IXYS CCS and compare the sound.

Future plans include a "powerdrive" circuit on the 12B4A grids. Just using boring resistors for now.
 
The 12B4A can be turned near fully on with only +0V on the grid.
I'm not sure how much grid conduction you are fighting? Probably
only capacitance... If you superdive with a MOSFET for no reason,
might be worse capacitance than your 12B4A grid... 5 picoFarads
times Mu of 6.5, your superdrive gate would have to be 32pF or
less to beat it.

Your 12AT7's plate resistance is 10K-15K pending on voltage...
Roll off (-3db) into your 12B4A's grid*mu at only 331,741Hz!...
So unless you ARE forward conducting, I'm not sure the point.

You might try a cathode follower. 6AU6 Pentodes I got lots of
spares. Would do just fine in that application. Or use your 12AT
as the follower. I got more 6DJ8's than you could shake a stick
at (Used perfectly good HP/Amperex, and Tektronix/Telefunken),
you could have up front... I may have a 12AU6 if you want 12V.

I also have an excess of 6U8A's if you can figure out what they
might be good for.... Triode + Beam Pentode in one Noval...

And EF95's go figure...
 
Poindexter said:
A caution; there's some example-to-example variation, about 10% or so, in Id/Rg-k, so you need to put a little pot in there as well. I use a 250Ω metal film and a 100Ω 12-turn little pot.  It's fun to adjust your OP with a screwdriver and hear what you can hear; very instructive.

Aloha,

Poinz [/B]


Hi, is the pot placed in series with the resistor that sets the CCS's current? So you are using the pot to match plate current between channels?

Thanks for bringing it down a level for me :D

Dave
 
Yes, that's exactly right.  You series the fixed resistor and the pot to get exactly the current draw that you want.  If 10% is close enough, and you don't have two channels to match, you don't need to do it.  You can read the current from any resistance in the power supply current path, even the fixed resistor in the resistor-pot series.  If you have a bigger resistor, you'll get a more precise reading.

My application is in the 'tail' of a singly-driven diff-amp.  This is a pair of 6GK5s, each loaded by a 43K resistive load, and this load is where I take the reading.  A 190 volt drop across this resistance indicates a 4.4mA current draw.  There are two of these, so (approximately, within tube matching tolerance) 8.8mA.  If this were the 249Ω fixed resistor in the control circuit, I would be looking for a 2.2V reading.

I didn't have to drop it a level for you; you're right on the cam.

Aloha,

Poinz
 
CCS - 7A4 to 300B

Hi,

I bought a few of IXYS10M45 from Digikey and have them implemented in my 300B monos. The IC is used as the plate load for the 7A4 driver. The 7A4 employs RC in the cathode and it takes approx 5mA plate current.

I am rather impressed with the sound after changing from 27K resistor load to CCS. I read another article saying that the high frequency isn't that good with CCS because the high grid capacitance at the 300B. My plan is to change the 7A4 to 7N7 so that I can add a buffer stage between the CCS driveer and the 300B.

According to the datasheet, this IC works starting from 10Vdc to 450Vdc. Therefore, it is best for use as plate load.


Johnny
 
I haven't measured the frequency response with use of CCS. According to the information from http://www.pmillett.com/current_source.htm, the difference in -3dB point at high frequency between resistor load and CCS is 79kHz to 53kHz.

CCS is just little weaker at extreme high frequency. In this case, it is better for me to live with the pure CCS drive to the 300B.

May be I can use paralleled 7N7 with CCS plate load to drive the 300B which should get more better high frequency response. The CCS chip is mounted to the chassis plate which forms excellent heatsink. I could run it at around 15mA total.


Johnny
 
Well, I got the amp working with load resistors on the 12AT7. Need to get the CCS in (luckily, I still have a fair bit of space left in the chassis).

Regardless, this amp is something special, .. though just 1.5 WPC running into some old 5K console OPTs and off-the-shelf components, and adhering to the rats-net school of amp. wiring :). Makes one reallywonder about the law of diminishing returns.

Just a wee bit of hum through around 100dB speakers at less than 1 meter, so I'm not going to worry about it. Power supply is minimal (5uF film - 10H - 47uF electrolytic). Haven't bothered with decoupling driver and power stages.

I'll post schematics and better pics in a separate thread when done.
 

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What kind of power does the current adjustment potentiometer between the G and K terminals on the IXYS CS need to be able handle?

I'm currently building the CCS . I have a couple of tiny 1K clarostat trim pots . Will they suffice? I don't expect to pass more than 10mA (probably more like 3 - 5mA) through the CCS .

Also, I'm assuming I use just 2 of the pot terminals (the wiper and one end) and ignore the other.

Thanks and apologies for the solid state ignorance.
 
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