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Old 5th December 2012, 10:33 AM   #11
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One point with these IXYS devices is to take care handling them - make sure your hands are grounded when you touch the pins.
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Old 6th December 2012, 12:31 AM   #12
50AE is offline 50AE  Bulgaria
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Although the devices alone work great as a single CCS, I just can't do the cascoded CCS, the current keeps stuck at 1mA . Could it be something to do with the gate stopper resistors?
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Old 6th December 2012, 10:59 AM   #13
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I had trouble with a cascode myself - not sure why. Maybe it needs greater headroom?
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Old 6th December 2012, 11:01 AM   #14
SY is offline SY  United States
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That would be my guess. I haven't used that device, just the DN2540. But if the transistors aren't blown, then compliance voltage may be the answer as to why. Unfortunately, the datasheet I have doesn't really show the curves...
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Old 6th December 2012, 12:07 PM   #15
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Thanks for that, SY. I didn't have that much headroom so used a single device.
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Old 6th December 2012, 12:55 PM   #16
Magz is online now Magz  United States
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I have no problem with 10M45S cascodes. I make sure I have lots of headroom, though, on the order of 90-100V.

By the way, I'm using the "mu output" of the CCS in my 26 preamp and it sounds excellent, in addition to giving an output impedance of ~1500ohms. I don't hear any degradation versus the plate output - if anything it sounds better. The lower impedance allows me to run the tubes directly into the autoformer volume controls and avoid a separate output transformer. Combined with lossy parafeed the low end extension is -3dB at 4-5Hz.
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Old 6th December 2012, 01:10 PM   #17
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Datasheet for the Supertex part indicates capacitance drops significantly once you get about 20-25V of headroom. In my uses in about 5 different amps, they run just fine with 20V. I would not suggest running them below 10 if you want decent performance. The lower the capacitance, the higher the output impedance at high frequencies.
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Old 6th December 2012, 06:17 PM   #18
50AE is offline 50AE  Bulgaria
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B+ is 300V and anode voltage is 150-160V. So 140V left for the 10m45s not enough? The current is 30mA

Last edited by 50AE; 6th December 2012 at 06:19 PM.
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