I know for lots of us a DN2540 is the go to device but I found something else that may be useful. There is a new line of high voltage, high power jfets that are interesting. If you look at this $6 190w 650v device you will see there are no curves suplied below a few amps and that's a shame. I was playing around with one of these and found that down at about -8v it makes a darn good ccs. I was actualy concerned with using it as a ccs between 10 and 30v and found I got about ! amp using a 8 ohm source resistor with 12v on the drain and it only went up to about 1.1 A when I went to 36v on the drain. Then for fun I went to a 110 ohm source resistor and 36v on the drain this gave me about 72ma and then I jumped up to 300v on the drain and I then just measured 76 ma. These devices do varry a little with there turn on voltage so your results will varry some. https://www.mouser.com/datasheet/2/827/DS_UJ3N065080K3S-1530401.pdf
I've often wondered how these would do. Anyone measured the performance?
My next amp will have an LTP front end using something like a 12BY7A, and I was going to use something like a BF256B for a really simple CCS. Doesn't need to take a lot of voltage in this case, and it simulated quite well. Of course, we've all simulated things only to realize they're a complete dog (and I don't mean a border collie) in real life .
But these power JFETs are interesting for a whole number of reasons...
My next amp will have an LTP front end using something like a 12BY7A, and I was going to use something like a BF256B for a really simple CCS. Doesn't need to take a lot of voltage in this case, and it simulated quite well. Of course, we've all simulated things only to realize they're a complete dog (and I don't mean a border collie) in real life .
But these power JFETs are interesting for a whole number of reasons...
I thought about using one of those Silicon Carbide JFETs instead of the plate choke that is in an SE Parafeed amp.
That would eliminate the limitations of the choke's inductance at low frequencies, and the chokes distributed capacitance at high frequencies.
The main problem is two-fold:
1. Need 2x the B+ voltage
Which causes . . .
2. Power inefficiency.
That would eliminate the limitations of the choke's inductance at low frequencies, and the chokes distributed capacitance at high frequencies.
The main problem is two-fold:
1. Need 2x the B+ voltage
Which causes . . .
2. Power inefficiency.
I know this might be a bit backwards, but what are your guy's thoughts about putting this in series with a DN2540?
The power Jfet ontop since it can deal with high voltage and has better thermal characteristics, and a DN2540 on bottom since its performance is well known and it wouldn't be too much of an unknown variable.
Im in the middle of what 6a3 summer is suggesting and I am looking at using a CCS in a single ended parafeed amp. Sadly the IXYS chips will heat up really fast if you pass a few watts through them. But these Jfets have much better thermal characteristics. If they could work in this application, that would solve so many problems.
The power Jfet ontop since it can deal with high voltage and has better thermal characteristics, and a DN2540 on bottom since its performance is well known and it wouldn't be too much of an unknown variable.
Im in the middle of what 6a3 summer is suggesting and I am looking at using a CCS in a single ended parafeed amp. Sadly the IXYS chips will heat up really fast if you pass a few watts through them. But these Jfets have much better thermal characteristics. If they could work in this application, that would solve so many problems.
I have a pair of mono-blocks with four KT-120s in PPP configured as a LTP with a current sink "tail". It's sinking 300mA with almost zero tempco (+-0.25mA). Consists of a high current, high voltage Fairchild N-channel power MOSFET and a Fairchild KA-431 (low tempco TL-431). The KA-431 is biased with LM-334/DN2540 cascode providing ~2mA. Had an output tube arc, three times, and amp and current source survived and continued to play music.
I have cascoded DN2540 with higher-voltage, higher-powered IXYS devices with good results. The increased capacitances caused me to have to use more compensation, so I was able to get 300kHz out of the circuit whereas I was able to get 400kHz with a 10M90s as top device.
