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In Reply to: RE: Schottky diodes posted by lovetube on June 03, 2015 at 18:15:23
What filaments? You'd want a very different Schottky diode to heat a 45 than, say, a 2A3.
Follow Ups:
"What filaments? You'd want a very different Schottky diode to heat a 45 than, say, a 2A3"
Oh goodness, I've heard that schottky's were susceptible to blowing at turn on/in-rush. I just thought as long as the amperage was high and the voltage not to high about 600v then I'd be good to go.
Have gone and used Cree C3D04060 For my 6SN7 bridge here?
I'd like some suggestions for my 300B filaments...
The C3D04060 has a pretty high voltage drop, which is a tradeoff to get the higher operating voltage. This is not a particularly good selection for a low voltage heater supply.
300B's don't need a ton of current, 1N5820 ought to do fine.
Diode selection is a balance between forward voltage drop, device dissipation (load current * forward voltage at that current), and supply voltage vs. load voltage.
If you use the C3D04060 to heat your 300B's, you'll see a little over 1V of drop across each diode at 1.25A, so we'll say 1.375W of dissipation. The datasheet doesn't specify the thermal resistance to ambient, but it may be somewhere around 60-70C/W, so you may see a 90 degree temperature rise in the diode, which will reduce its lifetime and burn the board that it's attached to (unless you heatsink it).
If you go to a diode that drops less than 0.5V, you end up with much less heat dissipated, as well as more available voltage.
Turn-on will rarely damage these parts, as they are almost always cool at turn-on, and the stress of initially heating a filament isn't going to raise the device temperature quickly enough to matter.
If you are modifying an amplifier that is a commercial design, I would suggest that you are doing a lot more harm than good.
Gathered enough from your recommendation IN type diode, have gone with Vishay Schottky VT5202. Thanks for your help
http://www.mouser.com/Search/ProductDetail.aspx?R=VT5202-M3%2f4Wvirtualkey61350000virtualkey78-VT5202-M3%2f4W
What will you do if the Schottky bridge makes too much voltage?
"What will you do if the Schottky bridge makes too much voltage?"
Increase the single 1R resistor after the diode bridge.
Conversely, if there was too low a voltage would it be possible to drop the value of the the two before the bridge say to 0.1R? What is the purpose of these two and how low could one safely go?
If you are modifying an amplifier that is a commercial design, I would suggest that you are doing a lot more harm than good.
It all started with replacing the ordinary lytics for black gates and film caps, and progressed from Std's to here. I now have the caps around the 300B's BG NH in Super-E config and VK's with the 5687's.
Tants on the main board and 6SN7 board takmans grid. Still have the same iron, but these are pretty much what Audio Note would have done if I had shipped it (tants) as for super-e config and VK's I've prolly pushed it a little further than I could have paid for. And it has been a ton of fun.
The diode bridges were just standard KBU types, I am surprised to see that they don't seem to put schottky's in the level five gear.
If the amp is designed for KBU's, use KBU's.
"If the amp is designed for KBU's, use KBU's."Seems, that I'm starting to do a full circle back to where I started.
I did contact Peter Qvortrup of Audio Note initially with my thoughts as to changing from KBU's to Schottky's and I got a favorable response without any particulars just saying to keep the voltage requirements reasonable (not too high)
I have these neat little boards lined up from china and this is where I would really appreciate some help, I guess schottky's with a similar spec to the KBU4K for the 6SN7's, And KBU6J for the 300b's.
I don't know why AN would specify these, but to my thinking wise to not stray too far from these requirements, but hey I'm clueless here?Schottky's that I can solder directly into this board?
The C3D4060 I have learned I didn't make a particularly good choice, they do however fit right into this board and heatsink...
Edits: 06/07/15 06/07/15
well.
just like a few that good for filament and heater DC and that should be good .
I wouldn't use DC on the 45 or the 2A3 . so may be list a good dioes that is good for DC heater ,
LT
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