Re: sbitx v3 circuit and performance details
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I am curious to see what you get too. I am curious because you are using Vishay devices and I am using Bojack devices. Mine are also not matched at all, I just grabbed two out of the bag and soldered them into place. I have a 4 amp current limiting power supply I built back in trade school that I used to setup?my radio. That was how I stopped the avalanche current problem?on mine.?
Gyula, I think?there was a miscommunication between us earlier. I didn't mean for that to sound like I needed 50 watts. I meant that was the test output into the dummy load to stress test the mosfets. I am sorry I misled you to think otherwise.
David WK4DS On Sun, Jan 19, 2025 at 7:42?AM Gordon Gibby KX4Z via <docvacuumtubes= [email protected]> wrote:
The MOUSER order for?
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942-IRF520NPBF 12 12 0 0.592 7.10
?MFG Part No: IRF520NPBF
?Infineon Technologies MOSFT 100V 9.7A 2
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IRF520's from "infineon" arrived a few days ago.? ?They are marked "IR"? (International Rectifier) on the body.? ?I managed to get them installed over Aluminum nitride insulators and got the idling current set for about 0.25-0.30 A earlier today.
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1.? Getting the tab to easily go FLAT on the heatsink proved to be more difficult than I had expected.? ?I think I didn't allow enough "slack" in the device leads when I soldered it and that caused it to be pushed into an odd angle that meant a lot of force had to be supplied by the "bar" to hold them down.? ?I didn't like that and slept on it to think it through better.
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2.? I ended up re-heating the solder connections while the devices were held down by the "bar" to allow some movement of the leads? ?I think that helped.? ?I should have used a tiny bit more lead length.? ?
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3.? (I'm still using the staked-in female screw jacks -- I haven't drilled through to add a back nut.? ?If they were to fail, I think I woud do that next time)
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4.? Starting from FULL COUNTER CLOCKWISE, and using a small "wall wart" 12-VDC supply, I was able to set the idling current.? ?I try to always do this with a WALL WART with limited current capacity since I don't have a laboratory current limited power supply.? These are only few dollars and are WELL WORTH HAVING for non-destructive re-setup of one of these radios.? ? (For me, I also have a polarity protection circuit inline -- these are valuable radios and I hate the thought of destroying one with reverse polary.? ?Once I get the polar protection inserted, it never comes out, STAYS with the radio from then on.? ?)
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5.? Based on the rotation of the potentiometer, a slightly higher (more positive) bias gate voltage was needed on the IRF520 than with the previous IRFZ24N.? ? That's just differences in the devices.? ??
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6.? I have Ashhars recommended bi-directional TVS diodes (with miniscule 3pf capacitance) in place.? ?Soldering those with my tools was quite a feat!!? ? They have astonishingly low junction capacitance compared to what I see for typical axial leaded devices.? ?
Later today I should be able to start making some power measurements and resetting the hardware coefficients for the various bands.? ? I bet I'll see more power on the higher frequencies with the significantly lower junction capacitances.? ??
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Gordon KX4Z
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WK4DS