V2 circuitry with gate inductors and resistors/? ?blown IRVZ24n, both replaced with IRF520
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OK,? I don't have the patience of Ashhar, but I have managed to set up my original V2 radio now with IRF520 MOSFETS from "Infineon" (marked International Rectifier) so that it basically achieves a linear near-maximum output power at 100% drive.? I have an old radio shack swr meter that has a voltage-derived power meter that is pretty "close" after calibration except apparenlty at 40 meters where it is a bit optimistic.? Using that meter I developed coefficients that appeared workable (though perhaps not absolute maximum) and then checked with a siglent digital scope and 10X probe with on-screen measurement of RMS voltage on a Heathkit ancient 50 ohm cantenna and converted to power.? ?The sBitx internal reading (which I have separately calibrated long ago) is similar
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IRF520? Infineon? ?biased for about 0.3Amp total idling current
3pf TVS diodes on gates instead of the previous huge zeners (which Ashhar says don't stop the problems)
MODE = CW? ?Power measured by Siglent scope and mathematically voltage -> 50 ohm power
Frequency? ? 100% drive output power? ? hw_settings.ini? ? Comment
3.5010? ? ? ? ? ? ? ?32W? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? .0037? ? ? ? ? ? ?Gets a little less power than on 40, similar setting to IRFZ24N
? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? my earlier notes suggest I got a little more power than this, with the IRFZ24N's
? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? and gate zeners, so the IRF520 may be a little inferior here.
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7.010? ? ? ? ? ? ? ? ? 33.3? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?.0028? ? ?
10.1? ? ? ? ? ? ? ? ? ? 22.6W? ? ? ? ? ? ? ? ? ? ? ? ? ? ? .0028? ? my notes indicate I was in the range of 21W with IRVZ24N & gate-zeners
14.01? ? ? ? ? ? ? ? ? 16W? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?.0032? ? my notes here on IRFZ24N don't make sense
18.1? ? ? ? ? ? ? ? ? ? ?9.33? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?.0061? ? ? ? ? ? ?? the gate circuit reactance issue here?
? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?notes indicate I got 11-12W with IRVZ24N's
21.01? ? ? ? ? ? ? ? ? 16.6? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? .0054? ?notes indicate I could only get 15W with IRFZ24N & gate-zeners
24.9? ? ? ? ? ? ? ? ? ? ?12.3? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?.0063? ?notes indicate I could only get 10W with IRFZ24N & gate-zeners
? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?likely due to their huge capacitance
28.0? ? ? ? ? ? ? ? ? ? ?11.52W? ? ? ? ? ? ? ? ? ? ? ? ? ? .0063? ?notes indicate I could only get 8W with IRFZ24N & gate-zeners
? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? likely due to their huge capacitance
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From Ashhar's earlier data, these are no particularly huge improvement or decline from what he is able to get with IRF510's, so his choices make excellent sense from a manufacturers' reliability standpoint.
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Hope this information is useful to tinkerers who consider the higher Drain-Source IRF520 with the oriiginal IRFZ24N circuitry of the V2 version
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Gordon Kx4z
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From MY standpoint I like this because I do a lot of NVIS and other work on lower bands and prefer to be able to drive a linear amplifier with this rig and/or use digital waveforms on WINLINK etc.? ?With 32-odd watts I can derate a bit? and still get good power with likely good linearity.? ?Ashhar's choices are better researched and possibly even better in ways I don't even understand.
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Because this is now so "new" since installing those MOSFETs I did not dare to do any "brick on key-down" tests.? ? The IRF520 is said to have a slightly lower junction-to-tab thermal resistance, and the aluminum nitride is a significant improvement over mica but my physical installation may not be as good as theirs, and CONTACT is the most important item other than the insulator.
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I'm just pleased as punch to have a working V2 version again -- and several bags of good MOSFETS now available and the itty bitty TVS diodes.? ?I had bought a SECOND unit (secondhand also) and will need to tear into it to change the insulators etc.? ?In all the time I've had this sBitx this is the FIRST TIME I've ever blown a final.? ?I had a uBitx V3 and never blew those either, I think.? ?Going to 100V D-source mosfets may be a real winner and for the older V2 driver, using the TVS diodes also likely a winner.??
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For these test's I reset the T/R switching delays to intermediate values (not right in front of me) about 2/3 of what Ashhar had.??
The CW? is set to do 20 checks/sec on the key.? ?A straight key was used to key the unit for power testing.? ??
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