Re: BITX40 output power at 36 volts to the IRF510 #bitx40help #bitx40

Timothy Fidler
 

On Sat, Aug 4, 2018 at 04:30 PM, Timothy Fidler wrote:
Not only will the capacitor let go but the IRF will open up and spray silicon and electron smoke about.  THe WA2EBY amp runs 40W max flat out at 24 DC supply and Kossor admits in his  notes (part 2 of that article ) that the IRFs will probably only last a couple of hundred hrs given the hammering they are getting.  Now you are trying to make one off IRF 510 in class A at say 35 perc eff outwork TWO IRFs in class B with a lot of professional design work behind them... it is not going to happen. The silicon temperature will exceed 150 degrees if you were at that power level. The IRF has a  therm resist of 3.5 W/K Junt to case and regardless of what heatsink you bolt on  (CW mica washer of  thermal resistance of ...4.7 W/C all up). you will still have that as your major thermal resistance. see https://www.fairchildsemi.com/application-notes/AN/AN-4166.pdf   If you want to  mod the design to give near 15W all out with a fair bit of rework pse contact me via PM but you will have allow say USD 25 for bits and pieces to do it (but it would be fun) . One concern that I have is that Farhan is publishing Q4 as a 2n2219A  metal case npn but what shows on the photos is a T39 case RF driver.. you take my point. If the physical entity and the schematic do not agree it is pretty involved to re-engineer a physical board. I suspect that the driver is a 2N3866.  Please inspect and advise before you contact me.  TEF 

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