Re: Harmonic performance - SSB vs CW

Timothy Fidler
 

AJ Parent.. did you see my request for the  Msg on short form descrip of  work necessary to get 12 W out of Bit x 40 sent back to me .. Ie I had no record (silly me) as I was going to send it on. You may have missed that email from me in all the noise.

2. Resistors R97 and 98 near the IRFs : 47 ohm each. Has someone like you measured the VD across these at quiescent and back calculated the bias current.?? The word on the street - Hendricks kits build book (IRF510 x 2, 12W out and Plenty of drive too via BS170s ) as prev quoted - says it needs to be 50mA min per device. My suspicion is it is set  light on to ensure the Vreg does not give up.. perhaps at 35-40 mA. It might need to be higher than even 50 mA  for this SMPS Mosfet above 20 Mhz to stop clipping at change over during the RF cycle. If the bias is light on and can't be improved.. (obviously the light on bias regulator is an issue).. then the RD06HHF1## may be the only solution.  The Pinout does not work as a replacemen but the only pin that gives real trouble is the Source pin,  which would have to go directly  the the RF transformer winding in each case. This part sells for about $US  5 a pair on Ebay out of PRC. (and is not hugely popular so may well be not worth faking).  RF Parts in Calif has them for around $4.70 each.  NB There is nothing on the Mitsi datasheets re bias requirements for this in class B operation.

##  Caution this part may be very skittish in setting up the bias - and (2) it might also be over driven by the current driver set . Latter issue could be fixed with a through hole resistor wired Gate to drain. I note in passing that the IRFz24 which is known as  proven RF kludge mosfet (SMPS is the intended use) has 3x the transconductance of the IRF 510 so it may respond better to light-on  bias. The downside -   but also 3 x the nominal input capacitance so it is going to be harder to drive. So with a change out of driver transistors to say 2n2219A metal case and reduction in the emitter resistors in those four drivers " etc ". However it is cheap,  and it goes pin for pin with the incumbent. My minor and uneducated thoughts for this fine morning - Nz time.

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