> 2SC2782 is rated at 80W min each at 175 MHz so getting 150W > from two on 1.8 MHz should be peanuts; the main reason why > they are restricted to 110W in K3 is linearity (across bands) > + component ratings. At higher power, the efficiency can be > higher and thus K3 may actually run cooler!
Don't try it ... with 12W max available from the LPA, the pair of 2SC2782 are already working very near maximum gain at 100 W output when the other losses are considered. The 2SC2782 shows 6.4 dB gain 1t 12.5V ... (12W drive, 80W Out). Derating the gross output by 1 dB for circuit losses in the LPF and T/R switch and 1 dB for linearity purposes, the net output is right at the K3's 110 W maximum output. If you really must have 200/250 W output, build an external amplifier using two MRF-150 instead of the four used in Motorola Engineering Bulletin 103 by Helge Granberg. See: http://www.ab4oj.com/dl/eb104.pdf In addition to the added power output, operating with a 48V power supply provides improved IMD (-33 dB @ 150 W) and gain (>20 dB). 73, ... Joe, W4TV > -----Original Message----- > From: elecraft-boun...@mailman.qth.net > [mailto:elecraft-boun...@mailman.qth.net] On Behalf Of Ignacy > Sent: Friday, December 11, 2009 4:06 PM > To: elecraft@mailman.qth.net > Subject: Re: [Elecraft] [K3] 150 watt "boots" for 160m > > > > Those who believe in authority and that God punishes > tinkerers, PLEASE SKIP this message. > > 2SC2782 is rated at 80W min each at 175 MHz so getting 150W > from two on 1.8 MHz should be peanuts; the main reason why > they are restricted to 110W in K3 is linearity (across bands) > + component ratings. At higher power, the efficiency can be > higher and thus K3 may actually run cooler! > > So how to get 150W out of K3? > > 1. ALC would not let it. It needs to be fooled, e.g., by > changing a divider in the SWR unit to indicate 100W when it is 150W. > > 2. At 150W the output impedance would not be 50 Ohm; it would > be 35-40 Ohm with extra impedance added by LPF, which are > designed for 50 Ohm. You need a manual tuner that you will > tune for max power, not min SWR. If higher SWR causes power > fold up, the SWR circuit needs to fooled again. > > 3. The radio would take more amps, say 30A, and the fuse may > go out. If so, change the fuse or reduce the power so that > the fuse is not tripping. > > Is it worth it, I am not sure. In contests, the extra power > may make a real difference. > > Would Wayne and Eric approve? Never officially! > Would K3 be ruined? I doubt it. > Would I do it if I wanted to win a 160m contest in LP > category and had no other alternatives? Perhaps on CW but > never on SSB due to high IMD. > > > Corresponding story > Many years ago a power supply for IC-735 broke and the spare > one was for 5A max. Tuned for min SWR the power was 5 W. > Tuning for max power out generated 25W. > Later, I tried the same trick with IC-7000. It was 5 W no > matter what the tuning because of strong power folding under > high SWR. Not sure what K3 would do. But there is a > possibility that one can get 10-20W more just by tuning for > max power out. > > Ignacy > > > > Julius Fazekas n2wn wrote: > > > > Wondering if anyone has a suggestion of a solid state amp > or "pushing" > > the K3 PA to obtain 150 watts out on 160m? > > > > A kit or HB would be fine... > > > > 73, > > Julius > > n2wn > > > > -- > View this message in context: > http://n2.nabble.com/150-watt-boots-for-160m-tp4151943p4153762.html > Sent from the [K3] mailing list archive at Nabble.com. > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:Elecraft@mailman.qth.net > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
