[Boatanchors] SB-220 in AM service

[RAY FRIESS]

That's one good thing about the old Palomar amps ... like the 300.   6 sweep tubes (two driving 4) and
you can get almost 500 watts out AM with only 40 or 50 watts drive.
A little "redoing" to prevent spurious emissions and it's a great sounding half KW.
 
 



> Date: Wed, 12 Mar 2008 14:09:00 -0800> From: jwiley at alaska.net> To: rbethman at comcast.net> Subject: Re: [Boatanchors] SB-220 in AM service> CC: boatanchors at mailman.qth.net; ke7kk at earthlink.net> > I use an old Drake L-4B in AM service, and have used it for more than 20 > years, with no failures - and the same set of tubes. I usually set it > for about 350 watts unmodulated carrier output (the max allowable is > 375 watts, which which with modulation equals 1500 watts PEP). I tend > to be long winded, but the L-4B is a continuous duty rated amp, and was > built properly. It has a pair of 3-500Z tubes, a squirrel cage blower, > chimneys on the tubes, tube sockets in a pressurized plenum, plus a > separate power supply that can really take some guff. > > > The SB-220 should be OK at 250 watts or so out, as long as you limit > continuous talk time to 10 minutes or less , with no more than a 50% > overall duty cycle. Keep your eye (or nose?) on the transformer - if it > starts to smell hot, back off on the talk time. For a test, I ran the > L-4B on 20 meters at 1000 watts output for a hour into a dummy load - > other than the power supply starting to smell a bit warm, and the tubes > getting sort of orange, no problems.> > > Before the rules for AM changed, I used to run it at about 400 watts > carrier output, mostly on 10 meters AM, also with no problems. However, > I did manage to unsolder the connections inside an external low-pass > filter doing that. > > > Good luck. Maybe I will hear you on the band once I get my 10-meter > antenna back up. > > > - Jim, KL7CC> > > > >>> Greetings Anchor People> >>>> >>> The Heath SB-220 in the shack is seldom used and I would like to use > >>> it in> >>> AM linear mode with low power exciters such as the Heath DX-60, Knight> >>> T-60, HT-32 / 37, HX-500, WRL DSB-100 etc. As its rated for 1KW CW > >>> RTTY> >>> (10 Min max) I thought that 250W input on AM should not stress the > >>> power> >>> supply or tubes, in the low power position (graphite tubes) At 60%> >>> efficiency that should be approx. 150W rf output. Any thoughts from > >>> others> >>> who have used the Amp on AM ? Thanks for your input Bill KE7KK SD> > Bob Bethman/NØDGN/BC-610/Northern Radio SP-600 Manassas, VA - > > MultiBand Dipoles> >> > _______________________________________________> >> >> _______________________________________________