I have a pair of 4cx250b/4x150a tubes as modulators for my 813 AM transmitter. Great tubes, you can go from 1000 volts on the plate to 2000 volts in AB1 without bias or screen voltage changes. 900 watts of audio out, the same for CW I suppose. That's at 2000 volts 500ma. They take zero driving power in AB1, just voltage, so a typical tuned grid input would work.
The downside of the 4cx250b type tubes is you need a blower and the special sockets, and regulated screen voltage for low distortion on voice. Not sure if you need to regulate the voltage for CW... Many tubes take low driving power if you do the tuned grid input. Its another thing to tune, but not really hard to do, a tapped coil on a ceramic form with a link at the bottom, or separate coils of B+W coil stock switched in gets the drive for a pair of 813's down to about 15 watts for over 600 watts out in class C. My pair of 813's is not neutralized and seems to have no problems working from 1.8 to 30 mc. I set it up so it can be class c or AB2, all parameters are metered and adjustable. For those who like to look at pictures.. http://wa5bxo.shacknet.nu/N2DTS/ Picture 61, the 813 rig is the right cabinet. Brett N2DTS > [warning thread drift] > > The Linear Amp kits seem to need a fair amount of drive. I've been > idly thinking about a linear that would allow me to drive it with > my barefoot K2 and get 600-800 watts out for CW. > > I've been told that such things were "common" in the 70s. One > description > I was given is > > two stages, with a pair of 6CL6 pentodes in class A passive grids, > driving a pair of surplus 4CX250Bs in AB1,a very common design. > 0.1W in gives 650W out. > > which sort of means something to me, but will certainly start many > evenings of study. > > If this was "common", it seems that there should be articles. > I haven't > had much luck finding one (there's an article from 1959 that uses > a single 4CX250B). So, how about it, you guys who were there then? :-) > > 73 de chris K6DBG > _______________________________________________ > Elecraft mailing list > Post to: Elecraft@mailman.qth.net > You must be a subscriber to post to the list. > Subscriber Info (Addr. Change, sub, unsub etc.): > http://mailman.qth.net/mailman/listinfo/elecraft > > Help: http://mailman.qth.net/subscribers.htm > Elecraft web page: http://www.elecraft.com > _______________________________________________ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
