EMRFD Message Archive 4554

Message	Date	From	Subject
4554	2010-04-23 07:58:37	Tim	Critique this class C 80M MJE181 12W push-pull amp
You guys might remember me goofing off with transformers and a simple push-pull DC-DC converter last week. Well, I took it a step closer to RF Design and designed a simple MJE181 12W push-pull amp using LTSpice. If you go to "Photos", "N3QE Spice", and look at my 80M MJE181 12W push-pull amp simulation you'll see the latest result. Intended to be class C. It takes 10mW in, has a 2N3904 push pull stage stolen from EMRFD fig 12.73 (Sleeping bag radio), followed by a MJE181 (super cheap 10W-class plastic audio transistor) push pull stage. With 12V Vcc I get a little more than 12W RF out with about 19W in for a net efficiency of about 63%. This direct link to the picture may or may not work: http://groups.yahoo.com/group/emrfd/photos/album/1536449451/pic/390687970/view?picmode=original&mode=tn&order=ordinal&start=1&dir=asc My gut feeling is that I might be able to get a little more efficiency in class C but maybe this isn't too bad. Any critique of the design?
4556	2010-04-23 10:31:44	Tim	Re: Critique this class C 80M MJE181 12W push-pull amp
As an aside, playing around with 40M, 30M, and 20M versions of this amp in LTSPICE, simply scaling L's and C's in the output bandpass, it looks like it'll work well on 40M too. By 20M the power out is really dropping as we are getting a lot closer to the 50MHz fT of the MJE181... but it still seems useful with a little tweaking of the MJE181 base drive, I get the impressi
4557	2010-04-23 11:23:45	ajparent1	Re: Critique this class C 80M MJE181 12W push-pull amp
Problem: The images are 1inch mono color squares and unviewable. Likely good. One detail with a 50mhz FT the best you can hope for is maybe 40M, reason is the gain will be so low above that the you waste a lot power as drive. However there are other audio transistors in that power class with FTs above 100mhz an oldie was 2SC1226A with an FT of 150mhz but there are plenty of newer ones. There are plenty of CB finals (12W 60V Ft 150mhz or higher) that are ideal for 160 through 10M. They are designed to be class C, cheap, common and rugged enough for bad SWR abuses with AM modulati