Thanks so much for taking the time to remind me about all this stuff!!! When I was 25 I worked on a Gates 50B that was as old as I was. I mostly just monitored voltages and looked for trouble.
I was facsinated back then as I find myself being now while I foray into the world of AM again. I spent too much time in Broadcast as a studio tech. Cheers, Alan VY2WU Quoting Donald Chester <[EMAIL PROTECTED]>: > > > > >From: Alan Beck <[EMAIL PROTECTED]> > > >I would like to use a cheap am with my DX-60. > > > >An SB-200-230 seems to be a Class B amp. There for it only conducts on the > >positive going cycle. I don't mean to sound silly, but someone told me I > >could run this in SSB Mode using AM input from my DX-60, I run 100 Watts > >carrier for 400 Watts peak, now that makes sense. > > > >What does not make sense is how do I get the other side of the wave > >form???? The Tank??? I guess the tank. > > > > The linear will work on AM as long as you don't exceed the peak power output > > rating. Exceeding the peak output rating will cause the signal to flat-top, > > distort and splatter. > > Another thing to watch for is the plate dissipation of the tubes. If I > recall correctly, the SB-200 series uses a pair of 3-500Z tubes in the > final. That means you have 1000 watts of plate dissipation available. > Running AM linear @ 100% modulation will give carrier output efficiency of > about 30%. So you could run maximum 1500 watts DC input to those tubes, > with 500 watts carrier output, and 1000 watts dissipated by the tubes. With > > modulation, the tubes will actually cool down slightly, since the DC input > will not vary, but the amplifier will deliver sideband power in addition to > carrier power output. So some of the input power will be converted to rf in > > the sidebands instead of heat in the tube plates. > > But you also have to be careful with the power supply. AM runs at 100% duty > > cycle, so the power supply in the amplifier may not be rated to run 1500 > watts continuous duty. After a few minutes, the power transformer may > overheat. In that case you will have to run it at reduced power. But be > careful that the plate efficiency does not exceed about 33%. If you run it > at too high plate efficiency, it will not leave you enough headroom to > accomodate the positive peaks, and flat-topping/distortion/splatter will > result. > > Don't worry about the missing half of the rf cycle. It works with AM > exactly the same way as it does with SSB. Since the amplifier is single > ended and not pushpull, the missing half of the rf cycle is filled in by the > > "flywheel effect" of the rf tank circuit. > > In summary, with class-B linear AM operation, the final will run about 33% > carrier efficiency. The peak efficiency on modulation peaks will be about > double that, 67%. Two-thirds of the DC input to the final will be > dissipated as heat in the plates of the tubes under carrier-only, no > modulation conditions. That means the carrier output will be one half the > plate dissipation of the tubes. The peak power output should be about 4 > times the resting carrier output at 100% modulation, if flat-topping is to > be avoided. > > Linear amplifier AM operation dates back to the very earliest days of radio. > > The earliest high power broadcast stations used it. It was used for years > > before anyone figured out how to run audio amplifiers in class-B. Before > then, the only kind of high level plate modulation that was used employed > class A audio amplifiers, usually the "Heising" circuit but sometimes series > > modulation was used. Both those systems ran at lower ovarall efficiency > than linear rf amplification. Therefore, AM linears were used long before > high level plate modulation for high powered AM transmitters. > _____________________________________________________________ > > This message was typed using the DVORAK keyboard layout. Try it - you'll > like it. > http://www.mwbrooks.com/dvorak/ > http://gigliwood.com/abcd/ > > > ______________________________________________________________ > AMRadio mailing list > Home: http://mailman.qth.net/mailman/listinfo/amradio > Help: http://mailman.qth.net/mmfaq.html > Post: mailto:[email protected] > AMfone Website: http://www.amfone.net > AM List Admin: Brian Sherrod/w5ami, Paul Courson/wa3vjb >
