The Ranger, Viking, DX100 and the 32V3, etc. rigs are running Class C finals using plate modulation. They do not have an RF linear amplifier in them. Being a new comer you may not be familiar with the pros and cons of linear verses class C. I will try to stir up some interest here in maybe home brewing a larger rig but first you need to now a little about what you might build. Rigs such as Yasues, and Kenwoods, and other more modern SSB type, "Rice Box type" to coin a phrase, including the ones that have an AM mode, have small linear amplifiers built into the box. The modulation is done at a very low level (less than a watt) then the whole envelope (carrier plus sidebands in the case of AM mode) is amplified by the built in linear amplifiers to a 20 - 150 watt level depending on the mode and rig. These rigs may use a pair of 6146s for the linear amp outputs running in class AB1 or AB2. In the case of the Rangers and others the RF carrier is amplified using non linear class C circuits. We don't care if the amplifiers have a lot of RF distortion in the carrier because each stage is tuned with a LC circuit that removes the distortion and puts the output of each stage back to a pure sine wave at a single frequency of RF. Prior to tuning, these stages are rich in harmonic distortion because of the clipping of the current in the tube's class C biasing. They even tune some of the lower level stages outputs to the second harmonic so that, for example, the VFO may run on 1.9 MHZ and the output on 3.8 MHZ. At the last stage of class C amplification, the signal is tuned and matched to the antenna line. The carrier that is produce here is modulated by varying the plate supply voltage to the output stage (6146), with the audio wave form. This requires a high level audio amplifier (also built in the Ranger box). This audio amplifier is similar to any PA type amplifier with the exception that it's output XFMR is not designed to drive speakers but instead to match the impedance of the Class C final (6146), Ep/IP=Zmodulated. This is high level modulation. The Class C finals are good for CW, FM and AM high level modulation because of their high plate efficiency (70 - 80%). There or efficient because they don't spend much time between cutoff and saturation. Much like a switch that doesn't get hot as long as it is all the way on or off. But if you replace the switch with a normal variable resistor to try to actually control the level of output power then the resistor will produce a lot of heat. The power of the heat dissipation in the resistor plus the delivered output power is equal to the total input power. The linear amplifiers work similarly as for as efficiency is concerned. This does not mean that they are not a viable answer to you needs. The class C rigs of a few hundred watts require a large audio amplifier for the modulator. For instants, you might use your Ranger in CW mode to drive a pair of 812s in class C mode at a plate input power of 400 watts. In class C at this level, these will produce about 300 watts RF output and dissipate 100 watts in heat. You will need at least 200 watts of audio to modulate the 400 watt DC to the finals. This could be produce by a pair of 811As for modulators. You will need a modulation XFMR, filament XFMRS of finals and modulators. Enough plate voltage supply to power both modulator and final. You will also need the audio preamp stages for the modulator unless you plan on extracting the audio for the Ranger since it is not being used in the Ranger. Remember the Ranger in CW mode, is their to produce a carrier to drive the 812s and you only need 10 to 20 watts to do that so the audio circuitry in the Ranger is idle. I believe it has jumpers on the ACC plug that can be modified for this purpose. A linear on the other hand uses the AM output of the Ranger and requires on audio of its own. Simplicity trade off for plate efficiency. As to which ay is best for you depends, on what's available, your space, and what you want to learn.
Good Luck, John -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Paul Sokoloff Sent: Friday, December 19, 2003 9:30 PM To: [email protected] Subject: Re: [AMRadio] Looking for Linear Amp Hello again, I had no idea I was going to stir up such an interesting discussion. I was the person who originally posted this. After reading all of the replies and as a newcommer to this, I have one question. If one needs an 800 watt amplifier to run 100 watts AM, then how does a Viking with 3 small 6146s run 125 watts AM? I have a Johnson Ranger (45 watts with one 6146) which I wish to drive an amplifier for more output (maybe 125 to 150). Should I just get a viking 2 or an amplifier? Does anyone have an amp they are interested in selling? Thanks, Paul WA3GFZ _______________________________________________ AMRadio mailing list [email protected] http://mailman.qth.net/mailman/listinfo/amradio
