Hi Bret: Many of us have played with neg cycle loading to find the same thing that you have found. You would need a low pass filter after the limiting circuit but these things make the audio have resonate peaks and limited freq response. (poor sounding) If you have good freq response in the lows then your audio will probably be lopsided anyway, especially if you talk close to the mic.
SEE - http://www.qsl.net/wa5bxo/asyam/aam3.html Good luck, John, WA5BXO -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Brett Gazdzinski Sent: Sunday, April 04, 2004 10:51 PM To: amradio@mailman.qth.net Subject: [AMRadio] RE: negative cycle loading Hello all AM,ers. I was running the new 4d32 rf deck on the air over the weekend, and it works very well. I 'stole' the 811a modulator from the 812a rig to modulate the 4d32 rig till I get the kt90 mod deck built. After many and various tests of different voltage and currents on the plates and screens, etc, it seems to like running at 1100 volts and 300ma, for about 220 watts out, although I can get 300 watts out. It modulates well, up to 900 watts pep. But my negative cycle loading setup seems to introduce spurs out the sides when it comes into play. I looked at it on the spectrum analyzer. I use the 3 diode, resistor, and separate power supply that sets the negative percentage (using a variac). I once talked with someone on the air about this circuit, and they told me it had a design flaw, and needed something, another diode, resistor, or something, but I cant remember what they said, or who said it. I use the 1 amp 14,000 volt diode bricks in the circuit, and maybe something to do with switching speeds, bias, or something, but when I invoke the circuit, I get big spurs out the sides, out to 30kc each side 40 db down. The mod monitor says the modulation is getting limited to 90% or whatever I set it to, but running it is even worse than over modulating. I use this circuit in a number of rigs with the same results. The audio is clean, and I even added some resistors to the plates of the 811a mod tubes, grids are swamped, adjusting the various voltages and drives on the 4d32 rig has zero effect on the spurs. Sure would like to get the circuit to work well, as I can run the audio up much more and load the negative spikes. I don't want to run into it heavy, just trim some peaks off the negative side. Thanks for any info, Brett N2DTS _______________________________________________ AMRadio mailing list AMRadio@mailman.qth.net http://mailman.qth.net/mailman/listinfo/amradio