Date: Wed, 3 May 1995 17:49:08 -0500 From: "Barry L. Ornitz" To: Multiple recipients of list Subject: RE: Tune for maximum output or plate dip? On Wed, 3 May 1995, John Mallick wrote: > Has it ever been resolved about "tuning for maximum output" vs. "tune > for maximum output, then DIP the plate as the final maneuver"? The > latter is what I have been using on my Drake T4XC, and it seems to > work well. > > 73, John WA1HNL If the rig is properly neutralized, AND operating into the same impedance as it was when it was neutralized, AND the tubes are matched, plate current dip will exactly coincide with maximum output. For a reasonably low VSWR, the two should be pretty close. If they are drastically different, check your neutralization and tube matching. I usually ran at plate dip, but I guess the correct way would be to use the setting that provides for the highest plate efficiency. Calculate the power input using plate voltage and current, and measure the power output with a directional wattmeter (the difference between forward and reflected power). The difference between the two, ignoring tank circuit losses is plate dissipation. The ratio of the two is the efficiency. I have never tried this, but it should be an interesting experiment to see which technique results in higher efficiency within the constraints of a maximum plate dissipation. [BTW, don't be surprised if the dissipation is in excess of the published sweep tube ratings. This was common with SSB rigs. You could get away with it with the low duty cycle and the low cost of tubes. Swans were especially bad about squeezing every last drop of power out of sweep tubes.] 73, Barry WA4VZQ ornitz@emn.com ------------------------------------------------------------------------- From N6EV: Note: When peaking output power instead of dipping the plate, you may be sensing harmonic/spurious outputs combined with the fundamental. Peaking the output may not be peaking the fundamental output frequency. Spurious/ harmonic content of the output increase out of tank resonance. I've always trusted dipping the plate over peaking the output because of this. 73 Paul N6EV