Dennis, > I've had good results with the "three diode" circuit too. Earliest > reference to the scheme I can find is in QST, October 1956 > using 866 rectifiers. > Covered again in ER #3, July 1989, this time with solid state > diodes.
I did not say I had good luck with the circuit, although it looks like it works on the scope, and on the mod monitor, it results in a very wide signal. Not much point in running it if you go 50Kc wide... > Don't believe the type of diodes used would have any > significant effect on > this. Splatter is generated in the PA tank circuit when > plate voltage is > suddenly cut off on the audio negative half cycle. Same > splatter would be > produced if the PA was being fed straight off the secondary > of the mod transformer. The 3 diode circuit is supposed to prevent the plate voltage from going to zero. I use variacs on the power supply so I can set the point at which the circuit starts working, and no matter if I set it to 95, 90, or 85% I get splatter if the audio would exceed 100% negative, so the circuit seems to do no good. It LOOKS like it works, I get current in the negative cycle loading circuit, mod monitor shows the limiting working, scope looks ok, the signal just gets REAL wide, no matter what rig I run. Everyone would assume it works, I did, till I got reports I was real wide and dug out the spectrum analyzer... Perhaps the very high frequency stuff gets past the circuit? I should run some tests... Brett N2DTS > > Dennis D. W7QHO > Glendale, CA
