Jeff, Remove the plate voltage. Apply grid drive. Dip the plate tuning. Measure the output signal of the rf deck (I used the receiver S meter).
Adjust the neut caps evenly for minimum output on s meter. Neutralizing problems can be from... Filament leads not bypassed, Ground wire from tuning cap open or too long, Neutralizing caps too close to coils, Coupling between grid and plate coils excessive, Shielding too close to plate circuit coils, Parasitic oscillations My push pull 811/812 rig neutralized very nicely, but was very sensitive in the adjustments. I used two vacuum variable caps, something like 6 to 30 pf 10,000 volts (came out of vhf transmitters) and it was very critical in adjustment. Its impossible to adjust it without rf on the grids, no problem reaching in the and adjusting it, I put regular knobs on the vacuum variable shafts and just twist them while watching the s meter on the receiver. Un neutralized, meter is pegged, neutralized has it about 3 db. Changing between 811 and 812 tubes requires re neutralization, and even between different sets of the same tubes needs a touch up... its also possible to sort of neutralize my deck by having one cap set for much more capacitance than the other, but it does odd things when set that way. Its very important to balance each tube, and that way, the output signal drops VERY low on the S meter... Brett N2DTS > > > I've been trying to get my old 250TH rig back on the air. > for the most part, I've been rather successful. but, I've > run into a kink... I can't seem to neutralize the final. > > > The final uses Cross Neutralization. > The final "C" section is a B&W Butterfly tuning capacitor > Neutralizing caps are on the end of it. > > Thoughts? > > Regards, > -Jeff > > _______________________________________________ > AMRadio mailing list > [email protected] > http://mailman.qth.net/mailman/listinfo/amradio
