[Boatanchors] YTuned / Not-Tuned Input---Final PA

[Ed Swynar]

Hi Gang,

Anyone who has ever built a MOPA rig for the low bands, & then found that the final RF amplifier stage is more T.P.T.G. oscillator than amplifier---as I discovered to my chagrin with my 6AG7 driver / 2E26 RF amplifier---pull the L/C network right out of the grid stage of the final, & go it alone with the 2.5 mh RF choke in the plate lead of the driver...

Your input will be untuned by doing this, but on the low bands you should have more than enough drive, dependent upon tubes used. I'd be hesitant about trying this on, say, 10- or 15-meters, but it seems to work well enough for me on 160-, 80-, and 40-meters. Just watch for "double-dipping" when tuning the final tank---if your VFO output is untuned, you may well be peaking on a harmonically-related band!

A lesson learned: when building that first-time GB rig, always remember that LESS IS MORE. I started out with an ultra compact set-up here, using a 6DT6 buffer between the outboard 12AU7A VFO & 6AG7 driver, regulated voltage on the 6DT6, selectable cathode / grid block keying, tuned drive, etc. etc. What a mistake! I needlessly complicated things with such circuit sophistication, & the thing never worked 100%...now I've pulled the 6DT6, VR tube, made it cathode keying only, & extracted the L/C after the driver---and the result...? It now works like it's supposed to!

...AND I have a couple of less controls to fiddle with, & more room under the chassis, to boot.

~73!~ Eddy VE3CUI - VE3XZ