Hi Larry, That circuit you describe---i.e. using four 6KD6 sweep tubes in parallel---appears in the 1969 ARRL HANDBOOK... You'll note the use of individal pots accompanying each tube to "equalize" the resting currents. "I think" those tubes that I smoked were not all in vain, after all...I merely "reversed engineered" the cause of my (then) woes! ~73~ Eddy VE3CUI - VE3XZ