8950's cost is steep. 6KD6 or 6LB6 best.The Maco 200 does not really have enough
iron
for 8950,6lx6 or 6LF6. But......Replace the "Parasitic Suppressors" connected to the
Anode of tube. US made carbon resistors radically change value with age in that spot.
Check the RF choke on the Input. ( L4 ) If its toasted. duh replace. Check on each final
tube "R7" connected to G1 control grid. Again carbon resistors. The finals from the
above schematic are in "AB2".
Grid current flows. The finals require a - bias voltage to prevent "runaway" of the tubes.
Carbon resistors ohm's increase drastically with age. This would result in the - negative
voltage being even less than it is supposed to be. Translation. The plate current of the
tube is not limited. Hence runaway. Blue I'm blue is good when U modulate. Not Red.
Lastly how many Watts are U pushing into this aged Maco ?
Could be AC getting into the plate of the tubes ? Take a few pics. top & bottom ?
Without a tuned input filter & a Pi-L tank circuit + an over modulated CB. U bet. I.M.D. all over the Band !!!!
Maybe a hundred watts on the frequency the CB is on. The rest from 2 meters to 80. A chunk of
splatter on 10 meters Ha Ha !
Best PuppetMaster
