[R-390] Ballast Tubes

[Jim Brannigan]

My first radio was a Hallicrafters SX-77A AC/DC SW receiver.  I was
enthralled with short wave listening
One day it died......  as a 12 year old kid I had no idea how to fix it and
no test equipment.....I was devastated...
The next family gathering I grabbed a non-ham EE uncle and pleaded with him
to fix the radio....
He figured out that the portion of the ballast tube that controlled the
filaments was blown.  From the schematic he calculated the current
requirements of the tube filaments and from there the value of the necessary
dropping resistor.
(This took several hours and it wasn't 'till years later that I figured out
what he was doing)
We went to the local "radio store" (remember them), and purchased the
correct value resistor.  Since I did not have a soldering iron, the pigtails
were simply twisted around the correct pins of the ballast tube.
That was in 1962.  The resistor is still there and it still works........

Jim


> One modification that has not been mentioned as part of this thread on
> ballast tubes is probably the oldest of the batch. Grab a plug that
> looks like a tube base and wire a resistor to it. The value needs to be
> right to get the filaments to run right but that's about all there is
> to it. It pulls no more power than the ballast tube and it's a totally
> reversible mod. When the bottom drops out of the ballast tube market
> you can plug one of those two dollar ballast tubes in there and nobody
> will ever know what you did.