AC/DC Circuitry for Receivers & Transmitters

[Rod Fitz-Randolph]

Michael Hopkins wrote:

>The Mighty Midget RX uses a pair of 6U8s in a fitting tribute to Thoreau's
>"Simplify, Simplify" admoniton, but the author did not go far enough.  He did
>not need the transformer.
>
>   After reading C.F. Rockey in Sicience and Mechanics' Radio-TV Experimenter
>#576 for Spring 1961 (a Dayton find) at page 149, I saw the promised land.
>
>   That pair of 6U8s draw 450mA or, said another way, have an equivilent
>resistence of about 14 ohms or 28 ohms the pair and it takes a total of 266
>Ohms to drop 120 volts down to ground.  If we just had something that drew
>about 240 Ohms to put in series, we would not need the filament transformer.
>What?  Rockey used a lightbulb.  Figure it out.  Put a 60W in series, perhaps
>the one in your bench light, with the tube heaters and you have light plus
>heater voltage.  Rockey built his short wave set into a little student cabinet
>with a bookshelf and place for the lamp too.
>
>  But what about the plate voltage?  You knew before you asked -- take it
>right off the line a la an AC/DC rig of yesterday or today's TV set.  It is
>wise to rig a neon bulb up to say when you have the plug in backward, but the
>caterwalling of counsels for the the plaintiff notwithstanding, there is
>nothing wrong with an AC/DC setup.  Frank Jones used them all the time and
>died of old age.  If the 100 or so you get isn't enough, put in a voltage
>doubler.
>
>  Had old Henry David Thoreau listened to a radio, you can bet he would not
>have bought a second transformer -- the big one on the pole would have suited
>him.
_________________________________________________________________________
Well put!  I use AC direct for many of my home projects.  I have built a
transmitter on a plastic chassis and the highest exposed voltage to anyone
using it is the 12 VDC across the key terminals!  Safe as a church!

Dunno why the Wussies are so afraid of the type of circuit that supplied
voltage and current to an estimated 100 million household radios in the
50s and 60s.

A little forethought and common sense can make the AC/DC current source for
home projects as safe as any other mode.

Rod, N5HV
w5hvv at aeneas.net

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