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Press the PLAY button to hear the description in morse code.
Hallicrafters S-40A is a general coverage receiver that tunes from 540KHz to
40MHz in four bands. It has nine tubes including a 5Y3 rectifier. It is a post
WWII product but is similar to the prewar S20.
The front panel
paint of this radio was in good condition but was very dirty. I did, however,
touch up the edges and around some of the controls by carefully wiping on some
black enamel with a small piece of cloth. I added coats until it looked
'right'. The lettering was acceptable after a good cleaning with mineral
spirits. Both of the dial covers were badly warped so they were replaced with
plastic from the craft store. I painted the red tuning stripe on the new dial
covers using masking tape to delineate a narrow line in the proper position. I
stripped the case of all paint that had been applied on top of the factory
paint and sanded it smooth. I then primed the case with auto body primer and
sanded again. A quality black enamel was applied as a final coat.
All of the
capacitors were replaced including the electrolytics in the power supply. I
also made several modifications to this radio. I realize that a 'real' restorer
would keep everything original, but it was my intention to use this radio and I
wanted it to be as good as possible within bounds.
The 6SA7 mixer tube was replaced with a 6SB7-Y. The radio was silent above 18
MHz with the 6SA7 installed. With the 6SB7-Y the CB band was there where before
there was nothing. No modifications are required to the radio to use a 6SB7-Y.
It has twice the conversion efficiency of a 6SA7.
The 6SG7 RF amplifier tube was replaced with a 6AC7. This required some changes
to the screen supply and bias resistor. The 6SG7 was moved to the first IF
amplifier socket and replaced the 6SK7. The cathode resistor was changed and a
decoupling resistor and capacitor was added to the screen supply for the first
A zener diode from the BFO plate to ground was added to regulate the B+ which
improves frequency stability with line voltage and signal level changes.
The headphone connection was changed to use modern low impedance headphones.
A 'magic eye' tuning indicator was added using a schematic found on the web. A 1629, which requires twelve volts for the filament was
used. A voltage doubler provides 12 volts from the 6-volt filament supply.
Schematics that include the changes I made are here and here .
This radio is at
least as sensitive as my SX111 but the selectivity is not nearly as good. The
selectivity circuits just are not in this radio. With a short ten foot inside
antenna it is super sensitive. Surprisingly it does not overload on strong
signals as I thought it might do with the 6AC7 RF stage. After a half hour warm-up,
the frequency stability is pretty darn good. SSB reception is great. Since
there is no product detector it is necessary to crank the volume control full
on and control the gain with the sensitivity control. I listened to a ham in
Tennessee the other night on 80 meters working a contest using SSB and could
hear most of the folks he did and some he didn't. I received some in Arizona,
Kansas, Maryland and Ontario with the 10 foot inside antenna. I wonder what it
would do in a quiet location with a good antenna?
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