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Hallicrafters S-40A

Press the PLAY button to hear the description in morse code.

The 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.

Chassis and Case Cosmetic Restoration

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.

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Electronic Restoration

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 IF.

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 .

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The Final Product

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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