This is the grand Hallicrafters SX-71. A five band receiver covering 560 kHz to 56 MHz. Mode of reception include AM/NBFM/CW. Riders schematic 21-21 to 21-30. This unit is in for possible restoration.
This is a second SX-71. The challenge with this radio was finding and repairing two cracked IF slugs. The slugs were discovered during the alignment. It was a lucky break that the slugs were repairable. They are made of Unobtainium.
Once this radio was fully aligned its sensitivity climbed tremendously. It must have been a pretty deaf radio for its previous owner. Most of the alignment adjustments were curiously far from the proper alignment. A few possibilities occur to me.
Unfortunately, the audio output transformer primary opened up soon after this unit was returned to the owner. A direct replacement seems not to be available. However Peter Dahl Company A subsidiary of Harbach Electronics, LLC, can custom make a new transformer. The cost is in the area of $170 - $190. If you want original functionality (500 ohm speaker impedance) then this is the way to go.
For this unit the owner chose a universal Single Ended output transformer. The 500 ohms speaker impedance is the only feature compromised with this Hammond HX-125CSE Transformer. The cost of this transformer is about 33% of a custom wound transformer.
To match a 500 (600) ohm speaker with a speaker matching transformer. Built by Hammond in response to requests from the "Collins Collectors Association" for a matching audio transformer for older equipment with 600 Ohm audio output.
In its day, owning a Hallicrafters SX-71 must have made many a Ham envious as for I find it both accurate and sensitive. Today it is a handsome radio that is a pleasure to "scan the bands" with.
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