Hallicrafters SX-99 Mark 1D Shortwave Receiver Punch List (Crystals, Trimmers, Sensitivity) and etc.

After a quick look at some WWI helmets, the third Hallicrafters SX-99 restoration project has developed a punch list of items during use since completion last September. An intermittent hum at the 6SC7 audio amplifier has been nagging me, and the radio seems to be not sensitive, especially Band 3 and 4. The selectivity crystal was found way off at 457 kHz and so I explored ways to bring the crystal resonance closer to 455 kHz. But still the sensitivity was too low, until I found the problem.