Dang, those where the days... open chassis with upwards of 430VDC floating around; seems insane now, but back then it was SOP.
I remember the spark gap stuff my Uncle had. Rotary SG throwing around 1000V out in the open; Oh Yah! (Edit - No I'm not that old, but I saw old photos - but can you imagine how cool (and dangerous that was!)
I am currently playing with an Arduino solution to my dehumidifiers bad mother board. In development stage at this point.
So far I have the Arduino reading a DHT11 and displaying the results. The rest shouldn't be too hard.
, Ron WB9YZU