I wrote up a blurb about the design of the Heathkit AJ-1510A and unlike most Heathkit products, there are a number of design errors. There is a zipped file which is the attachment in the
http://www.diyaudio.com/forums/analogue-source/195272-heathkit-aj-1510-tuner-help.html
thread but since I can't find a way to attach a file in this forum, it is best to go there and unzip the file. When you buy this tuner, BE SURE TO GET THE MANUAL. I cannot emphasize that enough. Even though the schematic is on the net, the board layout diagrams are a must. And $550 is insane. I got mine for CDN$150 which happens to be a good price - they normally go for $150 in US dollars.