I think that the 5596 is for the 28v system. After checking with Aircraft Spruce and the local FBO, both tell me there's not a quartz available for the 28V system. That can't be right. Even though Whelen has mislisted the 4509, they do show a Q5596 for the 152. I didn't expect ordering up to be this involved. I guess that's my next phone call.