Hi all. First post here. Looking for identification on these. They say SDA 1 on back, I never see just 1’s online, always 1A,1B etc. I was told they are A1’s. I’ve had them since 1988. Are these the first SDA’s? I changed out the SL1000’s to SL2000’s about 20 yrs ago. Would RD0194 be the correct tweeter replacement? Any info or history on these would be much appreciated. Thanks.