For years I wanted speakers like Dad’s JBL’s. One day I inherited them. They are C38 cabinets with D131 woofers (flatbacks), 075 tweeters, and N2400 crossovers. They are all original and sound fine. Of course they never had much bass. When they came here they were paired with a Velodyne ULD-12 sub. It’s a good combination.

I wondered how old they really are. The flat back D131’s are 1954 or earlier. I think the 075 tweeters were introduced in 1955. I definitely remember the cabinets from 1955. My sister thinks earlier.

I had some crossover issues and the left tweeter would go off and on every time Jet, a sable Burmese cat, walked behind the cabinet. It turned out to be a loose screw inside the crossover. Of course once that was fixed the right tweeter had the same problem. That’s how I discovered the D131’s are flatbacks. I shined a flashlight through the opening and they did not look like the JBL’s I’d seen. The Lansing Heritage website has been very helpful in helping me sort out my questions.

Long before Dad’s JBL’s came home to me, a neighbor had JBL L65 Jubals. They were great, but the tweeter, a 077, was a complete mystery. I had no idea what a ring radiator is, how it works, or that the 077’s cousin was sitting inside Dad’s old speaker cabinets.

With respect to ring radiators I really appreciate the thread here:

Great information… I know that 075/2402 diaphragms are thicker and heavier than 077/2405 diaphragms. There was also mention that the 076/2403 was in between. Recently I found this:

The third page notes the D16R2405 s the correct diaphragm for the 2404, 2405, and variants. The fourth page notes the D8R075 as the “closest substitute available" for 075/2402 variants. The D8R076 is for the 2403.

Just to wrap things up, when I was a kid, our property was next to Roy Marquardt’s estate. I played a lot with his son Bruce. We knew Roy was a whiz with ramjets, but I never knew about his association, albeit briefly, with JBL. Small world…

Paul Haussler