View Full Version : JBL 075 "Railroad Transducer" tweeters

04-29-2009, 09:10 PM
I have a pair if these (green horns) and I've heard that 077's were used
also, depending on pattern desired.

Question is...did these have special diaphrams, and which one was it?.
One is red-sealed, other one has been open. These are in great condition.
Is there a good article on these here?.

04-30-2009, 08:21 AM
I bought a pair of these pea green RR bullet noses drivers several months back from Fleebay. When I opened the units up the diaphrams were crinkled and the units were packed with sand, dirt, hair, and other naturally recurring junk from years of outside exposure to the elements.

I assume the RR diaphrams are no different from the ones used in HiFi applications but I could be wrong.

Anyway, since I was not sure about their history, I decided to replace the diaphrams with new OEM units and to have the alnico magnets recharged to factory specs.

I sent the cores and new frams to Bill from Great Plains Audio who has a large magnitizer. Apparently, this machinery is NOT very common and only a few places can do this service.

If you change the diaphrams yourself care should be used to NOT twist the fram when installing the nose cone. The nose cone should be held secure when tightening the small nose bolt from the rear.

I removed the pea green paint from the nose using a wire wheel but a scotchbrand scrubber works too. I spray painted the horns black.

There are a few posts here discussing these drivers.

04-30-2009, 08:31 AM
use the word "tideland" in the search function for the threads.

The diaphrams *are* unique and NLA.

05-03-2009, 10:28 AM
Back in my QA days, we used to test the GRS/Tideland drivers at only 17,500 Hz, as that was the specific frequency they were used at, in traffic sensing/signalling applications. Don't think I'd use them in a Hi-Fi application. I do not know the difference in Diaphragm construction though. Maybe Harvey could possibly expound on it for you.

05-26-2009, 11:55 AM
We had a few of these green monsters installed in several traffic locations around the White Plains NY malls, apparently, for the assistance of the blind folks.

Anyway, their sensativity is so freq'n high you could hear them from several blocks away. After years of service, they finally replaced them with something cheap and less vocal.

The pair I purchased from Fleabay and rebuilt using new factory frams and a motor re-charge are now working well in a hi-fi application.

My JBL reconer who inspected the units while they were apart, claims their design and construction is no different from other 075/077 drivers.