I recently picked up a pair of NOS 23834 diaphragms meant for 288 drivers (late production version with the recessed phenolic ring and spade connectors) with the intention of swapping out the Symbiotik drivers in the 291A drivers. However, in the process of swapping and installing the new diaphragms, I found that the alignment pins on the 291A drivers are slightly too wide to fit the replacement diaphragms and thus does not allow it to seat properly. Images attached with fitment of both original Symbiotik and NOS 288 (23834) as well as closeup of the 291A alignment pin.
I was under the impression that these diaphragms were interchangeable across the 288/291/299 family of drivers but it seems not? I'm not sure if it is because 291 is an early series and the 23834 is a late production or some other reason. I have heard rumors of a conversion kit that exists but have not come across any reliable information. I had thought the kit was just replacement leads to adapt spade connectors but is there a possibility that a gasket is also needed?
Is there a way to properly fit these diaphragms to my 291A or am I SOL? Any thoughts/advice/experience would be greatly appreciated!
(If anyone has a pair of earlier production 288 diaphragms to compare/trade or even a pair of 288G that they would be interested in trading for the 291A, let me know!)
I was under the impression that these diaphragms were interchangeable across the 288/291/299 family of drivers but it seems not? I'm not sure if it is because 291 is an early series and the 23834 is a late production or some other reason. I have heard rumors of a conversion kit that exists but have not come across any reliable information. I had thought the kit was just replacement leads to adapt spade connectors but is there a possibility that a gasket is also needed?
Is there a way to properly fit these diaphragms to my 291A or am I SOL? Any thoughts/advice/experience would be greatly appreciated!
(If anyone has a pair of earlier production 288 diaphragms to compare/trade or even a pair of 288G that they would be interested in trading for the 291A, let me know!)
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Great Plains Audio/Acoustics used the 23834 number. Their 23824 is rated for 40 watts, the original 288 diaphragm only 15.
Great Plains was formed in 1988 after the closing of the Altec Lansing factory in Oklahoma City.
This is an interesting statement:
I don't know how they make "adjustable dowel pins"..
The 290 used a phenolic diaphragm, the later 291 the Symbiotik, both of which had far more power handling than the original 288 aluminum surround diaphragm.
I'm not an Altec history expert, but it would make sense that the higher powered drivers would use a larger pin size to prevent replacing a 120watt phenolic or 50watt Mylar surround Symbiotik diaphragm with the 15 watt all aluminum 288 diaphragm.
If that replacement was done in a PA system designed for high power, the 288 diaphragm would likely fail in a short period of time.
Assuming the pin size is the only difference, the 23834 diaphragms alignment pin holes could be drilled (adjusted?) to fit the larger pins, and the usual cleaning and alignment procedure performed prior to putting the back cover back in place.
Art
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Great Plains Audio used to have a diaphragm cross-reference on their site, but I just looked at the Great Plains Acoustics site and the cross-reference is not there. That said, you can probably get in touch with their experts and ask your question there. https://greatplainsacoustics.com/
