Hi, i‘m repairing old Radian 835 CDs, however i‘m struggling a bit with the phase plug.
It has come loose on both of my units and i‘m a bit hesitant to glue them back in. Dry fitting them they seem to sit way too low, it‘s certainly a lot more distance to the diaphragm than what‘s written in the service instructions (.5mm). Also when the glue fell off the plastic stubs on the plug i had the impression that it added some height. Unfortunalety i didn‘t keep the glue residude to measure the thickness. Also inspecting the edges where the plastic dome should go into the metal structure there‘s probably half a mm or more missing. I know it from other manufacturers that they note down the height of the assembly and diaphragm to match the distance with mylar shims, but the service bulletin just instructs to use whatever shims are included with replacement diaphragms (mine came without any).
Could it therefore be, that there is extra tolerance in the motor assembly, to be aligned and fillen with glue at the factory? Do you have any idea how i could do this myself with diy tools? I‘m already afraid to build some kind of a test device with a dial indicator or similar 🥲
Any help is much appreciated!
It has come loose on both of my units and i‘m a bit hesitant to glue them back in. Dry fitting them they seem to sit way too low, it‘s certainly a lot more distance to the diaphragm than what‘s written in the service instructions (.5mm). Also when the glue fell off the plastic stubs on the plug i had the impression that it added some height. Unfortunalety i didn‘t keep the glue residude to measure the thickness. Also inspecting the edges where the plastic dome should go into the metal structure there‘s probably half a mm or more missing. I know it from other manufacturers that they note down the height of the assembly and diaphragm to match the distance with mylar shims, but the service bulletin just instructs to use whatever shims are included with replacement diaphragms (mine came without any).
Could it therefore be, that there is extra tolerance in the motor assembly, to be aligned and fillen with glue at the factory? Do you have any idea how i could do this myself with diy tools? I‘m already afraid to build some kind of a test device with a dial indicator or similar 🥲
Any help is much appreciated!
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It does appear that Radian is relying on the glue to "take up the slack" in the phase plug alignment.
I suspect they insert shims under the plastic portion of the phase plug in the glue process to lift it to the proper height.
Putting shims made of thin strips of plastic near the three glue "feet" you could get the angle to match the steel and plastic portions to that of the diaphragm at that point.
After you are satisfied with the height, apply the glue and reinsert the phase plug.
That said, worth checking in with Radian to get their suggestion.
Good luck!
I suspect they insert shims under the plastic portion of the phase plug in the glue process to lift it to the proper height.
Putting shims made of thin strips of plastic near the three glue "feet" you could get the angle to match the steel and plastic portions to that of the diaphragm at that point.
After you are satisfied with the height, apply the glue and reinsert the phase plug.
That said, worth checking in with Radian to get their suggestion.
Good luck!
I'd attach an old diaphragm with a thin coating of white wood glue to the phase plug, let it dry, then apply epoxy to the tabs of the phase plug and insert the diaphragm/phase plug setup back into the VC gap to cure. When its glued up, peel away the old diaphragm and you'll end up with a perfectly spaced and conforming phase plug.
Thanks for the answers! Eyeballing it is then 🥲
I did contact Radian, but they didn‘t/couldn‘t provide any help, not even the type of glue.
In the meantime i also came up with an idea: i applied layers of pvc tape until there was an ever so slight touch. With a datasheet thickness of .13mm and 6 layers i should need to lift the plug around (6*0.13mm) - 0.50mm = 0.28mm. Of course i have to check that with digital calipers, but that should be the ballpark. Or do i have a mistake in my assumption?
@profiguy:
clever idea! But wouldn‘t this leave me with no or uncontrolled clearance at all?
Also included a pic of the old diaphragm where the loose phase plug must have „polished“ the aluminium haha. I didn‘t run it that way, bought the cabinets as is for a restauration project.
I did contact Radian, but they didn‘t/couldn‘t provide any help, not even the type of glue.
In the meantime i also came up with an idea: i applied layers of pvc tape until there was an ever so slight touch. With a datasheet thickness of .13mm and 6 layers i should need to lift the plug around (6*0.13mm) - 0.50mm = 0.28mm. Of course i have to check that with digital calipers, but that should be the ballpark. Or do i have a mistake in my assumption?
@profiguy:
clever idea! But wouldn‘t this leave me with no or uncontrolled clearance at all?
Also included a pic of the old diaphragm where the loose phase plug must have „polished“ the aluminium haha. I didn‘t run it that way, bought the cabinets as is for a restauration project.
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Yep, all my Altec diaphragms have/had annular phase plug 'skid' marks sooner or later and since I use(d) their loading cap, its center channel indent on the backside, though never noticed any loss of performance till the VC pulled loose, though the OEM glue 'shadow' was sufficient to superglue them back in place with no obvious loss of performance.
Wonder if that level of quality is available today.........
Wonder if that level of quality is available today.........
If a .28mm lift make it look like the right side of this picture, sounds right to me 😉
Phase plug segments should make surface with a smooth, constant curvature, so use whatever spacers are needed to achiev that. I second @weltersys on that.