• The move to the new server is done. There are some software and database maintenance updates in process. This has us passing the hat around to help out. We appreciate any donations. Seriously, even a dollar helps. The payment page may be found here - https://www.audiokarma.org/support.html

902 mounting studs

RonSSNova

RonSSNova

AK Subscriber
Subscriber
So, I had the 902's sitting on my work bench waiting for the new owner to stop by and pick them up.
Got up in the AM to find one on the ground (concrete) with a stud busted off.
Since we didn't have an earthquake in Oregon last night.......it was the cat. Must have thought it was a roll of toilet paper.

Anyway, has anyone figured out the thread in the driver itself? Dimension say it might be 12-24? Obviously not 1/4-20.
I can see a mess trying to tap it to 1/4-20. The entire driver attracts shavings etc. BIG TIME.

Ron
 
Register to hide this ad
I would be more concerned about the potential damage to the magnet and did the voice coil gap change and possibly damage the Diafraghm ?
 
The plot thickens of course. Pulled a stud out of the 2nd 902 and found this.

IMG_2614.jpeg

Different threads on the driver side.
The larger one that I need replacements for won’t screw in to the 2nd driver.

The busted ones are .212 dia and after measuring I believe are 27 threads per inch.

Nice consistency Altec
 
Hardware store. We have a very good one here.
12-24 is the thread. So two long screws, cut the heads off, blue loctite, and two 12-24 nuts (still 7/16 wrench) done!
Cost $1.75
IMG_2616.jpeg

And yeah, the screw in things at the hardware store very helpful.
Thanks
 
These drivers have been repaired as the stepped studs were used to fix a stripped out body. Original 902 studs were 1/4-20's with 20 turns per inch.

Altec Lansing 902 compression drivers use 1/4-20 threaded mounting holes/studs. (with the mounting holes typically measuring about 0.380" to 3/8" deep in the body).
  • Thread Size: 1/4-20 coarse thread (1/4" diameter, 20 threads per inch).
  • Stud Configuration: Typically features two mounting studs spaced 180° apart on 1-1/2" centers (or standard 2-bolt horn mounting patterns depending on the specific variant).
  • Depth: The threaded wells inside the driver body are roughly 3/8" (0.380") deep.


Yes those are "Stepped Studs" specifically unequal double ended studs. The narrow portion on Ron's picture is 1/4" stepped up to 5/16"

Why Altec Lansing Used These
When installing or servicing heavy vintage drivers like the Altec 902 series, it is incredibly common to run into this configuration for a couple of specific reasons:
  1. Repairing Stripped Holes: The 902 driver housing is cast from a relatively soft aluminum alloy. If a technician over-tightened the original 1/4-inch mounting bolts, the internal threads in the driver's body would easily strip out. To fix this without buying a new housing, the standard repair is to drill out the stripped hole, tap it to a larger 5/16-inch coarse thread, and use these stepped studs.
  2. Preserving the Horn Fit: The 5/16-inch side screws permanently into the newly enlarged hole in the driver body. The stud then steps down to a 1/4-inch thread on the exposed side. This allows the driver to still slide perfectly into the standard 1/4-inch mounting flanges of original Altec horns (like the 811B or 511B) without forcing you to modify or drill out the holes on your vintage horn throat.

I always recommend hand tighten the best you can and be extremely careful whenever you apply a wrench to the nut as they will strip out quite easily ! I made that mistake, many, many years ago !
 
Last edited:
Sorry. No 5/16 here. Studs are 1/4-20 and the portion that threads into the driver on this one is 12-24. Which is a machine screw thread.
The other 902 has an even smaller step where it goes into the driver.

I have 3 more pairs in use, one pair being 902’s. But I’m not going to disassemble cabinets to remove studs to look see
 
No don’t do that Ron ! But for the most part the 5/16 was really only used for repairs of stripped out bodies.. When the 1/4-20’s were stripped..What i meant was the double ended studs were used strictly for repair of stripped body threads … But we all know that Altec used many different methods over the years as it seems whatever they or field technicians had on hand.. One thing is for certain if your drivers have stepped threads they have been repaired. The aluminum alloy Altec used was incredibly soft IMO.. Too soft another cost cutting measure IMHO !
 
Last edited:
You must log in or register to reply here.
Back
Top Bottom