Installing a new diaphragm into an Electro-Voice T35 or T350 is a little easier than shown here, the reason being that some very old T35's didn't have the centering ring cast into the head assembly.  This ring allowed the diaphragm to be inserted without the use of a shim (yellow) as shown here.  This is the result of habit and it was left here just in case anyone had a very old unit to repair.  The shim is 0.005" thin and is about 3.0625" (3 1/16) and will have to be trimmed shorter to fit inside the coil.  It is 1/8 to 3/16 inches wide.
The two left diaphragms are new but note the solder joints on the left one.  If the gasket is not used, these joints may touch the top plate of the magnet assembly and short the voice coil.



If you look closely at the coil, you will see a dark vertical line on the winding.  This is the return end of the coil as it is a single layer coil.  The top plate of the magnet assembly has a notch to provide clearance.



The T-350 unit with the four fillister head screws removed.


The horn removed from the head.


The head removed from the magnet assembly.  Note the notch in the top plate at 9 o'clock.  This is to provide clearance for the return end of the coil.


The gasket removed from the diaphragm assembly.  It was damaged due to old capacitors in the pre-amp which sizzled and popped once too loudly and have since been replaced.

The cost of procrastination.


Another view of the return end of the coil.


The shim inserted into the coil.  This isn't necessary on newer tweeters as the head has a ring into which the coil assembly fits snugly and self centers in the gap.

Some older T-35's have been seen that didn't have this centering ring, thus necessitating the shim.  The diaphragm with shim were then inserted into the gap with the return end oriented to the notch. Glue is applied to the outer ring of the diaphragm and the head mounted, being careful to observe the polarity.   Once the glue has set, the head, diaphragm and shim are carefully removed vertically and the ship removed from the coil.  The diaphragm is now centered.

To check the polarity of the coil, it is placed without the shim into the gap.  A weak AA battery is momentarily connected to the coil leads.  When the coil jumps out of the gap, the polarity is marked to match the battery.

Once the coil and shim are placed back into the gap, polarity must be remembered so the head can be placed accordingly to coincide with the terminals there upon.

It has been my experience that the positive end is the lead farther away from the return end of the coil.



This unit has a thin rubber gasket  in the centering ring which was not noticed on some previous units.  The adhesive was carefully removed so as not to damage this gasket.

Note the tab space on the far right of the centering ring.  There is another diametrically across.


The red line marks the return end of the coil.  The lead on the right is the positive; note the red + sign above the lead.  I also marked the negative with a green line, the result of habit from repairing some of the very old units.  It's easier to see the green through the diaphragm when inserted in the gap with the shim.


Diaphragm soldered.  It's highly recommended to use a small alligator clip on the lead to act as a heat sink.  The solder is applied to the units terminals which are large enough to require substantial heat which, if not sunk, may melt the lead to coil solder joint.


The gasket applied and marked to show the location of the return wend of the coil.  As mentioned earlier, the positive lead is the one farther from the coin return end.  It's easier to see that here.  the positive binding post has a red gasket.


The assembled and working T-350




Back to the loudspeaker main page