Electrostatic Tweeter repair and restoration.

This is a German made electrostatic tweeter. It has failed like so many others of this vintage. This tweeter is from a 1959-60 Emud Junior 196 six tube AM/FM radio. There were three choices involved with this speaker, leave it in the unit dead, find a replacement that works or repair the existing speaker.

If one wiggled the positive contact while playing the radio the sound would cut in and out. It was a quite subdued sound but present none the less. So see below the steps to restoring this Electrostatic Tweeter speaker.

Note below the three main problems that contributed to the failure of this speaker. All caused by deteriorating foam.

The first step was to remove the speaker from the cabinet. You can see the two contacts on the tweeter. One contact is the actual metal perforated grill of the speaker (ground). The other is a loose and floppy silver contact (positive 170 volts DC through a 100k resistor! It will bite you, Ouch!).

With so much DC on this speaker one must ensure cleanliness and the integrity of the internal components do not create a short circuit. The 100K resistor would protect this particular radio but this is no guarantee in other radios.

A Dremel Moto tool with a sandpaper disk made quick work of the formed plastic retainers that hold the assembly together. Note: Leave as much plastic as possible. It will be re-flared with a hot soldering iron to hold the assembly together.

An alternative is to drill out the rivets and use tiny machine nuts and bolts to hold the assembly together. Use Glipt, Loctite or old fingernail polish to lock the nuts to the threads. This assembly vibrates since it is an electrical to physical transducer to vibrate air waves.

	This picture shows the internal components of the tweeter.
	Lower right is the silver contact that has significant corrosion on it.
	The upper left is the delicate extremely thin plastic like membrane. It has a conductive coating on one side that is press fit to the silver contact mentioned above.
	The silver item in the middle is the perforated grill. It has a deteriorated pieces of foam on the right side that pressed the membrane to the silver positive contact.
	The lower left brown item has some dry rotted foam that presses the membrane against the perforated grill.

Problem identified - Deteriorated Foam.

This was the main problem. Deteriorated foam that causes a poor or no "press fit" connection between the silver contact and the membrane.

	Seen here is the corroded contact, the deteriorated piece of foam and the cellophane tape that I think insulates the positive contact from the negative perforated grill.
	I have seen this type of foam stain, corrode and ruin what ever it is in contact with including dial scale printing.

This was the second problem with the speaker. The foam corroded or coated the silver contact with crud.

Burnish and clean the silver positive contact with fine grit sandpaper.

This was to a lesser degree, the third problem. This foam backer was not pressing the membrane close to the negative electrode (the perforated grill).

Cut out a new replacement piece of foam that holds the membrane against the perforated grill

Reassembly - Put it back together

Assemble in order:

	Perforated Grill
	Electrical tape
	Double sided sticky foam tape from Radio Shack.
	Membrane. Be careful to maintain the orientation of the conductive side true to the disassembly.
	Place the silver positive contact in the plastic cone.
	And replace the brown deteriorated foam with your new piece that you cut or fabricated.
	Press the assembly together and flair the plastic rivets with a hot soldering iron.

This picture shows the assembled speaker. The new foam piece is the other half of the foam inside the speaker. It was twice as thick as the original. I used an X-Acto blade to slice the thickness in half.

Also seen is:

	Electrical tape to replace the cellophane tape.
	Double sided sticky foam tape to press the silver contact to the membrane and
	The deteriorated foam used to press the membrane against the perforated grill. The brown foam broke apart into powder when I picked it from the speaker structural cone.

The rebuilt tweeter on the Emud sounding Great! The output is significantly greater (louder) than before it was rebuilt as compared when wiggling the previously loose positive contact.

I can't properly reproduce the sound on this web page so a hearty "Thumb-up" will have to do.

GRUNDIG 3035 w/3D USA

This is a flat square electrostatic tweeter from a Grundig 3035. It had a corroded contact that is press fit against the conductive vibrating membrane. Disassembly and sanding off of the corrosion where the contact touches the membrane is all that was needed.

Use a hobby grinder to take off the tops of the melted plastic rivets	Test the side with out lead wires by prying up.	You may need a little more grinding to remove the retainer side with the lead wires.	Lay all the part out on your bench. The white material seems to be wool. That is used to keep the conductive membrane close to the metal screen. The wool is much better than the foam rubber.
Identify the corroded contact the is press fit against the membrane and a strip of foil seen on the right of this picture. Use sand paper or your favorite burnishing technique to remove the corrosion.	Reassemble the unit and test before melting the rivets.	Melt the rivets, use glue or hot melt glue to hold the tweeter together.	Sounds Great!

To see other Tweeter restorations see:

Telefunken page

Blaupunkt Page.

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