How I repaired my d-104 element

[W3RSW]

Frank's (W4FLN) great find of a NOS d-104 element prompted me to write of the repair of one that was given up for trashed.

Having nothing to lose after inadvertly pushing the mike off the desk when sliding over the inevitable pile of papers, books and gear living in front of the 32v, I tried what might be a novel solution.  There has been so much similar written that this may not be quite the new idea.

The element appeared fine, purple bead on diaphragm seemed ok, but audio was extremely distorted.  

I took a pair of hemastats ( surgical locking ) clipped them on the little crystal metal mounting head that sticks up through the bead. Hung a pair of pliers for weight through the heme finger loops, then held a soldering iron up under the whole thing so the element tip was about  quarter inch away from the bead, then held there until I felt the bead might have softened.  Cooled off, reinserted element in housing and darned if it didn't come back, full fidelity.

My first thought was to simply scrape off the bead and re-attach with RTV or similar, but the bead was just too hard and trying to remove it would damage the aluminum diaphragm.  Second thought was to simply just glue around the top of the bead but got to thinking that some crystal pre-tension might have been lost when the bead bond broke so maybe a slight weight pull under tension while bead was soft before re-binding the bead would work better.  

Probably several failure modes for the crystal mounting, but in this case it was repairable. Maybe just luck but the uncalibrated weight, heat and premise worked FB.

[WBear2GCR]

the bead is a type of wax, afaik.

                  _-_-

[W3RSW]

Hard wax, gets harder with age, like in my ears 
Might have been letter sealing wax way back in the Astatic day for all I know.

[W2VW]

I have heard the WACS recruited old maids for the war.

[W3RSW]

Wrong ones.
"Everybody knows" old maids hear better than old men.  Less wax in your..um, fax, with about twelve other words that rhyme better.

So back to the pre-tension. Maybe along with crystal activity, different element tension on the diaphragms is why some D-104's are more sensitive or have better fidelity and/or bandpass, freq. response into a given load than others, even when new.
Probably had some pass/fail QC at the plant back then.

[WZ5Q]

hmmm...the pre-load is interesting...

When I repaired my D-104 element due to the "anvil" coming loose from the Rochelle Salt Crystal, I took great pains to prevent any sort of pre-load at all on the Crystal before melting the wax to re-attach the "anvil" to the diaphragm.
I also have excellent full fidelity out of the repaired element.

A Bic Lighter melts the wax FB.

73,