The AM Forum

OK, I am trying something new for me...I am attempting to rebuild a
Shure crystal mic element...
The original is a little smaller in diameter than a D-104 element.
I removed the diaphragm from the Shure element, then
replaced the xtal element with a Kobitone xtal element.
My question is:
Any suggestions how to replace the diaphragm and attach it to the element?
NEXT QUESTION:
I have a beautiful Astatic 77 dynamic mic...
the output is weak...does anyone out there have experience rebuilding them?
73
Steve
8tow

Lots of choices for elements: http://www.kenselectronics.com/lists/micpart.htm (http://www.kenselectronics.com/lists/micpart.htm)

Rebuilding/restoring your 77 to original condx could be pricey. Most guys avoid drilling and blasting and glue a little Radio Shack Electret Element (was PN 270-092C) in next to the original element and lift DC off the mic circuit or a battery.

The Heil HC5 element werks real well here, it's a little box element, a little Velcro or a little adhesive......and no DC to spring in....Much better Fidelity, those old units were real Thin on Bandwidth.

Double sided tape would be better I think, a little separation from the element and the case is important...Isolation..It vely helpful..

73
Jack.

All of life's really important problems can be solved with a bigger hammer  ;)

Post an image of the innards?

The center post on the D-104 element is held to the aluminum diaphragm by a wax. Geez, at the moment I don't recall what wax it is, but I'll bet it is the same stuff that was once used for seals on letters!! My mom had some sticks of that in here pencil drawer in the desk when I was a kid.

The edge of the element is held by an adhesive glue. You could use a rubber glue like "Pliobond" or even some silicone rubber (although that won't stick right away). The other possiblity is some contact cement, but that gives you one shot only... no slop.

That should work ok.

Crazy glue gel is another possibility if ur careful and surfaces are clean - probably not clean... so rubbery glue like Pliobond is probably best... "Goop" is possible too... apply sparingly and precisely...

               _-_-bear

PS, are you sure the old element itself is bad?? maybe just the wax broke off the diaphragm??

I have a couple of defunct D-104 xtal elements, both removed from hamfest "bargains".  One has very low output but appears physically intact, while the other sounds extremely tinny and distorted.  On the distorted one, some idiot not only severely dented the diaphragm, but punched it full of holes like what you would see on a salt-shaker.  I can't imagine what he could have been trying to accomplish.

I am going to try to disassemble both elements and see if I can use the good diaphragm to replace the mangled one on the element that appears to still have a good crystal.  I am not sure what kind of bonding material they used between the crystal and diaphragm, but with any luck, it can be melted by careful application of heat without ruining the crystal.  The other tricky part will be to detach the edge of the diaphragm from the bakelite case without damaging it.

Has anyone here ever disassembled one of those elements, and figured out what they used for bonding material?

Later D104 elements came with one hole punched in them.  There was an article about this. I cant remember where or when at the moment.  However, It showed the effects of punching more holes in the metal.  One small pin hole will add alot of low to midranger to the Cartride. I am not sure why. Maybe it lets air out so the overall movement is increased? 

I do know that I have maybe 10 D104 heads and several of them are punched with 2 or 3 holes. These seem to have a more full sound to them.

Clark

Years ago I bought a new element from Astatic and when it arrived, I thought the fibreglass insulation in front of the diaphragm was packing material, so I removed it.  There was a hole in the little round cardboard box it came in, so I thought the hole in the diaphragm was due to shipping damage, and I sealed it up with a drop of epoxy, out of fear that the hole would let in humidity and ruin the crystal.  I think the holes in the cardboard box and the one in the diaphragm were unrelated.  I don't recall there being any fibreglass in front of the diaphragm of the element I replaced in that microphone.  But as far as I remember, the new element sounded as good as the old one did before it crapped out.  But I got rid of that microphone a long time ago.

They should packed a small note about the insulating material and the hole with the mic elements.  I'm sure I'm not the only one to have ever made that bone-headed mistake. 

Don,

That's wax holding the center of diaphragm... a little heat melts it nicely. Smooth application of an xacto knife below the diaphragm (face the blade to the plastic...) and/or fingers will lift it. Check the wax on the "bad" one with an eye loupe or similar to see if it is micro cracked, causing no output. If cracked reheat with a small soldering iron, and try again...

            _-_-bear

...just noticed this guy selling replacement D-104 elements.

http://www.rbmicro.com/index.php (http://www.rbmicro.com/index.php)

He has a sound file of an A/B comparison between his replacement and the original. Very interesting.

I agree. The Heil elements never sounded even close to a D104 cartridge.  It was a waste of money. I ended up installing that element into an old Yaesu mic that had a bad element and I use it on a SSB rig.

The kits you see on the net and the replacement elements you find are nothing more then Telephone cartridges. These come from the EAR piece of a standard Cradle telephone. NOT the mouth piece.  You can use the mouthpiece if you want but the Ear piece is better. 

YOu can pick up these phones for free or for next to nothing. They made Millions of them. THe old Rotary style or the push buttons will work. 

Clark

Did you try the earpiece?

The Mouthpiece is real tiny.. Like a phone..LOL.

Clark

Mouser has some crystal as well as other elements.

Some are fairly wide-banded, too.  And at less than 7 bucks a pop, you can't beat them!

I've had good luck with them in the past.

--Shane

LOL.. The Mousers are all old Phone elements..  :)   Some work ok though!

Clark

The big trouble is the low impedance..  Almost all of us need high impedance mics.  Those are listed as 9 ohms.. Yeah.. Beause its really a speaker not a mic element.

A bunch of guys on top band all purchased the mouser ones and I thought they sounded horrible. I mentioned they where Telphone ear pieces and they joined forces and argued.  THen one of them actualy still used that still phone.. He opened up the ear piece and confirmed it was the same.. It was a joke for a few months.

If they work for you then great.. But most of the time.. I never was happy.  I have my favorite D104 head.. Its the old type with Black screws. It came off of an old Demco CB set I had.. For some reason it has the richest tone and highest output.

Clark

Mouser sells 3, stocks 2.

The round ones, that are also marketed as the replacement D104 elements are in fact the telephone ear pieces.

The square elements, at 200K impedance (230K sounded muffly, 200K on the source sounded good) are low impedance by boat anchor standards, but a simple fet can fix that, or a transformer.

Or, they actually match up fairly well, in stock trim, to an amplified P stand, which is what I used it in.

--Shane

Yeah.. i played around with resistors on my GLobe Champion 300. This resistor loaded the mic element. I was shocked at the difference in sound when changing from one to another. I ended up using a 2kohm 1/4 watt. This really made the rig sound smooth.

Clark

I really started figuring out how important impedance matching was for audio in the last 5 or so years.  Before that, it was stuff it in, and if it didn't work, the mic was junk.  Then I discovered WHY my unamplified Astatics sounded SO thin on solid state stuff.  Never looked back since.

I had a test jig set up here for crystal style / high impedance mics.  It had a 20 megohm (iirc) pot across the input to load the elements at different levels.  THAT'S what taught me about impedance matching.

Then I looked around this site, and thoughts really started taking off.

--Shane

Yeah.. I keep looking for an old Resistor "wheel" at Ham fests. The ones with clip leads so you can just turn the wheel and try all different values. 

Clark

The old type heads had chrome plated screws. The name plate was metal and riveted onto the head, and each mic had a unique serial number.  The later ones have a generic plastic stick-on name plate with no serial number.  The really old ones (pre-1937) are a full 1" thick.  After that date, they were trimmed down to 13/16".  I have never seen one with black screws.  Given that it came with a CB rig, I suspect some Good Buddy decided to "spiff" it up with black paint.

I run my D-104 into a 10 megohm load.  An experimental project in the works will use a balanced push-pull input stage, with a 10 megs grid leak for each tube, to give a total of 20 megohms load for the D-104.  It appears that the D-104 responds to very low, near subsonic audio frequencies.  I use mine in combination with a dynamic. The D-104 seems to cut the lower voice frequencies, so mixing in the dynamic as a sort of "woofer" adds more bass (but not too much) to the voice.  But I sometimes notice what looks like a.c. hum on the scope, modulating at up to 50%, with what looks like a pure sine wave.  I checked it out, and it is the D-104 that picks it up.  It goes away with only the dynamic connected.  I finally figured out what it is - distant aircraft that I cannot even hear with my own ears.  Whenever the "hum" appears on my scope pattern, within 2 or 3 minutes, I can hear the aircraft as it approaches - usually a helicopter.  It will be interesting to see how well the lower voice frequencies come through with a 20 megohm load.  I plan to use a push-pull stage because one tube might not be stable with that high a grid leak.  The only modification I will have to make to the D-104 will be to replace the single-conductor shielded mic cable with a two conductor one.

Astatic made, in the last 15 or so years, a mic called the night eagle. 

They also where commissioned by Galaxy to make a Galaxy series "Silver Eagle" amplified base.

Both had black screws.


--Shane

Lots of guys are selling the Telephone elements.. I just wanted to point that out so people would understand what they are buying..  I never liked the sound.

kyv.  Before becoming a ham, I was of course, A CBer..  :)  For years and years I collected a huge amount of told tube sets. For some reason I got into Demcos.  I had several Satalite base stations.  All of them came with an unpowered D104 mic. All had Black screws. Clearly. They are not repaints. In the manual it shows the Mic with a black and white photo and it was black scews. Probably done by Demco themselvs as the radios where Black and Silver.  In the manual this was called the "crystal" D104 mic.  Maybe I should pop it open to see whats inside?

Not sure why it is my best element. I have the Very old, Old and new elements. I always liked the middle years. Most of the really old ones I had where bad or went bad. I have a few of the Gold plated ones made to match the Browning Golden eagle base stations. These are stamped Browning on them. THey had Red Grill cloth and are not powered.  Standard MC-320 elements.

One thing that you probably know is that most of these heads all sound a bit different. I have swapped them around over the years and you can really tell on the output and sound. Alot of this is probably due to the age/modifications and condition.

If you like microphones, Look up the guy on ebay that sells old mics for mouth harp use. He has a video for each mic of him playing the harp. I am sorry to say I spent an hour the other night listening to many different types of turner, Astatic and EV mics.  His recording is pretty good and I could really hear the difference. His 638 recording sounds... Like a 638. His 634 recording sounds just like a 634. 

Above I said I used a 2k ohm resistor.. Thinking back.. This was really a 2meg resistor.. Dons post jarred my memory.. On my Champion 300, the 2meg seemed to work best. The original value was 1k and the audio was thin.


Clark

Astatic recommends 5 megohms.  Supposedly a crystal microphone element is equivalent to an ideal a.c. generator with about a 500 pf capacitor in series.  So naturally, the higher the load resistance, the better the low frequency response.  The only reason you need any load at all across the mic is to provide a grid or gate return to ground. Tubes tend to collect charge on the control grid and the plate current becomes unstable if the grid is left floating or the grid leak resistor is too high.  10 megs is about the upper limit for the grid leak with most tubes.  But in a push-pull configuration, each grid can have its 10 meg leak, making the total load 20 megs.  The D-104 xtal element is built symmetrically, with no "hot" and "ground".  You simply have two terminals from the Rochelle salt crystal coming out of a bakelite case.  A two-wire conductor mic cable is used, with the shield connected to the shell of the mic, and the leads from the mic elemint  going to the two grids.  The common ground connection at the bottom ends of the two grid leaks forms the midtap.  The grid leaks should be carefully chosen to have the same resistance, for minimum distortion in the push-pull circuit.

Yeah.. The demco modulator.. haha.  I still have a few of those in the closet. Just a Mic preamp.  I forgot about those..

Clark

Somebody here mentioned the $3 electet from Shady-O-Rack. I'm here to tell you, they are every bit as good as the D-104 quality audio. Don't dismiss them until you actually hear them on the air. Very surprising!

Acoustic housing, placement and mounting of a mic element can have dramatic influence on sound. Quite a while back when I was fooling with SSB, I removed the electret element from an Icom SM-6 mic and installed it in a more substantial Shure 'high ball' mic (and relocated the preamp into the case as well). I tried all kinds of direct mount and floating element suspension schemes, but it never sounded as good as the original Icom case that consisted of a close fitting metal tube with a hole about 1/8" from the element.

I might have one...  I will dig around for it.. I know I have the manual for it somewhere.  I think its only two tubes...

Neat little unit.. It worked well on the Demco radio.. It was a total wimp without it. 

Clark

 Hello Steve,
  Looks like a topic ripe for rampant digression.

 In the Turner mic that I did years ago (the one I gave to you) I simply heated and removed the aluminum diaphram very cleanly. I then took one of the Mouser (Kobitone) small crystal MICROPHONE elements and began a disection. First I removed and discarded the OEM diaphram. Step two involved trimming the drawn steel cup that forms the shell to a suitable thickness. Leads were placed and soldered from the Kobitone replacement and the Turner terminals. Now the Kobitone is set in epoxy with the crystal stirrup center offset by one stirrup width. At this point I Cyano-glued the Turner stirrup to the Kobitone strrup so as to duplicate the postion it held in the original Turner configuration. Now the diaphram is Gorilla glued in place with the stirrup tip slightly protruding as it always had. The stirrup was also glued with a dap of partially thickened by pre drying Gorilla Glue.

  As you well know, it works just fine.

  As far as the Astatic 77 , I have several of those. More often than not, when shipped they arrive with the element flopping around within the case ! The mounting "adhesive" has long since turned to a dry clay like crud. At that point a secondary problem often presents itself. Seems, as luck would play the .002" element coil leads are often severed by sharp corners within the case as the element bounces about . Often they are severed when crushed between the fibreboard lead out backing and the sharp corner they are impacted against.
  With a little patience, good magnifiers and a ton of luck the leads may be repaired.
 A little more ingenuity will lead you to suitable rubber and adhesive to effect a remounting of the element that should last another 50 years. I recently bought 2 Astatic 77s that once belonged to the legendary Roy Orbison. Both of them were DOA with the bouncing element syndrome. I also had tow others that were not working from open coil damage. The Orbison Mics were just the incentive to get me to attempt repairs. After finding near identical problems on the first two and successfully restoring function I had the confidence to undertake the "O" mics. They too responded well and are now in my son's mic collection.

 The 77 as you know has an impedance selection switch and allows low, medium and high impedance matching. It important to use the proper terminal connections as well.  If you need them, I have made some tools up that allow for clean removal and tightening of both the impedance switch recessed nut and the tilt position split drive nuts. Let me know if you would like to borrow them. That way you won't have to risk damage from a slipping screwdriver or other mis-applied substitute  "tool" !

  Good luck Steve.

 Gary 'LB