Call Search
     

New to Ham Radio?
My Profile

Community
Articles
Forums
News
Reviews
Friends Remembered
Strays
Survey Question

Operating
Contesting
DX Cluster Spots
Propagation

Resources
Calendar
Classifieds
Ham Exams
Ham Links
List Archives
News Articles
Product Reviews
QSL Managers

Site Info
eHam Help (FAQ)
Support the site
The eHam Team
Advertising Info
Vision Statement
About eHam.net

donate to eham
   Home   Help Search  
Pages: [1]   Go Down
  Print  
Author Topic: Mic Mystery  (Read 1049 times)
N4KYW
Member

Posts: 146


WWW

Ignore
« on: December 21, 2018, 07:41:58 PM »

I just bought a Turner crystal mic model 141-11 (high impedance) to match the requirements of my vintage rig, a Clegg 99er. The mic even came equipped with an RCA plug to connect right up to the rig's RCA  jack. The mic is NOS, about 58 years old.

However, while attempting to use this mic I received reports of signal but no audio. Is it possible for the mic's crystal element to have "petrified?"
Logged
G3RZP
Member

Posts: 1319




Ignore
« Reply #1 on: December 22, 2018, 03:41:40 AM »

Very likely. Many crystal microphones used Rochelle salt in the element and it absorbs moisture over the years, so losing its piezoelectric property.
Logged
K2LGO
Member

Posts: 180




Ignore
« Reply #2 on: December 23, 2018, 08:18:50 AM »

It appears that the mic is indeed keying the radio....Is the RCA plug that came with it a four pin plug, so that you can safely assume that the two contacts on the mic plug that are not the keying plugs are the audio output, that should go to the xmtr...As a last test, I try any mics of that era I might get on my scope, and usually I can see if the output is present...
Logged
N4KYW
Member

Posts: 146


WWW

Ignore
« Reply #3 on: December 23, 2018, 08:38:37 AM »

Thanks, K2LGO. Perhaps I should have described the connector better. It's a simple RCA phono plug. The mic cable has just a center conductor surrounded by a coaxial shield. There is no PTT function on this mic. That is handled by an impressive switch on the front panel of the Clegg 99er.
As a first step I really should have the mic output checked. At home I have nothing to plug it into, so I guess I'm going to have to rely on one of my ham radio buddies to test it for me.
73,
Howard
Logged
VE3WGO
Member

Posts: 451




Ignore
« Reply #4 on: December 23, 2018, 10:40:23 AM »

those Rochelle salts are part of the piezoelectric salts family.  They very easily absorb moisture, in fact similar salts are used in those Desiccant packages you often see when you buy something that needs to stay dry, like maybe electronics, or food.

Before throwing that old "crystal" microphone away, it might be worth trying to open it up and drying out the salt, if it can be accessed without destroying the mic element.  Most desiccants can be dried out or "recharged" using some modest heat or even microwaving them in a cooking pan for a couple of minutes.  I don't know if the salt in the old mic is too far gone to do this, but it might be worth a try.  Google something like "recharging desiccant packs" to get some advice.

Or else, do what many have done, and convert the mic to an electret element with a tiny built-in preamp.  It can work well but that's not true vintage.

73, Ed
Logged
G3RZP
Member

Posts: 1319




Ignore
« Reply #5 on: December 24, 2018, 01:40:56 AM »

My father, back in the late 1950s, popped a dying crystal microphone in the kitchen oven at about 75 degrees for 45 minutes and restored it. It eventually died though, but had been baked about 3 times prior to death....
Logged
K1DA
Member

Posts: 744




Ignore
« Reply #6 on: December 30, 2018, 11:43:28 AM »

The plug you refer to is a "phone plug" not an "RCA" plug which is found on older stereo equipment.   Phone plugs come in two and three conductor variations.  The three conductor version is often used on stereo headphones.  Drake and Collins used a slightly smaller diameter version of the plug for their mike connections and the 1/4 inch mono version
for headphone plugs.  The smaller version was also used in many telephone switchboards. 
Logged
WA2CWA
Member

Posts: 568


WWW

Ignore
« Reply #7 on: December 30, 2018, 03:13:06 PM »

Microphone gain control is on the back of the transceiver. If it's turned the wrong way, there is no transmit audio.
Pete, wa2cwa
www.manualman.com
Logged
Pages: [1]   Go Up
  Print  
 
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.11 | SMF © 2006-2009, Simple Machines LLC Valid XHTML 1.0! Valid CSS!