[Boatanchors] D-104 Replacement Element Topic Change Turner 22X

[David C. Hallam]

I have a Turner 22X that needs a replacement cartridge and have one of 
those Kobitone elements I bought from Mouser several years ago. But, I 
have never tried it.  Is there a better replacement for my microphone or 
should I go ahead with the Kobitone.  It would be used with 
Hallicrafters and Johnson rigs.  I currently use either a EV 676 or 
Turner 95D with an Invader 2000 and was using the Turner 22X with my 
HT-32B, but now use another Turner 95D with it.

David
KW4DH

On 6/17/2014 12:07 PM, Richard Knoppow wrote:
>
> ----- Original Message ----- From: "Rob Atkinson" <ranchorobbo at gmail.com>
> To: "Mark K3MSB" <mark.k3msb at gmail.com>
> Cc: "Boatanchors List" <boatanchors at mailman.qth.net>
> Sent: Tuesday, June 17, 2014 6:38 AM
> Subject: Re: [Boatanchors] D-104 Replacement Element
>
>
>> Not me, but it is interesting.  I think the original element had a
>> bigger diaphragm.  Not sure about the Z.  I had some idea the original
>> impedance was several megohms.  I see this new one is 25K. I'd say
>> that if you get one and it works out okay, order 2 or 3 more. These
>> small companies have a way of suddenly vanishing.
>>
>> 73
>> Rob
>> K5UJ
>
>     Crystal microphones (and phono pickups) are peculiar because the 
> impedance is mostly capacitive. The reason they need such a high load 
> impedance is that the capacitance acts with the resistance of the load 
> to form a high pass RC filter.  If the load is too low the lows are 
> rolled off. Also, any parallel capacitance from the connecting cable 
> acts to lower the level.
>     Crystal microphones and phono pickups were popular because they 
> had very high output level, thus saving the need for more electronic 
> amplification, were relatively cheap to make, and could have quite 
> good fidelity.  The D-104 has a rather steep peak at around 3500 hz 
> and rolls off below about 200 hz. This was done delibrately to 
> accentuate the speech range that contributes to intelligbility.  
> Astatic knew how to make flat frequency response mics, for example the 
> T-3. The characteristic of the D-104 is partly from the diaphragm 
> resonance and partly from the rather large case which causes a rise in 
> response due to diffraction. Any element installed in the case will be 
> affected by the diffraction rise but may not have the same response as 
> the original.
>    Unfortunately, crystal elements are vulnerable to heat, moisture, 
> and mechanical shock. Astatic was pretty good about their method of 
> sealing against moisture but the heat problem is inherent in the 
> Rochelle salt material. I've forgotten the limit but its pretty low, 
> say around 105F. The crystals can be fractured by mechanical shock, 
> say from dropping, or from a strong electical signal or direct action. 
> The latter two are not important for microphones but crystal elements 
> used for phono pickups didn't like being scraped across a record and 
> those used for cutting records could be damaged by overdriving.
>    Ceramic elements began to replace crystals when they became 
> available. The output level is signifacantly lower (for the C-104 is 
> about ten db lower than the D-104) but they are a lot more rugged.
>    All of these have been pretty much replaced by other types of 
> elements since the cost of amplification is now insignificant.
>    Most crystal mics were intended to be worked into an "unloaded 
> grid", meaning something like a tube amp with a grid leak and input 
> resistance of at least a megohm.
>    Somewhere in my e-mail I have the name of some outfit that makes a 
> replacement kit for the D-104 including some shock mounting material, 
> I will try to find it and will post it here if I do. I have no idea 
> how close this kit is to the original.
>
>
> -- 
> Richard Knoppow
> Los Angeles
> WB6KBL
> dickburk at ix.netcom.com
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