[Johnson] Viking 1 "gotchas" ?

[Bry Carling]

Many thanks Richard. 

Richard Knoppow <1oldlens1 at ix.netcom.com> wrote:

>
>----- Original Message ----- 
>From: <tbs50a at aol.com>
>To: <bcarling at cfl.rr.com>; <burnsguitar at yahoo.com>; 
><patrick at ae1pt.com>
>Cc: <Johnson at mailman.qth.net>
>Sent: Friday, February 22, 2013 7:53 AM
>Subject: Re: [Johnson] Viking 1 "gotchas" ?
>
>
>> Hi Brian and Bry,
>> One the V1 a few thinks come to mind. Bry mentioned the 
>> final toob.Oringinally it used a 4D32 but at one time they 
>> where very expensive is Johnson came up with a mod to use 
>> a 829B.The output is a little less abt 85wt vs 120wts. The 
>> 4D32 was abt $100 vs $10 for the 829B. In the 1990's a 
>> bunch of the 4D32's hit the surplus market at $20.\
>> Always make sure that you have grid drive to the final 
>> before you apply the HV. Originally the V1 didn't have a 
>> clamp toob so you can wasted the final.
>> Three things come to mind on the electronics.The voltage 
>> divider resistor R13? 15K 50watts Usually open..When open 
>> you won't have screen grid voltage on the mod & final 
>> Clean the meter switch really well. And pull out the 
>> roller inductor and clean it too.
>> Bry, On your D-104 I read somewhere that in the cartige 
>> there is a diaphragm with a pin in the center of it. That 
>> pin has a wax seal on it. Use heat to reflow the wax on to 
>> the pin. That should fix your low fq problem. Long time no 
>> chat OM.Have been in bed all week with a bum back. If you 
>> could say a few words in prayer that would be wonderful!!
>> GL&GB
>> Terry N3GTE
>>
>
>     Most crystal microphones and headphones, at least the 
>ones with diaphragms (there is another kind) drive the 
>diaphragm with a pin. I would be very careful of using heat 
>because heat can destroy the crystal element.  They are 
>sensitive to heat and moisture.  One of the features of the 
>Astatic crystal mics was their method of sealing the element 
>to prevent moisture damage.
>     The D-104 does not have a lot of low end; this one may 
>be normal. I would compare it to another to be sure.  The 
>D-104 was designed for voice communication purposes and has 
>a steeply rising response curve with a fairly sharp peak at 
>about 4 khz. It can sound metallic or tinny.  Also, the load 
>impedance has a very strong effect on the response of a 
>crystal mic; the element looks electrically like a capacitor 
>so any parallel resistance makes it a high pass filter. 
>Crystal mics want to work into a very high impedance, the 
>closer to infinite the better, but a megohm or more anyway. 
>Many mic pre-amps present too low an impedance causing the 
>low end to roll off. Since the D-104 does not have a lot of 
>low end to begin with it becomes very tinny.  Putting a 100K 
>resistor in series with it may help.  Also cable capacitance 
>is important; excessive capacitance rolls of the high end 
>and reduces the output level. Short cables of 
>low-capacitance co-ax are necessary.
>    You can probably do better with another kind of 
>microphone. Crystal mics were popular because they were 
>relatively inexpensive for the quality and because they put 
>out very high levels. The latter was of importance when 
>electronic amplification was expensive.  The construction is 
>simple compared to a moving coil or ribbon dynamic mic but 
>the usual conical metal diaphragm limits the quality.
>    Long ago "sound cell" type crystal mics were available 
>where the crystal element was directly exposed to the sound 
>waves. These had quite high fidelity and extended 
>high-frequency response but very low level.  Brush 
>Development and some other companies made sound-cell mics 
>for measurement purposes and occasional use in sound 
>recording. They are essentially obsolete now.
>    FWIW, I have two D-104's, both sound exactly alike and 
>both sound tinny to my no longer very good hearing. 
>Currently, I am using an Electro-Voice 664, which gets good 
>reports.  There are newer mics with similar characteristics.
>
>
>--
>Richard Knoppow
>Los Angeles
>WB6KBL
>dickburk at ix.netcom.com 

regards,
Bry Carling

-- 
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