[Elecraft] Fwd: KX3 Relay Control For Desktop Amplifiers

[Jimk8mr at aol.com]

The DEM transverters also have the diode snubber.  
 
So things remain a mystery, hopefully never to repeat.
 
 
73   -   Jim   K8MR
 
 
In a message dated 3/12/2013 8:02:08 P.M. Eastern Daylight Time,  
c-hawley at illinois.edu writes:

The  2N7002 has an internal diode for any inductive collapse.

Sent from my  iPad
Chuck, KE9UW 
(Jack for BMW motorcycles)

On Mar 12, 2013, at  6:58 PM, "Rich Heineck" <richei at frontier.com> wrote:

>  Jim,
> 
> The FET shouldn't have had any problem with 50 mA.   It's a 2N7002 and is 
rated for 115 mA continuous and 800 mA pulsed, with 60V  max voltage when 
off.  One possibility is that the load being switched  was inductive (like a 
relay), and the FET's voltage rating was exceeded when  the relay was 
released due to inductive kickback.  The simplest solution  to snub the kickback 
spike is to put a reverse diode, like a 1N4002, across  the relay coil 
(cathode side to the relay's '+' supply).
> 
> It's  also possible the FET was defective or damaged to begin with, which 
led to an  early failure.
> 
> 73,
> Rich  AC7MA
> 
>  
> On 03/12/2013 01:28 PM, Jimk8mr at aol.com wrote:
>> I blew the  switching FET with about 50 ma of current (12 volts) from a
>>  DownEast Microwave transverter. Elecraft says it should have handled 
it,  but
>> anyway, FWIW.
>>  The FET has been replaced, and  an intermediate switching transistor
>> installed in the switchbox  for the several transverters. Now switching 
1 or 2  ma,
>> hope  that holds!
>>    73  -  Jim    K8MR
>>        ____________________________________
>>  From:  robertwschumacher at yahoo.com
>> To:  elecraft at mailman.qth.net
>> Sent:  3/12/2013 12:07:26 P.M.  Eastern Daylight Time
>> Subj: [Elecraft] KX3 Relay  Control For  Desktop Amplifiers
>> 
>> 
>> Most common desktop  amps have a relay circuit that requires  a 
transceiver
>> to  short 12 VDC at 100 ma to key the amplifier on.
>> In the KX3   specs, the maximum amp relay current is stated to be 100 ma.
>> Has  anyone keyed  a desktop amp directly with a KX3 or is it 
recommended  to
>> use an intermediate  external relay   circuit?
>> 
>> Thanks,
>> 
>>  W9DBR
>> 
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> 
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