[Elecraft] K2 # 4498 - Electrostatic protection

[G3VVT at aol.com]

In a message dated 21/01/05 16:18:13 GMT Standard Time, ars.f5ul at wanadoo.fr  
writes:

I'm in a  very stormy country (Northern Alps) and we have at least once per 
month a  thunderstorm that already cost me one pair of power Xstors (in my 
TS-130 -  $380!!!) so even with $5 each TO220 part, I did not want to loose them, 
or at  least reduce the chance to loose them.

So I instaled on the KAT2  control board an RF Chock (1 mH) and an NE2 neon 
bulb wired between K18-pin  3/8 and ground just to establish a direct lway to 
ground for static  electricity (via the chock) and in case of a virulent one 
turn on the NE2 and  establish a full short to ground. 




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Hi Robert,
 
It is normal practise to install an RF choke directly across the antenna  
socket of tube (valve) PA to protect in case of a failure of the coupling  
capacitors from the tube anode.
 
2.5kV can be very damaging to your health!
 
Suppose these have ceased to be used since the move to solid state PA's.  
>From memory 2.5mH was the normal value used in the last one I built in the  
1960's. The addition of a neon to hold off the path until the neon strikes  should 
not represent any problem though am not entirely sure that it is  necessary 
not knowing the KAT2 circuitry.
 
In professional communication terminal equipment that is connected to  
external lines the inclusion of gas or carbon arresters is a standard feature at  
the point where the external line is connected. In addition all of our telecom  
distibution frames and even the distibution pedestals had arresters built in 
as  standard. The protection operation point was selected to be higher than the 
 normal operating voltages on the line. A QRP K2 is listed as providing 70 to 
80V  across 50 ohms and the normal striking voltage of a neon is about 110V, 
so the  neon should not strike. There are however some neons on the market 
that strike  at a lower voltage somewhere in the 60V region and to our cost we 
found these  put a S/C across the phone line when ringing voltage and normal 
telephone  battery were present. These would also operate when the K2 was giving 
normal PA  O/P.
 
Probably the choke on it's own would be entirely sufficient to provide the  
protection needed as long as the component was able to handle the current  
required.
 
Bob, G3VVT
K2 #4168