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Re: [Amps] issue with AL-1200 output -UPDATE NUMBER 2-

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Subject: Re: [Amps] issue with AL-1200 output -UPDATE NUMBER 2-
From: "Jim Thomson" <>
Date: Tue, 27 Jun 2017 06:04:45 -0700
List-post: <>
Date: Mon, 26 Jun 2017 21:19:02 -0400
From: Steve Bookout <>
Subject: Re: [Amps] issue with AL-1200 output -UPDATE NUMBER 2-

<Hello Merv,

<I understand the concept, I just didn't know of any amp mfgr doing that.

<That one is toast.  I could easily make one out of some copper I have 
<and re-install with a 'just slightly' closer spacing than the plates.

<Or, I may just take my chances like I've done for many years.  I do know 
<people who DO arc their caps with regularity; I am not one of those guys.

<73 de Steve, NR4M

##  A spark gap across the tune cap is an excellent idea..and done all the 
Another place to wire in a  spark gap is across the load cap.  I use vac tune +
load caps.   An adjustable spark gap is cheap insurance....esp for a load cap. 
The adjustable  spark gap can be fabricated similar to what vibroplex uses for
adjustable contacts.  One threaded  machine screw, like a 6-32  or  8-32...with
tip ground to a sharp point.   Then a mating, non adjustable,  ground down, 2nd
machine screw.  Then some locking nuts etc, so when adjusted, tweaked,  to the
desired gap, its then locked down. 

##  in the case of the vac load cap, the spark gap is set such that it fires 
well below the
peak V rating of the vac load cap... but higher than the highest expected
say  3:1    or  4:1.  The idea here is that with the Array solutions power 
wattmeter or similar being used, with their adjustable swr shut down circuitry,
the spark gap is set higher  than the high swr shut down threshold.   

##  So in normal operation, the high swr threshold circuitry will shut things 
down asap. 
Call that a  ..soft fault.    In the case of a ..hard fault, like a solid short 
on the output coax,
or a wide open on the output coax, both resulting in infinite high swr, the arc 
gap across the
load cap will ensure a brick wall shut down.... for the case of wide open coax. 
  If coax shorted,
the Peak V across the load cap drops to zero anyway, along with the voltages 
across the tank coil,
band switch  +  tune cap. 

##  If excess drive applied, high power spikes from xcvr, mis tuning, load 
control set too low... IE:
more meshed, etc, etc, then the C1 tune cap is also protected in a similar 
fashion with its own adjustable
spark gap. In the case of the adjustable spark gap across any C1 tune cap, it 
has to be done so you are 
not adding additional  stray C in parallel with the C1 cap.   Hence the pair of 
pointed machine screws..facing each other. 

Jim   VE7RF 
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