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[Amps] LK 500 problem

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Subject: [Amps] LK 500 problem
From: (2)
Date: Sun, 18 Aug 2002 10:09:49 -0700
>I have an Amp Supply LK 500 (2 3-500Z) that is starting to give me some 
>When I turn it on the Grid current goes negative and stays there.  

A grid/fil shorted tube will do this.  Lower VHF-Q parasitic suppressors 
will make the amp more stable -- but with the tradeoff of c. a 2% power 
out reduction at 29MHz.

>The plate current goes to about 200mA and also stays there.  The plate 
>looks OK.  It is an intermittent problem that sometimes goes away if I 
>power cycle the amp.
The filament double-helix expands when the tube is hot.  This can cause 
it to touch the grid cage when hot -- but not touch the grid cage when 
cold.  [photo of this phenomenon on p.15, Sept., 1990 *QST*.]

>I could use some help on debugging this.
>Thanks in advance
>Mike Walker VA3MW
>DX Cluster
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>Amps mailing list

-  R. L. Measures, a.k.a. Rich..., 805.386.3734,AG6K,  

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