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Re: [Amps] Grid Protection Circuit Ideas

To: Allen Jones <>
Subject: Re: [Amps] Grid Protection Circuit Ideas
From: R L Measures <>
Date: Mon, 26 Jun 2006 11:17:12 -0700
List-post: <>
On Jun 26, 2006, at 8:48 AM, Allen Jones wrote:

> I have a Heatkit SB-230 amp and would like to add
> protection for the grid.  I'm not an engineer but it
> looks like a simple transistor switch with a latching
> relay will not suffice as it would be difficult to
> develop the 0.6 to 0.7 VDC needed with the low amount
> of grid current that normally flows in the metering
> circuit.  Eimac specs the tube at 30ma max.

  The spec is 5w max.
> I was told to use a circuit similar to the one in the
> Ameritron AL-800 or 1200 which uses an op amp.  The
> manuals are available on the Ameritron site but do not
> contain schematics.  Any suggestions or assistance
> will be much appreciated.

Grid fusing can be accomplished by putting a 20 to 39-ohm, 1/4w  
carbon film R - or a fast-acting 1/10a fuse - in series with the grid- 
I meter shunt.   Additionally, a 30v to 50v transient V suppressor  
should be connected across the fusing element, back to belly 3a  
diodes should be paralleled with the meter movement, and a glitch R  
added in series with the HV+ lead.
   If it was my amp I would add a VHF suppressor to improve stability.
> Allen, W9DZ
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R L MEASURES, AG6K. 805-386-3734

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