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[AMPS] Step Start for Ameritron AL-80A

To: <>
Subject: [AMPS] Step Start for Ameritron AL-80A
From: (Rich Measures)
Date: Mon, 16 Mar 98 02:26:22 -0800
>In message <19980314202033.AAA7609@[]>, Rich Measures
><> writes
>>The circuit shown in Figure 1 at:  
>>is simple, uses a pair of inrush resistors so that it works on 120v and 
>>240v, and can be powered by the AL-80's 12vdc (?) supply.  The timing 
>>element is the hv supply filter capacitors.  When the caps. are 2/3 
>>charged, the relay closes.  For an AL-80 a pair of 7w c. 25 ohm resistors 
>>should work satisfactorily.  
>>later, Jack
>You might consider using current limiting resistors with a higher
>resistance and power rating, especially where you have a separate HV

The resistors w-rating is chosen according to the size of the amplifier.  
25 ohmers limit the inrush current to roughly less than 8A.  

> If there is a fault which draws high primary current and
>stops the HV output rising to the value that shorts out the resistors,
>they sit there with most of your line voltage across them until they go

That is the idea.  The resistors act as fuses in the event of a major 
circuit fault. If all's well, the 7w resistors barely get warm during the 
c. 1 second step-start.  

>I guess it's more difficult with a single transformer as you need
>to let the auxilliary supplies build up to operate the relay.
-  Two or more transformers act like a single transformer when the 
primaries are in parallel. 
>Having suffered once, I now use a fixed timer which gives a few seconds
>delay - if there's a fault then the line fuse blows.
A fixed timer changes only the capital investment. 


R. L. Measures, 805-386-3734, AG6K   

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