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[AMPS] Step Start for Ameritron AL-80A

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Subject: [AMPS] Step Start for Ameritron AL-80A
From: (Rich Measures)
Date: Tue, 17 Mar 98 03:18:43 -0800
>Mike Willis wrote:
>>The relay is across the transformer primary, an AC one which activates
>>after about
>>a second. So far so good.
>>For the EHT short problem, I have a resistor in series with the EHT. 
>The problem I was thinking of was when you get a trouble in the
>transformer or bridge or HV caps; then the mains limiting resistors
>don't get switched out.
>In message <19980316102421.AAC10088@[]>, Rich Measures
><> writes
>>> 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 you can't mistake the fault indication, but I find it easier to
>replace a fuse :-)
If a circuit fault blows the mains fuses, replacing the fuses will not 
fix the fault, and will result in blowing yet another pair of fuses.  If 
there is a circuit fault, the fix is going to require plugging in one's 
soldering iron.  .  Fuses for a TL-922 go for $15 each from Kenwood.  7w 
resistors go for around $1.50 each.  
>>>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. 
>Indeed - I was thinking of the difference between a commercial amp with
>one transformer for all supplies and home brew system where the
>auxilliary supplies are often separate.

There is virtually no difference between the values needed for 
stepstarting a single transformer and stepstarting two transformers, 
providing that the total VA ratings are similar.  
>>>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. 
>True, but it's only pennies.
A fixed timer costs more than the stepstart circuit in Figure 1, which 
uses the existing hv filter as the timing capacitor.  


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

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