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[Amps] SCR to adjust 240v to 200v

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Subject: [Amps] SCR to adjust 240v to 200v
From: "Jim Thomson" <>
Date: Sat, 13 Aug 2016 09:35:59 -0700
List-post: <">>
Date: Fri, 12 Aug 2016 15:00:00 -0400
From: Ron Youvan <>
To: amps <>
Subject: Re: [Amps] SCR to adjust 240v to 200v
   On 08/12/2016 01:07 PM, Jim Durham wrote:

/* snip */
> Talked to Henry. They asked me the plate transformer number, which they
> looked up and said "Oh, that's the 200v European transformer". So, I put
> a hefty variac on the 240v AC incoming and all is fine, except I'd like
> to ditch the variac and was wondering about if anyone on here had any
> wise words about using an SCR instead to back the AC voltage off.

   I would measure the incoming line Voltage RMS then I would locate a
used 240 Volt to (normal Voltage - 200) Volt transformer and buck the:
240 - 200 = 40 Volts at enough Amps with it.
   SCRs are headaches just waiting for you.

> My experience with big SCRs (TV studio lighting) was that they tend to
> put out a lot of RF hash.  I also wonder about how the choke and filter
> cap in the power supply would like non-sinusoidal AC waveform?
   Ron  KA4INM - Youvan's corollary:

##  I concur.  Use a  40 volt buck xfmr, but make sure u wire it up correctly,
so you buck 40 volts..and not add 40 volts !   SCRs are a pita, dont even go 
If you ever replace the plate xfmr, get a  real one, but you would also have to 
the low voltage stuff, like the fil xfmr, and any control xfmrs,  plus blower, 
etc, etc, etc. 

##  any  240-40 vac buck xfmr will have to be able to handle the full normal 
IE: the  40 vac sec side, that gets wired in series with the 240 vac, will have 
to handle
probably 15-20 amps.   So a 600-800 va  xfmr will be required.  Buy it  with 
lotsa taps
on either the  240 side...and  / or the sec side.  Then u can precisely control 
the voltage.
IE: pri taps at 235-240-245....and sec taps at 38-40-42 volts.

Jim   VE7RF   

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