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Re: [Amps] SCR to adjust 240v to 200v

To: Jim Durham <>
Subject: Re: [Amps] SCR to adjust 240v to 200v
From: Michael Clarson <>
Date: Fri, 12 Aug 2016 15:41:33 -0400
List-post: <">>
Jim: Motorola did something like you describe in their "MOTRAC" series base
stations (beige cabinets) in the 1960s and 70s. These were 250-350 watt
output stations using a pair of 8560s as finals. They regulated B+ with
SCRs in the transformer primary. All done at 60 Hz and never had any RFI
issues from these supplies. I do not have any manuals. Later versions of
these stations used constant voltage transformers. Good luck finding a
solution. --73, Mike, wv2zow

On Fri, Aug 12, 2016 at 1:07 PM, Jim Durham <> wrote:

> Hello all,
> This is my first posting, so Howdy..
> I have a Henry 2k-2 (modified to take 3-500Zs).  After I bought it, some
> years back, I fired it up and tube filaments were very bright and HV was
> high.
> 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.
> 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?
> Anyone have any experience with this?
> Thanks and 73,
> Jim, W2XO
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