Reference discussion concerning "SCR to adjust 240v to 200v":
There is a good application note available on the Littelfuse website concerning
phase control; google: littelfuse phase control ; should take you right
to it (their Application Note is AN1003). They show a number of circuits, and
are not specific to their products. Some comments from experience: (1) be
sure control the effective voltage by when you turn ON the conduction, letting
it turn itself off at the zero-crossing. (the application note shows this)
You do NOT not want to turn off the current when there is still a voltage
across the control device; you will generate much bigger spikes. (2) You will
get spikes anyway. 130 VAC MOVs across the load (in this case, this will be
the primary of the transformer) are helpful for this. A MOV across the input
to your circuit is also a good idea, it will help prevent spikes being sent out
on the power line. High voltage caps of about .01 uF in parallel with the MOVs
also help.
You didn't mention whether you already have a 3KVA Variac (or Powerstat). If
you don't already, such a device will be heavy and expensive.
Good luck and 73,
Gene May WB8WKU
________________________________
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Sent: Monday, August 15, 2016 2:00 PM
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Subject: Amps Digest, Vol 164, Issue 8
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Today's Topics:
1. Re: Ldmos heat spreaders (Tom Thompson)
2. SCR to adjust 240v to 200v (Jim Thomson)
3. Re: SCR to adjust 240v to 200v (Jim Brown)
4. Re: SCR to adjust 240v to 200v (Michael Clarson)
5. Re: SCR to adjust 240v to 200v (Jim Brown)
6. Re: SCR to adjust 240v to 200v (Jim Brown)
7. AL-82 VS Acom 1000 (Morgan Bailey, II)
----------------------------------------------------------------------
Message: 1
Date: Mon, 15 Aug 2016 08:06:25 -0600
From: Tom Thompson <w0ivj@tomthompson.com>
To: Ian Swain <insane.swain@gmail.com>, amps@contesting.com
Subject: Re: [Amps] Ldmos heat spreaders
Message-ID: <0b766cff-f30a-5dde-67c6-2bf1949820a0@tomthompson.com>
Content-Type: text/plain; charset=windows-1252; format=flowed
Hi Ian,
http://www.communication-concepts.com/heat-sinks/
73, Tom W0IVJ
On 8/12/2016 1:52 PM, Ian Swain wrote:
> Hi guys I'm building my first ldmos amp with a blf188xr and can't find a
> nice think slab of copper for a heat spreader
>
> I've only found up to 6mm think would this be okay ? Or could I get away
> with 2 layers to get 12 mm with heat transfer paste ?
>
> Any other zl stations or vk found a good copper source ?
>
> 73 de zl2ias
> All the best
> _______________________________________________
> Amps mailing list
> Amps@contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
>
>
------------------------------
Message: 2
Date: Mon, 15 Aug 2016 07:42:24 -0700
From: "Jim Thomson" <jim.thom@telus.net>
To: <amps@contesting.com>
Subject: [Amps] SCR to adjust 240v to 200v
Message-ID: <CABBA786E9054A12A497006594FEB2A9@JimPC>
Content-Type: text/plain; charset="iso-8859-1"
Date: Sat, 13 Aug 2016 11:11:33 -0400
From: Jim Durham <jimdur@gmail.com>
To: amps@contesting.com
Subject: Re: [Amps] SCR to adjust 240v to 200v
Thank you, Boye (OZ7C) and the others that replied. I think I did not
explain my project clearly.
First of all, yes, I know about buck transformers. I am using a Variac,
which does the same thing and also allows me to adjust the input AC
voltage. The Henry 2K has the filament voltage supplied from a winding
on the plate transformer, so, with the Variac, I can adjust the input AC
voltage to give about 9.8 volts for the filaments, which is ideal and
produces 3000 volts for the plates.
A large buck transformer or Variac requires an external box, which is
what I am using now. They won't fit in the amplifier without seriously
hacking up the cabinet. I don't want to do that.
So, I was just asking if anyone on Amps had tried using an SCR to
control a large choke-input power supply ? That sounds attractive and
would fit in the cabinet, but also might damage the power supply choke
by applying non-sinusoidal power (the 2K-2 has a choke input power
supply). That was my question.
Thanks to all, I should have explained more clearly what I was asking.
73 de Jim, W2XO
## still another method is to use a small variac on the primary of the buck
xfmr.
Sec of buck xfmr goes in series with one leg of the 240 line. Then u can
easily
dial up the exact buck voltage you want. Forget the scr, not gonna work.
Or use a buck xfmr with several taps on both the pri and sec.
Jim VE7RF
------------------------------
Message: 3
Date: Mon, 15 Aug 2016 08:34:33 -0700
From: Jim Brown <jim@audiosystemsgroup.com>
To: amps@contesting.com
Subject: Re: [Amps] SCR to adjust 240v to 200v
Message-ID:
<c06f8976-f54d-fd6a-ab2b-2830b80f32d6@audiosystemsgroup.com>
Content-Type: text/plain; charset=windows-1252; format=flowed
On Fri,8/12/2016 12:41 PM, Michael Clarson wrote:
> All done at 60 Hz and never had any RFI
> issues from these supplies.
I'm sure that Motorola carefully designed so that there was no RFI at
VHF/UHF. But this sort of circuitry is FAR more likely to generate trash
at MF and HF. Bottom line -- it's not necessarily a slam dunk. By
contrast, the boost/buck transformer IS a slam dunk, and guaranteed not
to add noise.
73, Jim K9YC
------------------------------
Message: 4
Date: Mon, 15 Aug 2016 12:12:53 -0400
From: Michael Clarson <wv2zow@gmail.com>
To: jim@audiosystemsgroup.com
Cc: Amps Amps <amps@contesting.com>
Subject: Re: [Amps] SCR to adjust 240v to 200v
Message-ID:
<CAFx0t24BfHbtCq+oSq+UNmmkeyRUsq2ETcEkhpXZ3wwH9ToKVQ@mail.gmail.com>
Content-Type: text/plain; charset=UTF-8
Yes, Jim. The Motorolas were all VHF/UHF. They did make them to work as low
as 25 MHz, which was just barely HF. I never liked fixing those supplies.
Lightning was always taking out some of the semiconductors. I'm going to
try to find a manual and see exactly how they did it. --73, Mike, WV2ZOW
On Mon, Aug 15, 2016 at 11:34 AM, Jim Brown <jim@audiosystemsgroup.com>
wrote:
> On Fri,8/12/2016 12:41 PM, Michael Clarson wrote:
>
>> All done at 60 Hz and never had any RFI
>> issues from these supplies.
>>
>
> I'm sure that Motorola carefully designed so that there was no RFI at
> VHF/UHF. But this sort of circuitry is FAR more likely to generate trash at
> MF and HF. Bottom line -- it's not necessarily a slam dunk. By contrast,
> the boost/buck transformer IS a slam dunk, and guaranteed not to add noise.
>
> 73, Jim K9YC
>
>
> _______________________________________________
> Amps mailing list
> Amps@contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
>
------------------------------
Message: 5
Date: Mon, 15 Aug 2016 09:21:48 -0700
From: Jim Brown <jim@audiosystemsgroup.com>
To: amps@contesting.com
Subject: Re: [Amps] SCR to adjust 240v to 200v
Message-ID:
<d23107f7-b1f4-34bd-5bfb-93d08fa50d9e@audiosystemsgroup.com>
Content-Type: text/plain; charset=windows-1252; format=flowed
On Sat,8/13/2016 8:11 AM, Jim Durham wrote:
> I am using a Variac, which does the same thing and also allows me to
> adjust the input AC voltage.
What it does that is the same is that it adjusts the primary voltage.
But it is VERY different from a boost/buck transformer, because it must
be rated for the full VA of the load.
A boost/buck transformer requires that the primary be rated for the line
voltage, but a much smaller current. Only the secondary must be rated
for the full load current. The result is that a good boost/buck
transformer is a much smaller and lower cost solution. All of them that
I have seen are multi-tapped and are clearly marked with voltage and
current ratings and their turns ratios, so it's almost trivially easy
to choose one and hook it up.
73, Jim K9YC
------------------------------
Message: 6
Date: Mon, 15 Aug 2016 09:30:25 -0700
From: Jim Brown <jim@audiosystemsgroup.com>
Cc: Amps Amps <amps@contesting.com>
Subject: Re: [Amps] SCR to adjust 240v to 200v
Message-ID:
<686796c3-9e89-9125-a9de-6ef8727b7ebe@audiosystemsgroup.com>
Content-Type: text/plain; charset=utf-8; format=flowed
No surprise. About 40 years ago, I had a job maintaining and
troubleshooting a wide range of installed systems -- audio, video,
security, etc. One was a simple intercom in an apartment complex that
used SCRs for something -- don't even remember what -- but they had a
very low voltage rating, and were always failing from voltage induced on
system wiring. Ten Tec made a similar error with too-low voltage ratings
on the discrete semiconductors used in the keying logic of their
otherwise very nice Titan 425 amp. In both cases, there were higher
voltage rated parts in the same series, but I've got a feeling that, as
so often happens, the bean counters subbed the lower voltage parts to
save pennies.
73, Jim K9YC
On Mon,8/15/2016 9:12 AM, Michael Clarson wrote:
> Lightning was always taking out some of the semiconductors. I'm going
> to try to find a manual and see exactly how they did it. -
------------------------------
Message: 7
Date: Mon, 15 Aug 2016 11:34:38 -0500
From: "Morgan Bailey, II" <mcb2179@gmail.com>
To: amps@contesting.com
Subject: [Amps] AL-82 VS Acom 1000
Message-ID:
<CADa2mviGqCD4jC1LcGB5b3xvRTW9_CmeBDVMsPfGttV6mO_3jg@mail.gmail.com>
Content-Type: text/plain; charset=UTF-8
Hello everyone
I have a dilemma on my hands. I currently have the opportunity to purchase
a pre-mfj AL-82 with a Dahl transformer in pristine condition for a very
low price. I also have been looking at the ACOM line and I like the 1000.
Other than the fact that there is an output difference between the amps, is
the extra money for the Acom worth it? The majority of my operating is cw
contesting, and I will be driving the amp with a K3. I like the fact that
the Acom is QSK capable and is very quiet, but that alone isn't enough
justification for me to spend $1200+ over the cost of the AL-82. One of
the attractive things about the AL-82 is that it is simple enough that I
know I can repair almost anything that were to happen to it, and the tubes
are cheap. This is not the case with the Acom. Overall I really like Acom
better, but there is such a large price difference between the two amps
that I'm having trouble deciding whether the extra money is worth it for
the Acom.
Thoughts?
73, Morgan, NS0R.
------------------------------
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