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To Variac or not to Variac.....




 
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February 22, 2018, 05:48:32 AM *
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Author Topic: To Variac or not to Variac.....  (Read 289 times)
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k3msb
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« on: February 13, 2018, 12:28:08 PM »

Being desirous of taking better care of my vintage gear, and having observed that my line voltage can be 10+ volts over when the radios were designed for,  I was wondering what folks are using to address this.

I know I can use a filament transformer to buck the voltage, or use a variac,  and Iím interested in what folks are actually using and issues theyíve had with either way.  Other solutions?

I know from my work on my Valiant my LV can be 30V+ different depending upon the line voltage.   Even using dropping resistors (with or without solid state rectifier replacements), the higher line voltage will stress the (pricey to replace/rewind) transformers.

Since I have a pair of nice 20A variacs in the pile, Iím tending to go with that solution.

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73 Mark K3MSB
York, PA
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« Reply #1 on: February 13, 2018, 12:45:08 PM »

I use a Variac, it's a honker at 20A, and it powers a "1950s Voltage" outlet strip that all the vintage gear is plugged in to. I was fortunate to have found an A.C. line voltage meter that also plugs in there so I can make sure the supply stays in the right decade.
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WD4DMZ
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« Reply #2 on: February 13, 2018, 12:49:34 PM »

Currently, I'm using a variac on a recently acquired Viking Ranger 2. My local line voltage can exceed 120 VAC and I want to keep this xmitter in good health. The R2 tunes up just fine with good audio as low as 110 VAC.

The variac is a NOS industrial GE rated at 10 amps and not very large. I have 15 amp units as well but the R2 uses under 3 amps so the 10 amp variac is more than adequate.

So, for this particular unit I will keep it on the variac.

Rich
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WD4DMZ
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« Reply #3 on: February 13, 2018, 01:03:39 PM »

In a previous thread someone suggested I use a Kil A Watt meter to monitor the voltage and current to see if anything odd is occurring. It is digital and reacts quickly. Also reads amps, watts, VARS and usage. Even totals your energy cost if you put in your local utility rate. Amazon has them under $50. I had a pair of them I used in experiments at school before I retired.

I really prefer analog meters over digital for the long run because they do not jump around. Over the years I have acquired quite a few old voltmeters, some industrial/utility grade. They look really cool but take up too much space.

All in all, the KAW is a good investment and a great tool if you are looking for such a gadget.

Rich

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Patrick J. / KD5OEI
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« Reply #4 on: February 14, 2018, 02:17:09 AM »

How about a bucking transformer of 10V@ whatever amps. Just knock a good 10V off the line.

Very inexpensive, there are many 12.6VCT 1-5A transformers around, as well as transformers to be salvaged from old solid state stuff, even car battery chargers almost free. The center tap if available might be useful for summer when all the a/c units drag the voltage down from 125 to 120, etc.

If adjustment's wanted, a small variac can control a large current this way so that a 10-20V 5A transformer secondary bucking the line can be powered with a 1A variac on the primary of the transformer.
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w4bfs
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« Reply #5 on: February 14, 2018, 02:58:16 AM »

In a previous thread someone suggested I use a Kil A Watt meter to monitor the voltage and current to see if anything odd is occurring. It is digital and reacts quickly. Also reads amps, watts, VARS and usage. Even totals your energy cost if you put in your local utility rate. Amazon has them under $50. I had a pair of them I used in experiments at school before I retired.

I really prefer analog meters over digital for the long run because they do not jump around. Over the years I have acquired quite a few old voltmeters, some industrial/utility grade. They look really cool but take up too much space.

All in all, the KAW is a good investment and a great tool if you are looking for such a gadget.

Rich



nice tip Rich .... found one on Ebay for $20 new .... ordered one to see  Smiley  Smiley
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MikeKE0ZUinkcmo
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« Reply #6 on: February 14, 2018, 07:12:01 AM »

I have a couple Variacs, a small 3VA and a 15VA, and I seldom use either.  I also have a Kill-A-Watt unit.  it's easy to use and prevented damage on a couple occasions.  

The issue is to
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Closely, watch the Watt meter, it should peak for a second or two, then start displaying lower readings, and continue going down for the next several seconds.  It will stabilize, and slowly increase across the next 30 seconds or so, approaching it's normal power consumption leve

Mike

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WA2ROC
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« Reply #7 on: February 14, 2018, 07:20:35 AM »

I use a 10 amp 7.5 volt filament transformer set up in the buck configuration for my Viking II and SX-101.  It cuts the average line voltage down to 112 volts, give or take a few volts.  An inline voltmeter shows what's applied to the radios.

I use a 10 amp variac on the other station, a Heath Apache, Mohawk, Marauder, Collins KWM2-A and a few other items, setting output voltage to about 115 volts. I keep a Kill-A-Watt on the variac output to set it to the desired voltage.   

Keep in mind I rarely use more than one "pair" of transmitter/receiver at a time. 

Each works like a champ. 
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Dick Pettit WA2ROC 
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