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The Dynaco Tube Audio Forum

Dedicated to the restoration and preservation of all original Dynaco tube audio equipment - Customer support for Tubes4hifi VTA tube amp and preamp kits and all Dynakitparts.com products


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    Variac's on sale right now at Circuit Specialists in AZ

    Bob Latino
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    • Post n°1

    Variac's on sale right now at Circuit Specialists in AZ Empty Variac's on sale right now at Circuit Specialists in AZ

    Post by Bob Latino Wed Dec 28, 2016 10:25 am

    I have a few customers that live in areas of the USA that have incoming AC voltages above 122 VAC. Running a tube amp off AC voltages higher than normal will raise the amp's internal AC and DC voltages and reduce tube life (especially the rectifier tube). Circuit Specialists in AZ right now are having a sale on their variacs. Yes - The variacs are made in China but they seem to work well from customer's reports. Right now the 5 amp model which would be fine for the VTA ST-70 or ST-120 is $55 with FREE SHIPPING. The larger 20 amp model which would be fine for TWO M-125's is now at $104 and also with free shipping.

    5 amp variac at Circuit Specialists

    20 amp variac at Circuit Specialists

    Bob
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    • Post n°2

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    Post by eickmewg Wed Dec 28, 2016 6:10 pm

    I have the 5 amp model. I had my power strip/surge protector plugged into this variac which was plugged into a wall socket. I noticed that the "grounded" light was not lit on the power strip. Using a three-light socket tester it turned out that the variac had the hot and neutral lines reversed. This can be easily corrected with a little wiring change. Maybe mine was unusual (I hope so) but if you get one of these it would be worth checking this out before putting it into service. After the wiring change it was grounded properly and worked as it should.
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    Variac's on sale right now at Circuit Specialists in AZ Empty Re: Variac's on sale right now at Circuit Specialists in AZ

    Post by GlacierJohn Wed Dec 28, 2016 8:27 pm

    Thanks for the heads up; do you think the 5 watt model could handle two MK IIIs and a Super Pas 3 pre amp?
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    Post by Bob Latino Wed Dec 28, 2016 8:47 pm

    GlacierJohn wrote:Thanks for the heads up; do you think the 5 watt model could handle two MK IIIs and a Super Pas 3 pre amp?

    I think running 3 pieces off one variac, you should probably use the 20 amp model ..

    Bob
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    • Post n°5

    Variac's on sale right now at Circuit Specialists in AZ Empty Re: Variac's on sale right now at Circuit Specialists in AZ

    Post by Dogstar Wed Dec 28, 2016 8:59 pm

    If this is the same source for Variacs that you plugged awhile ago then i agree that even though they are made in China the one I got is very well made and performs quite well. I use it on

    At my workbench. I had not checked the hot and neutral lines but will now. I got the 20 amp model but think I will spring for a few of the 5 amp models for my family room and bedroom systems.
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    • Post n°6

    Variac's on sale right now at Circuit Specialists in AZ Empty Re: Variac's on sale right now at Circuit Specialists in AZ

    Post by Bob Latino Wed Dec 28, 2016 9:18 pm

    Dogstar wrote:If this is the same source for Variacs that you plugged awhile ago then i agree that even though they are made in China the one I got is very well made and performs quite well.

    Dogstar I didn't mean to "plug" them and I honestly have never used this variac. I was just passing on info from a number of customers that did use them and found them to work well. The 5 amp unit is normally about $65 - $75 shipped so $55 shipped is a good price. This is probably an "after Christmas sale" ... Look for the price to go back up in a few weeks ..

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    • Post n°7

    Variac's on sale right now at Circuit Specialists in AZ Empty Re: Variac's on sale right now at Circuit Specialists in AZ

    Post by Dogstar Wed Dec 28, 2016 10:25 pm

    Bob Latino wrote:
    Dogstar wrote:If this is the same source for Variacs that you plugged awhile ago then i agree that even though they are made in China the one I got is very well made and performs quite well.

    Dogstar I didn't mean to "plug" them and I honestly have never used this variac. I was just passing on info from a number of customers that did use them and found them to work well. The 5 amp unit is normally about $65 - $75 shipped so $55 shipped is a good price. This is probably an "after Christmas sale" ... Look for the price to go back up in a few weeks ..

    Bob

    Bob...I wrote my response in a hurry. Maybe 'plug' was the wrong word to use. I bought mine awhile ago based on your recommendation or suggestion, which are probably the better words to use, and I am happy with the performance so far. Though now I'm curious about the product. I think if I have time this weekend I will open it up to see what it looks like on the inside. If it looks like the Sophia I am going to be concerned.


    Last edited by Dogstar on Thu Dec 29, 2016 8:54 am; edited 1 time in total
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    • Post n°8

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    Post by pedrocols Wed Dec 28, 2016 11:42 pm

    I have been using one of the 20 amps for maybe a year with zero issues so far...
    Variac's on sale right now at Circuit Specialists in AZ IMG_0720_zps7d8qapxt
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    Post by eickmewg Thu Dec 29, 2016 7:25 am

    After the issues with my 5 amp "Variac," I decided to fabricate a bucking transformer. I used a 7 amp transformer and this has now pushed the "Variac" to the storage room. It was about half the price of the 5 amp "Variac" in parts. I don't have to worry about inadvertently changing voltage. I can still use it to bring up old equipment but it is out of continuous service.
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    • Post n°10

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    Post by Peter W. Thu Dec 29, 2016 12:05 pm

    Dogstar wrote: >>SNIPPAGE<< I think if I have time this weekend I will open it up to see what it looks like on the inside. If it looks like the Sophia I am going to be concerned.

    Attached are some pictures of the brush assembly and windings from several US-made products in current production. This is where there will be the most noticeable differences, if any.

    Powerstat: http://www.recycledgoods.com/media/catalog/product/cache/1/image/1000x/af097278c5db4767b0fe9bb92fe21690/s/u/superior-electric-10c-powerstat-variable-transformer-range-.3-to-1-vac-low-to-126-to-127.6-vac-high-1.39.jpg

    Small General Radio (Variac): http://www.carbonbrush.com/variac3.jpg

    Larger General Radio (Variac): https://s129.photobucket.com/user/tbbboj/media/variacbrush-v10.jpg.html

    Staco: http://thumbs3.picclick.com/d/l400/pict/141697681846_/NEW-NO-BOX-Staco-Type-251-Variable-Autotransformer.jpg

    And, to be fair, the Chinese Source in question: http://www.swdigital.org/fudmeister/main.php?g2_itemId=443

    Which does not look half-bad in the pictures other than the fact that the power-cord is secured with elephant snot, and the switch connections are soldered, not push-on. You pays your money, you takes your choice.

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    Post by wgallupe Thu Dec 29, 2016 1:13 pm

    I've been using the 20 amp model for the past couple years. Its knocking down my house voltage from 123VAC to 117. Every time I check it with a multimeter its spot on the 117 I originally set it to. I suppose that also means my local utility provides a constant voltage.

    With that said I recently came across a thread over at Audiokarma where a guy tested his Chinese variac with a 3 light circuit tester and found it to be wired wrong. Since I was in the middle of my Mark III build and the variac was just sitting there I tested it. Low and behold mine was also wired wrong. I opened it up and swapped the load and neutral wires. It tests good now.

    I now have my Mark III mono blocks and my SP13 preamp plugged into it. No issues AND a faint but pesky 60 cycle hum I always had is now gone!  

    My recommendation is check your variacs for correct wiring. The 3 light testers are cheap and available everywhere.

    Audiokarma link: http://www.audiokarma.org/forums/index.php?threads/variac-grounding.745140/
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    Post by eickmewg Thu Dec 29, 2016 4:41 pm

    Yeppers, that was me over on Audiokarma. So now we know at least two of these "Variacs" were not wired properly. Cause for concern?? I second the recommendation to get a three-light circuit tester. Mine cost a lofty $8.00.
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    Post by monkuboy Thu Dec 29, 2016 4:58 pm

    I have the 20 amp Variac on the way, should arrive tomorrow. I saw Bob's post yesterday and thought the price was reasonable enough to try it out. The suggestions to check the actual voltage with a MM and also test to make sure it is wired properly are much appreciated!
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    Post by wgallupe Fri Dec 30, 2016 3:58 pm

    eickmewg wrote:Yeppers, that was me over on Audiokarma.  So now we know at least two of these "Variacs" were not wired properly.  Cause for concern??  I second the recommendation to get a three-light circuit tester.  Mine cost a lofty $8.00.

    Well, thanks for your posts over there and here! You led me down a good path. Love these forums. So much info/knowledge to share...
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    Post by wgallupe Fri Dec 30, 2016 4:13 pm

    monkuboy wrote:The suggestions to check the actual voltage with a MM and also test to make sure it is wired properly are much appreciated!

    You're welcome  Very Happy  The gauge that comes mounted on the unit is not accurate at all. I reads several volts lower than actual. Rolling Eyes
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    Post by monkuboy Sat Dec 31, 2016 2:19 pm

    I tried out the Variac just now.

    The wall outlet measurement using a Fluke 115 MM shows 120.5V-120.6V. Then I plugged in the Variac. The voltage adjustment dial is way off. At 120V on the dial, I measured 134.4V! I had to turn it down to around 105V to get it to output 120V. Once set, I noticed the voltage fluctuated a few tenths of a volt, like +/- .2V. I also verified the Variac is wired correctly.

    I have been using an Emotiva CMX-2 power conditioner. With 120V input, the output measures 118.3V-118.4V. So this device actually decreases the incoming voltage.

    I'm thinking of returning the Variac given how the dial is so far off that it then calls into question the reliability of the unit overall. I'm also wondering what is up with the CMX-2. I have two of them and both show the same output voltage when the incoming voltage is 120V.

    Any comments? Also, is that 118V rather than 120V doing any harm to anything?
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    Post by Peter W. Sat Dec 31, 2016 3:00 pm

    Most, but not all line conditioners keep output voltages at/below 120V using a voltage regulating circuit that is NOT a ferro-resonant constant-voltage transformer. Most will do so over a pretty wide range of input voltages, typically about 87V to about 145V or so.

    118 V is fine. No problems.

    There is probably a small pot inside the conditioner that would allow you to adjust this, but writing for myself, I would be happy with 118V.
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    Post by monkuboy Sat Dec 31, 2016 3:08 pm

    Peter W. wrote:Most, but not all line conditioners keep output voltages at/below 120V using a voltage regulating circuit that is NOT a ferro-resonant constant-voltage transformer. Most will do so over a pretty wide range of input voltages, typically about 87V to about 145V or so.

    118 V is fine. No problems.

    There is probably a small pot inside the conditioner that would allow you to adjust this, but writing for myself, I would be happy with 118V.

    Thanks, Peter. So if that line conditioner keeps the voltage below 120V, it seems like there wouldn't be a need for a Variac?

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    Post by Bob Latino Sat Dec 31, 2016 3:30 pm

    monkuboy wrote:
    Peter W. wrote:Most, but not all line conditioners keep output voltages at/below 120V using a voltage regulating circuit that is NOT a ferro-resonant constant-voltage transformer. Most will do so over a pretty wide range of input voltages, typically about 87V to about 145V or so.

    118 V is fine. No problems.

    There is probably a small pot inside the conditioner that would allow you to adjust this, but writing for myself, I would be happy with 118V.

    Thanks, Peter.  So if that line conditioner keeps the voltage below 120V, it seems like there wouldn't be a need for a Variac?


    Some line conditioners alter the AC voltage but do not put out AC in the form of a true sine wave. Tube amps will "choke" if not fed AC in the form of a true sine wave. A variac will always put out AC as a true sine wave.

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    Post by monkuboy Sat Dec 31, 2016 4:35 pm

    Bob Latino wrote:
    monkuboy wrote:
    Peter W. wrote:Most, but not all line conditioners keep output voltages at/below 120V using a voltage regulating circuit that is NOT a ferro-resonant constant-voltage transformer. Most will do so over a pretty wide range of input voltages, typically about 87V to about 145V or so.

    118 V is fine. No problems.

    There is probably a small pot inside the conditioner that would allow you to adjust this, but writing for myself, I would be happy with 118V.

    Thanks, Peter.  So if that line conditioner keeps the voltage below 120V, it seems like there wouldn't be a need for a Variac?


    Some line conditioners alter the AC voltage but do not put out AC in the form of a true sine wave. Tube amps will "choke" if not fed AC in the form of a true sine wave. A variac will always put out AC as a true sine wave.

    Bob

    Thanks, Bob. When you say the amp may "choke," what do you mean by that, or what would be the signs?
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    Post by Bob Latino Sat Dec 31, 2016 4:39 pm

    Shortened tube life .. Especially the rectifier tube ..

    Bob
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    Post by monkuboy Sat Dec 31, 2016 4:41 pm

    Bob Latino wrote:Shortened tube life .. Especially the rectifier tube ..

    Bob

    Thank you, and happy New Year to you, as well as the rest of the forum members.

    Getting the ST-120 made it a very good 2016 for me!
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    Post by Peter W. Sat Dec 31, 2016 5:00 pm

    I think we need to clarify a term-of-art. An audio grade line conditioner is designed to remove artifacts from "dirty" AC lines. So, yes it will put out a true sine wave at a fixed voltage. These are not cheap. Tripp-Lite makes some good units amongst others.
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    • Post n°24

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    Post by pedrocols Sat Dec 31, 2016 6:03 pm

    Peter W. wrote:I think we need to clarify a term-of-art. An audio grade line conditioner is designed to remove artifacts from "dirty" AC lines.  So, yes it will put out a true sine wave at a fixed voltage. These are not cheap. Tripp-Lite makes some good units amongst  others.
    So basically if the line is clean the line conditioner is not needed and a waste of $$. I am not an electrician or engineer but how do you go about knowing or determined the AC lines are contaminated with artifacts?
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    Post by monkuboy Sat Dec 31, 2016 6:15 pm

    Another question here... I plugged in the Variac and then plugged the ST-120 into the Variac. When I turned on the ST-120, the voltage in the Variac dropped from 120.0V to 119.3V. Isn't the voltage supposed to remain the same? Same thing with trying the TV - there was a slight drop in voltage when turning it on, and an even slighter drop when just plugging in the TV without turning it on (it was in a ready state with the LED light on showing it was plugged in). Shouldn't the Variac keep the voltage constant?
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