Trying to rig a variac switch to slowing raise the voltage on an old tube amp

Discussion in 'Electrical Forum discussion & Blog' started by CanOfWorms, May 6, 2013.

  1. BobL43

    BobL43 DIY Senior Member

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    1,786
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    Long Island, NY
    Those new electrical parts made in China, especially those "wall warts" plug in transformers smell that way brand new. I guess they pre-burn them to make them smell that way or use recycled burnt plastic parts.

    I bought a nice toy recently; the Irrigation Caddy sprinkler control. I love it, but it came with one of those smelly wall warts. I wrote a review on it at Ama zon dot com the other day
  2. DonL

    DonL Out of the Trades

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    3,909
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    Houston, TX
    That smell is the Plastic and sometimes the Fish Oil used for the Transformer Insulation.


    It is nice that you take care of your Golf Cart and Caddy.

    I would provide Beer also.
  3. BobL43

    BobL43 DIY Senior Member

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    1,786
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    Long Island, NY
    My Caddy lives in my house and has his own IP address. His name is Pierre. When the grass needs to be cut, I tell him to mow zee lawn. Should I give him Dos Equis or Tecate, or Corona? I don't know any French beers. I do now; Google is my friend, http://www.ratebeer.com/country/france/72/
  4. leejosepho

    leejosepho DIY scratch-pad engineer

    This is actually similar to one of my first-ever threads here in Terry's forums. I had shortened a piece of heating wire while installing it in the floor of a small bathroom, then learned I could no longer feed it with 120 volts. Several folks here and one or two who are no longer here then began showing me all the different ways to control the voltage to that wire so it would never get more than 70 volts. During all of that is when and where I got my basic education about series and parallel...and I ultimately learned it is a very bad idea to shorten pre-made heating wire!

    You cannot draw white wire on a white background... ;)
  5. DonL

    DonL Out of the Trades

    Messages:
    3,909
    Location:
    Houston, TX

    I have used a roll of wire to get voltage drop, for testing. Lightbulbs are great also.

    Works good if you don't have a high power resistor available.

    LED bulbs don't work so well. Was that a LED Lightbulb. lol

    Red is not a good color to use for Neutral, Grey or Blue may have been better.

    I thought it was DC wiring for a moment.


    A fuse was not shown, but should be in line also, or you should not be playing with Dr. Watts On.
    Last edited: May 10, 2013
  6. BobL43

    BobL43 DIY Senior Member

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    Very true, you got me there. He should have wrapped it with white jpeg tape or put in a darker background. I thought everybody has white jpeg tape.
  7. leejosepho

    leejosepho DIY scratch-pad engineer

    Best chuckle I have had in a while! :)
  8. DonL

    DonL Out of the Trades

    Messages:
    3,909
    Location:
    Houston, TX

    Bob has all of the cool tools.

    I wonder why he does not share ?

    I want some jpeg and mpeg tape also.


    I wonder if BOB has it in Pink ?
    Last edited: May 11, 2013
  9. BobL43

    BobL43 DIY Senior Member

    Messages:
    1,786
    Location:
    Long Island, NY
    My mpeg tape worked great until I bought a new PC with Windows 8. All of a sudden, I had no CODECS to play mpegs. Yep, Windows 8 is a big improvement. I reinstalled an old (V9) of Nero to play those videos. Lots of freebies out there, and several CODEC suppliers, but I am comfy with Nero. Pink IS hot. I have some mpeg tape I would like to give her. Oh and now that you mentioned it, Cher is still hot too.

    My tool is old. No rust on it, and it works real well. Polishing it every so often keeps it nice and shiny.

    Just bought a new compression tool for coax cable fittings. Trying to get back to topic.

    Now we are WAY off topic.
    Last edited: May 11, 2013
  10. DonL

    DonL Out of the Trades

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    3,909
    Location:
    Houston, TX

    I was cheap and bought a compression tool from China.

    I could not see paying 3 times more for one, used at home on occasion.

    Now connectors, I buy the good ones. I like BNC over F, but the new F type are not to bad.


    Enjoy
  11. BobL43

    BobL43 DIY Senior Member

    Messages:
    1,786
    Location:
    Long Island, NY
    Ming was made in China too. Paid 22 bucks in the Amazon Jungle for it. I got the F59 connectors because the lightning supressors I bought have F connections on them. The tool came with dies for BNC and RCA compression fittings too. Its not the best, but once adjusted properly, is does the job correctly. I wrote a review on it in the jungle place.
  12. CanOfWorms

    CanOfWorms Member

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    174
    Location:
    New Jersey
    Hey guys. Thanks for the input. I actually did this about 5 mintues after I posted this but without the dimmer switch.

    Either way, I blame Bob for the green light.

    I don't know if the fixture was made to daisy-chain or not. It was a builder's basic from the supply house.

    I know that if I put speakers in parallel is cuts the resistence (ohm) in half. But I don't know how that would affect this situation.

    Everything worked out fine regardless.

    Rocket scientist, Thanks for the insult. I noticed you have a hard time with some parts of speach. Maybe that means you should stop typing or possibly even stop speaking English. If you don't know what I mean you should read through your posts. Wait... you wouldn't notice it since you typed it that way in the first place.

    Either way it works and I thought Bob wanted an update. Here is a video I posted when I got it working properly.
    Figuring out how to wire the speakers was a real b--ch. Not only did it require jumpers and dowloading an owner's manual, but also a photo enhancer... don't ask.
    Here's a video. I know I suck. You can make fun of me some more if you want. I don't mind if you don't mind my reaction.

    [video=youtube_share;Gjkto4fnt6s]http://youtu.be/Gjkto4fnt6s[/video]
  13. leejosepho

    leejosepho DIY scratch-pad engineer

    Me neither, or at least not for sure, but I believe that might be different since the amp output is determined beforehand where the typical AC lighting circuit is more of an as-needed or "on-demand" system. In other words, the amp circuit needs/wants/expects the load to match the supply where a lighting circuit does not care about the size of the load as long as the demand is not greater than it can handle...but I might be wrong about all of that!

    My Fender Bassman in the '60s was electronic, but other guys I knew would only ever play through tubes. Congrats on getting yours going.
  14. BobL43

    BobL43 DIY Senior Member

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    Oh man Can, you insulted my pal Don; now I won''t even kid around with you anymore here. I'm out. But Don and I DO understand how all this stuff works. By the way, your music video is fabulous and very professional. lol
  15. CanOfWorms

    CanOfWorms Member

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    174
    Location:
    New Jersey
    I did it just for you Bob.
    I'm sure what's his name is crying in his beer somewhere.
  16. DonL

    DonL Out of the Trades

    Messages:
    3,909
    Location:
    Houston, TX

    Great that you have it working.


    A Insult was not intended, But if the shoe fits then wear it.

    You may have been worried about nothing. The Caps can blow later if they need replaced. Just make sure your amp is fused properly.

    I stand by my Rule, "If you don't know the difference between Series and Parallel electricity, Then You should not be playing with electricity".

    Check out ohms law. The thing that Speakers and AC Line wiring have in common is that they are both AC, Just different output frequencies. And the AC line has a lot more power that can hurt you, If played with incorrectly.


    Thanks for pointing out my English downfalls. I wish I was as good as You. Can you play the French Horn ?

    I am French, and I majored in Electronics, Not English.


    Enjoy.
  17. BobL43

    BobL43 DIY Senior Member

    Messages:
    1,786
    Location:
    Long Island, NY
    ah, ................................never mind; I did say I was out.
  18. DonL

    DonL Out of the Trades

    Messages:
    3,909
    Location:
    Houston, TX

    You did ?

    But You did not say "Over and Out".


    I must be in the wrong QSO.
  19. CanOfWorms

    CanOfWorms Member

    Messages:
    174
    Location:
    New Jersey
    Yeah I overreacted. That's kind of my deal.

    Everyone I talk to that is in the know says this is a very easy recap job. It would certainly be cheaper and easier than replacing the transformers.

    I can't play the french horn, but I can play the didgereedoo.
  20. John in herndon

    John in herndon New Member

    Messages:
    25
    Location:
    VA
    Using a Variac® to gradually raise the voltage in a tube amp

    I used to be in the audio repair business and used this technique all the time on both tube and solid state amps. It prevents doing a lot of damage if you didn't find all the blown components.

    That said, you have to use a VARIAC® or variable autoformer to do this because this preserves the sine wave of the AC power. Solid state dimmers do not do this. They use SCRs and TRIACs to vary the voltage by delaying the turn on point of each individual cycle of the AC waveform. The result is a non sinusoidal waveform which would not work to power an amplifier or other electronic device.

    If it doesn't weigh 10 pounds or more it is not a transformer and won't work.
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