valve amp power supply

Discussion in 'General Electronics Chat' started by Roque, Jul 18, 2015.

  1. Roque

    Thread Starter Member

    Sep 16, 2014
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    hi tech gurus , I am working on a project of making a valve amp for guitar.In order to get the desired volts of around 350v for the valves i have used two different transformers the primary of the first transformer is connected to 240vac and the secondary winding of 12vac is connected to the secondary winding of the other transformer and so i get a output of around 350v dc after rectifying and filtering.The amp works great but the first transformer literally gets to boiling point ...very hot , which is no good.any help would be greatly appreciated ..Ta
     
  2. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    Get the right (single) transformer...

    The 12V winding on the first transformer is overloaded.
     
  3. Roque

    Thread Starter Member

    Sep 16, 2014
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    hi Mike are transformers available which can output 300v ac , also would need a tap that i could get 6.3v too.thanks for your reply.
     
  4. Roque

    Thread Starter Member

    Sep 16, 2014
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    would identical transformers do the trick?..
     
  5. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    Back when I was playing with tubes in 1958, such transformers were as common as dirt. Nowadays, not so much...

    It might be easier to find two transformers: one that makes 300V from line voltage; another that makes 6.3V from line voltage.

    Try this link: Pricing seems to reflect the gullibility of the believers in the vacuum tube religion.
     
    Last edited: Jul 18, 2015
  6. Roque

    Thread Starter Member

    Sep 16, 2014
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    thanks Mike will give it a read...yeah it is hard to find transformers that would do that..but will definitely have a read in the site you suggested and will give it a shot..thank you once again...cheers.
     
  7. Reloadron

    Active Member

    Jan 15, 2015
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    Don't know your location but here in the US Hammond still manufactures vacuum tube plate transformers with or without filament voltage. Also the distributor Allied Electronics had their own line out which I believe was possibly made by Hammond or maybe Stancore. What is your current requirement?

    Anyway, you may be able to get things done using a single plate transformer.

    "Classic" - Tube Transformers


    Ron
     
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  8. Roque

    Thread Starter Member

    Sep 16, 2014
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    Hi Ron..thank you for your reply..I live in Australia and have looked up various stores couldnt find a transfomer that would give me around 300v dc. will check the links you sent and hopefully might find a solution..thanks Mate.
     
  9. #12

    Expert

    Nov 30, 2010
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    Try measuring a 40 watt fluorescent ballast. I phoned the MFG and they said it produces about 400 volts. Subtract the loss in the rectifier tube or find out he meant, "RMS" and the rectified voltage is going to be way too high. Anyway, worth a measure if it doesn't cost you a penny.
     
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  10. Roque

    Thread Starter Member

    Sep 16, 2014
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    thanks buddy.
     
  11. Roque

    Thread Starter Member

    Sep 16, 2014
    68
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    hello i have managed to use the same winding to get the 12dc for the heaters. like in the image ..the 1st transformer now stays warm can touch and not too hot that i could previously smell the transformer...is it safe if it stays warm can i put a fan in to keep it cool???? is it normal ?

    1437290021288ns.jpg
     
  12. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    I dont understand the tube filament connection?
    Most tubes are designed to operate on either 6.3Vac or 12.6Vac using an indirectly-heated cathode, meaning that they do not have to be operated on DC, so what are the diodes you depict in the schematic?
     
  13. Roque

    Thread Starter Member

    Sep 16, 2014
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    just rectifiers havent drawn the entire bit..i read that heaters could use 12v dc as well ...whats happening now is i have left it on for a while now say for around 2 hrs or little more its warm can touch it but cant..stick my fingers on it for long ...confused as to whether it will eventually burn the transformer away..:-(
    can i put in a fan to cool it.? am i heading in the right direction or am i missing something?
     
    Last edited: Jul 19, 2015
  14. Roque

    Thread Starter Member

    Sep 16, 2014
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    also Mike the amp sounds sweet...using a 12ax7 in preamp and a el84 in power stage..also noticed the el84 glows not so bright.
     
  15. Roque

    Thread Starter Member

    Sep 16, 2014
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    Hi Mike sorry i meant i cant stick my fingers on the transformer ..can touch though.
     
  16. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    Post the full schematic. I think I see why your filaments are dim...
     
  17. Roque

    Thread Starter Member

    Sep 16, 2014
    68
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    sorry Mike i am trying my best to get my hands on the schematic ..looked in all my circuit folders even searched the net..i built this amp a while ago ..initially started with a pre amp project ..then after a year or so decided to add a power tube cause i started to love the sound of tubes .. will do another search hopefully i might find it and can post it here.
     
  18. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    I am still confused about the two trannys you are using now...

    Are they identical?

    Do you have any data on them? part numbers, data sheets?

    Do you have access to an IR non-contact thermometer (looks like this)? If so, measure the temperature of the tranny after it has been on for a couple of hours. 40degC or less is likely ok.
     
  19. Roque

    Thread Starter Member

    Sep 16, 2014
    68
    2
    the trannys arent identical ..they different.they are something i dug out from my box of goodies that my wife always wants me to get rid of ....hehehe..will send you photos. will try and check the temp too dont have an ir thermo but will find a way and let you know ..have just turned the amp off ..
     
  20. Roque

    Thread Starter Member

    Sep 16, 2014
    68
    2

    hi Mike here are a few photos its not a piece of art hehe its my first go at a tube amp so bear with the photos..i measured the temp with a standard thermometer and it clipped after 42 ..cause thats too high for body temp.say it would be in 50 or the 60 range guessing.
     
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