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Tube transformer voltage doulbler

Discussion in 'Home Brew' started by T23, Aug 1, 2012.

  1. T23

    T23 Active Member

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    I have a sweep tube amplifier, currently it has 2 6JU6 tubes in it, with 800 volts DC on the plates, the 6JU6 tubes consume 3.2 amps of heater current.

    I was thinking of converting this to use 2 or 3 811 or 811a tubes, would it be reasonable to use a voltage doubler circuit to get 1600 volt from the 800 to get enogh voltage on the 811a plates, and is the heater current sufficient?

    T23


     

  2. wavrider

    wavrider W9WDX Amateur Radio Club Member

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    If i am not mistaken each 811a uses 4 amps each filament voltage.

    Plate current would not be enough for the triodes.
     
  3. T23

    T23 Active Member

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    Ok, would you have a recommendation as to what tubes I could use that would be more avalable then the current ones?

    Thanks,

    T23
     
  4. wavrider

    wavrider W9WDX Amateur Radio Club Member

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    Not really I do not know of subs for those tubes.

    The triodes, 811A's or 572B's are the way to go for medium power amps.

    A single 811A is roughly 150 watts out. 572B is 300 watts oputput give or take.

    Maybe be better just to find a nice Texas star solid state amplifier and power supply, tubes are becoming hard to find and expensive.

    Either a real amplifier I.E. Amateur type or solid state is the way to go.

    Some have used old D&A phantoms and converted them to the 811A, but cost per output is not really worth it unless you can do the work yourself and have the parts laying around.

    Better to invest in upgrading the antenna system than an amplifier.
     
  5. BJ radionut

    BJ radionut Supporting Member and 6m addict

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    Key thing to remember when using a transformer and voltage doubler circuit is you loose about 1/2(50%) of your current rating....
    So the transformer which is rated 800v at 400mA is only 1600v at 200mA after the doubler circuit...
    So unless you have a transformer rated at 800v at 1 amp(1000mA) you do not have enough current even for a small single 811A.... when using a doubler

    To answer your other thread....Have not seen an 809 tube in many years....
    might look into the 807...still buy those pretty easy...but output wise not much difference than the 6ju6's... about 50-60 watts per pair...
    All the Best
    BJ
     
    1 person likes this.
  6. T23

    T23 Active Member

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    I like the 807s too. But I was hoping I could keep the grounded grid setup, but with the 807 it has its cathode tied to a grid i beleive and cannot be used in grounded grid configuration.
    Do you have any suggestions about using the 807 instead maby in a sifferent configuration?


    Thanks

    T23
     
  7. Robb

    Robb Yup

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    I think that if he could find more info on that transformer, he would know what to look for as far as tubes go. But if this amp of his originally ran 4 or 5 sweep tubes; then the amperage available might be around 2A @800V or more. Even the sweep tube is going draw some mA's X 4 or 5. In which case, he might be able to run two 572B's or four 811's (v.cheap tube) with a voltage doubler circuit. But this will REALLY depend on his xformer's output capacity.

    It is up to you T23; I'd say that you need to do some more homework,
    You need to hunt down some xformer specifications first before you buy anything - IMO . . .

    Edit:
    Forget about it; it will support just two sweep tubes . . .
     
  8. T23

    T23 Active Member

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    The transformer is supposed to handle up to 3 6ju6 tubes, so that means it should have 4.8 amps filiment current avalable. Ill have to look into the ma on the hv line. Its a kris boomer amplifer same chassis as the power pump.


    T23
     
  9. Robb

    Robb Yup

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    Filament current/voltage is another matter.

    The amperage and voltage for the plate is what should be your real concern here.

    Do you know if that transformer can run @220VAC?

    Seriously doubt it.
     
  10. T23

    T23 Active Member

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    I don't think it can run on 220, a 6ju6 tube consumes 45 MA on plate, so three should consume 135 MA on plate


    T23
     
  11. T23

    T23 Active Member

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    How about the Russian GU-50 tube, I can put a voltage doubler on the filiment on my transformer (the gu-50 requres 12.6 volts), and the plate current seems to be 50ma. Does anyone know if the socket diameter is the same as the current sockets?

    Heres the tube data.
     

    Attached Files:

  12. Robb

    Robb Yup

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    The 220v on the primary windings can help the tube have better peak current. Which should allow for greater overall output. If it doesn't; then you are limited to the amps total potential output overall. After all; this amp was designed to run just those tubes. Bet they didn't want to have to spend any more than they had to to sell it as described. Transformers aren't exactly cheap. You got what you paid for.

    There would be only so much head room available to keep it from being over-taxed and cause the xformer to burn out. Doubt that they made it capable to handle any more than it was specified to do.

    Let's say that your xformer has enough current from the HV windings to support a voltage doubler and two 811 tubes.

    If your xformer has the wrong heater voltage to make 811 tubes work; then you may consider adding another xformer to run those tubes.

    Just so we a clear on this. These xformers should have separate output windings for the HV, separate output windings for the heater, separate output windings for the bias, and separate output windings for the relay circuit. Or, it may have a second transformer to do what the first xformer doesn't supply by construction.

    I mean; do you have ALL of the specifications on that xformer you have? Do you have a link that can provide that info? If not; this all sounds like so much 'shooting in the dark' to me . . .
     
    #12 Robb, Aug 3, 2012
    Last edited: Aug 4, 2012
  13. T23

    T23 Active Member

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    I guess I'll just have to look at the transformer directly, I can't find any referance to what transformers kris amps used, so i'll have to see if there is some sort of number on the brick itself. I was thinking, ( I got the schematic here somewhere) that the two tubes migh have there filiments in a series and may actually be connected to a 12v winding....

    Strange... I just looked up the schematic and it does not have the heater lines in the schematic. I guess so they could use a various tubes and such as that goes....

    T23
     
  14. Robb

    Robb Yup

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    Some schematics will show the voltages; some not.

    I wouldn't go poking around a transformer with my hands and a volt meter to find out either like one would with a CB or a solid-state amp. See that your voltmeter can be used for HV, and then attach leads to it BEFORE it is turned on and AFTER it has sat long enough unplugged for the voltages in the caps to have diminished. Even then, making and using a 'chicken stick' to ground out what current is left is ESSENTIAL if you want to stay alive. These HV's can kill very quickly!

    You may well know what you are doing; but I say this for anyone else reading this who doesn't know about these dangerous high voltages present. IOW; be very wary. It is best to leave it alone if you don't know what you are doing.
     
  15. BJ radionut

    BJ radionut Supporting Member and 6m addict

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    T23: Looking over the schematic I found, on CBT...
    I noted these items....
    Filaments are in parallel...so the winding is 6 volts
    The transformer secondary B+ (AC)voltage looks to be 500-600v....
    The 800vdc your seeing is after the full wave bridge and filter caps...which will "amplify" the the AC voltage by 1.414 aprox....

    Primary Fuse is max 5 amps...(600 watts total)
    Loose a minimum of 100w of total capacity to the filaments/Lamps and relay circuit then:
    Judging from this info: I would say the B+ windings total current to be less than 1 amp MAX....most likely more like 500 to 700ma....
    I think you might just leave the amp as-is...
    I don't see any other tube other than a single 811a(which will not fit the case)(to tall)...that would be worth messing with...

    Even this would take a complete rework...tube socket/tank circuit caps & coil/power supply upgrades...shall I go on?....
    Not worth the effort!...IMO
    GL
    All the Best
    BJ
     
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