All 4-1000 gurus step inside

Discussion in 'Amateur Radio Amplifiers' started by W4EKY, Jan 16, 2017.

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  1. W4EKY

    W4EKY Ham Member QRZ Page

    I have three filament transformers, 2 have 115v primaries. The 3rd has a 240v primary. I wanna use the panel mount variac on the filament transformers so i can keep the filament voltage touched up on 7.5v in case the line voltage goes up. So one transformer on each leg of the output of the variac?
  2. W4EKY

    W4EKY Ham Member QRZ Page

    How complicated is the screen supply to build?
  3. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Not complicated at all. I previously posted a link to my complete schematics and parts lists for a 4-1000A grid-driven amp. The power supply is three supplies on one chassis: Plate HV, screen and control grid bias. I put the filament transformer on the RF deck chassis close to the tube because the current demand is high, and this helps keep the interconnecting power cable more flexible (without having to use any large conductors).

    I don't think you need to adjust filament voltage to accommodate line fluctuations. I've never done that and have used my 4-1000A amp "portable" many times, powered by a 5kW gasoline generator whose output was not well regulated at all and the amp did fine, no tuning fluctuations, no power fluctuations, no shortened tube life (the tube in my amp was "used" and a pull from a BC station in 1984, has thousands of hours on it since then, and is still perfect; that's 32 years). I don't use a variac on anything, as that just adds a lot of weight, a bit of heat and loss, and doesn't bring anything to the party.
    WA7PRC likes this.
  4. KF7TLL

    KF7TLL Ham Member QRZ Page


    I agree with Steve,
    A grid driven 4X1 is more efficient and requires less drive and less plate voltage to work properly... you was looking at doing a 2 x 4X1 in GG amp that will require a LOT of plate voltage and have to drive the SNOT out of it, a regular 100W rig will not be enough. Probably have to use a 4cx250 to drive that beast.

    I myself am doing a GG 4X1 amp 3KV on plate and will drive it with about 150W. I am NOT a electrical engineer or even remotely close that is why I am doing it GG just for simplicity.

    Good luck in your Build what ever way you go. If you got the smarts go Grid driven

    73's Bruce KF7TLL
  5. N8CBX

    N8CBX Ham Member QRZ Page

    Just buy Ian White's tetrode control board. He has designed a brilliant system with EVERYTHING needed (variable screen PS/regulator, variable grid PS/regulator, T/R switching & bias control, G1/G2 current monitoring and so on).
    Also, his manual is a necessary document to read about tetrodes.
    I also suggest not to jump into building a large tetrode amp right away. I suggest building a 50W amp FIRST using a 6146B first (built on a breadboard) to really learn about tetrodes.
    In regards to the filamant transformer, MFJ sells an excellent one that has the multiple primary taps needed to properly set the filament voltage. Then you can save your Variac for use on the workbench where it belongs.
    Also, another point is WHERE TO SET the LOAD CONTROL with regard to screen current. This is the most important to learn using a tetrode, and I suspect most operators don't load the tube properly and the result is non-linearity and exceeding screen dissipation. Eimac data sheets will give examples of AB1 operation and will specify the screen circuit that one needs to know to set the tube loading.
    Another point is the input circuit to drive the grid with consideration of the tube's internal capacitance. Typically, we use a Pi net with C2 as the tube's internal capacitance and it's tuned with a variable L. But, there's more to it than that. This is why it's better to get your feet wet starting with the 6146 and if the tube goes it's not that expensive loss.
    Jan N8CBX
    Last edited: Jan 23, 2017
  6. KK4RSV

    KK4RSV Ham Member QRZ Page

  7. KK4RSV

    KK4RSV Ham Member QRZ Page

    Hi Mr WB2WIK I would love to have a caopy of your schematic if you don't mind sending me one.
  8. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    I already posted it.

    Click on the blue highlighted link in Post #16. Complete schematics and also photographs.
    N2EY and KK4RSV like this.
  9. W4EKY

    W4EKY Ham Member QRZ Page

    I have been reading and looking at different schematics for my 4-1000 project and it leads me to one question, can the z50 choke on the bypass caps be mounted in the rf deck around the tube, plate choke and tank circuit? Or does it have to be mounted away from any RF source.

    Also is the z50 a necessity or is it just being used as a saftey choke?
    Last edited: Feb 27, 2017
  10. W4EKY

    W4EKY Ham Member QRZ Page

    Here are a few pics of my project. Please tell me if you see anything that needs changed or moved. Open to all opinions..overlook all the blue masking tape on the vacuum cap and cabinet. Just trying to protect the fresh battle ship gray paint.

    Attached Files:

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