an RF amplifier with transistor and 807 tube for CW

Discussion in 'Amateur Radio Amplifiers' started by ASHOKDAS81, Apr 17, 2021.

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    ASHOKDAS81 QRZ Member

    Hi all,

    I have a 807 vacuum tube and I want to make a CW RF amplifier with it. I am thinking of using transistors in pre amplifier and 807 as final power amp. I have only one tube so I cannot make push pull amp. First of all I need to know if it will be possible to make such RF amplifier. If possible how difficult it going to be. I need the ideas to start planning a design. I do not have any experience in Vacuum tube designs, I have fundamental knowledge of electronics. Kindly help.
  2. KL7AJ

    KL7AJ Ham Member QRZ Page

    Yes...the 807 will put out full power with about a watt of drive in common cathode configuration
    W4NNF likes this.

    ASHOKDAS81 QRZ Member

    Ok, so I can construct a transistor amplifier to deliver approx 800 mW to the 807, but here the question is how the Transistor amp will be coupled to 807 and what type of bias to be given to 807. Also I have know the operating point of 807. I will supply 600v to the plate of 807.
  4. AD5HR

    AD5HR Ham Member QRZ Page

    Look up the data sheet for the 807 on Franks Electron tube page.
    Use the data listed under RCA (HB3).
    At 600V to the anode and .3 Watts of drive, expect 40W.
    out. (class C telegraphy).
    Notice that at 600V., the 807 is rated as CCS (continous commercial service).
    This means your 807 should last a long time.
  5. N1EBC

    N1EBC Ham Member QRZ Page

    Is the tube any good? Would be a shame to expend all this effort and it not work due to the tube.
  6. AC0OB

    AC0OB Platinum Subscriber Platinum Subscriber QRZ Page

    What's the frequency source, crystal or VFO?


    ASHOKDAS81 QRZ Member

    As a aspiring amateur radio operator, I like the challenge to bring up a vacuum tube. Its like bringing back a dino to life. I know I might fail not because of that it cannot be done but because of lack of components of that era. The frequency source will be crystal. I have a QRP cw trx that gives approx 800mW in output. I am planning to use that as a driver to the tube amp. The QRP rig is for 40m band, so my amp will work at 40m band. So far I have found following reference on the net. But it all tube design. I have to use transistor in driver stage.
  8. W9JEF

    W9JEF Platinum Subscriber Platinum Subscriber QRZ Page

    The QRP rig is likely 50 ohm output. But the 807 grid needs higher impedance (more drive voltage). I suggest a link-coupled tank circuit (Figure A) L1A connects to the driver output, L1B feeds the 807 grid:

    (Ignore figure B)​
    Jim . . . . . . . EARTH: LOVE IT OR LEAVE IT

    K4YNZ likes this.
  9. AC0OB

    AC0OB Platinum Subscriber Platinum Subscriber QRZ Page

    Here is a suggested start.

    Schematic 1 is the 807 stage in which the 807 is cathode biased and keyed by applying screen voltage via a relay contact to avoid any "Hot" key contacts. I use a relay with either a 6V or 12V coil I derive from the filament supply.

    Schematic 2 is the SS amplifier which is a modified version that has been around for quite some time. A low level digital signal is sent to a video amp and the video amp drives a Cable amplifier/CB final transistor. C7-L2 is a series resonant LC circuit to get you a nice 40 meter since wave.

    Schematic 3 is a crystal oscillator circuit in case you want to drive it from scratch.

    Schematic 4 is simply the LV power supply for the SS circuits.

    Generous Heat sinking of Q1 and the LM317's are a requirement.


    Attached Files:

  10. AC0OB

    AC0OB Platinum Subscriber Platinum Subscriber QRZ Page

    Here is a an 807 Cathode Keyed version with less voltage on the Key, due to RKB1.


    Attached Files:

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