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4-1000A amp restoration

Discussion in 'Amateur Radio Amplifiers' started by KX4DV, Jun 8, 2019.

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  1. W1QJ

    W1QJ Ham Member QRZ Page

    If it were my amp I would upgrade it a bit with directly grounded grids. Then float the B- and use a diode to ground from the B- to clamp the B-. Tom W8JI has this at his webpage. Then once you do this you can monitor the grid current between B- and ground. You can add the "vox relay" which can be used to bias the tube off and on therough the self bias resistor. The cut off is 99% complete and perhaps only a couple of millamperes gets through. It barely shows on a 0-1 amp meter.
    KU3X likes this.
  2. KX4DV

    KX4DV Ham Member QRZ Page

    Well, all the work was for naught. The dang TR relay has seen better days on latching. All over the place on SWR when keyed. I've got another relay like that frame on the way. I was thinking about using a modern one, but that'd mean I'd have to have redesigned all the routing of the wiring internally. This one also is a 3 pole relay vs. the two. So I'll pull out the VOX relay I added and just tack that into that open pole.
    KU3X likes this.
  3. KU3X

    KU3X Ham Member QRZ Page

    If you get at the contacts on the new relay, give the Hy power antenna a tad of an bend in it so that contact is made before the relay fully closes on transmit. This helps prevent hot switching and pitting that contact. It give the Hy power contact a tad of a lead time.

    KX4DV likes this.
  4. KX4DV

    KX4DV Ham Member QRZ Page

    Yeah, I figured I could try to tweak the one I have back into shape at least on latching. Bypass it's solid all the way through. But I figured the $15 to replace it would pay dividends on when I'm ready to pull my hair out when it frags under a load on the output side. I'll keep the solenoid part around though for a spare.
  5. W7RY

    W7RY Ham Member QRZ Page

    The grid is RF grounded with the .01 and almost DC grounded with the resistor. There are better ways to get grid current with the center tap of the filament transformer (cathode).
    I too have that schematic given to be by my now SK Elmer, Bud, WA7JZR, (W7BUD). It may be from one of the older Editor and Engineers (Bill Orr) handbooks. I had the exact amplifier when I was 16 years old and a young General class ticket holder.

    In this circuit you ground the center tap of the filament transformer (provide a DC path to ground for the cathode) to draw idling current and for transmitting.

    Good luck on your project.
  6. N8CBX

    N8CBX Ham Member QRZ Page

    Seriously, forget this GG, cathode driven crap and configure the amp as a grid driven tetrode like it was designed to be. I'll show you how to do it....I just finished building a 4-1000A, grid driven tetrode amp...and loving it. You will too.
    Jan N8CBX
  7. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    My HB 4-1000A amp is grid-driven also...but reducing the drive from a 100W PEP exciter is really important.

    With mine, 10W will drive it to "full power" easily so a built-in power attenuator (at the input) is almost a must unless using dedicated QRP rigs to drive it.
  8. N8CBX

    N8CBX Ham Member QRZ Page

    Use a solid state 100W PA rig that has a power control knob and ALC.
    Jan N8CBX
  9. W7RY

    W7RY Ham Member QRZ Page

    It's easy and works well.

    Not sure it's crap if you don't grid drive a 4-1000 is it now?

    Jim W7RY
  10. KM1H

    KM1H Ham Member QRZ Page

    But obsolete and prone to air ingress. Finding a good one these days can be an exercise in frustration and at best will need a serious regettering.

    I built several one and two tube versions, GG and swamped grid driven back when good pulls were free from commercial AM and some old tech FM stations. Those are long gone.

    With a typical 100W exciter a tuned grid input is for the birds and nobody runs a tetrode that way any more.....ACOM, Alpha, Emtron, QRO, etc, etc.

    The 4X1 loves HV and I ran them at ~4500-6000V based upon customer requirement and what iron was readily available at low cost. Dahl was a last resort and only for those with deep pockets.

    If you want a real tube get a 3CX3000A7 or F7 and use the grid as a dummy the Eimac/Chinese version can be rebuilt.
    Last edited: Jun 27, 2019
    K2XT likes this.

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