4-1000A amp restoration

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

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  1. KU3X

    KU3X Ham Member QRZ Page

    I have two power supplies. One is 3900 volts key down and it takes less than 100 watts of drive to get legal limit out. The other power supply is 2900 volts key down and with 100 watts of drive I get 1250 out with my 4-1000 GG amp. If you demand 1500 watts out, then yes, you need a little more plate voltage. But the difference between 1250 and 1500, in DB's.......not one S meter on planet Earth will see the difference.

    Barry, KU3X
    www.ku3x.net
     
    Last edited: Jul 16, 2019
  2. KD2ACO

    KD2ACO Platinum Subscriber Platinum Subscriber Life Member QRZ Page

    Are you sure there's grid current with no drive? If there's no output with no drive (i.e. the amp isn't making its own music) there shouldn't be grid current either.

    An indication of current when there isn't any could mean that the meter circuit is sharing a return with something that's drawing current (giving you an erroneous reading).

    I'd check in with Lou W1QJ's suggestion for metering grid current (post #41). You can run a twisted pair of wire from the shunt to the meter and its multiplier resistor. This method is super simple to calibrate, with the amp unplugged none the less, and you know that the only thing the meter is getting is grid current.
     
    Last edited: Jul 16, 2019
  3. KM1H

    KM1H Ham Member QRZ Page

    Which could be gas if there is some internal blue glow. Too much and it goes BANG if the HV is in the 1500V or higher range. With many, if not most, 4X1's on Fleabay, hamfests, etc being recycled many times by unhappy users not wanting to lose money it becomes a real crap sh0ot. If the anode outgassing isnt too bad they can generally be regettered and give many hours of use.

    In broadcast use the anodes ran with enough color to keep gettered but long term storage negates that. A jig with ~1000-1200V and an adjustable bias supply plus air on the filament pins and glass is enough to obtain sufficient color while not being able to support an internal arc. Ive regettered a few dozen in the past when I was actively building 4X1 amps.

    Carl
     
    K2XT likes this.
  4. KD2ACO

    KD2ACO Platinum Subscriber Platinum Subscriber Life Member QRZ Page

    Yes indeed. It's been a while so I looked at the RF deck scheme again and if the amp in question is wired like that, the grid meter isn't sharing current with anything. It could be showing gas... ouch! :confused:

    Can you safely see the tube while it's on and keyed with no drive? Any blue glow inside?
    Time to be careful with how high the HT is until things are proven safe. A proper glitch resistor and fuses (and possibly a variac on the HT supply) are nice ideas here.
     
  5. KX4DV

    KX4DV Ham Member QRZ Page

    Yes, the amp is exposed for now in the rack. (I'll be enclosing it when it complete) I also added a window to watch the tube out front with a wire mesh screen. Tube seems to be in nice shape. No blue glow from plasma/gas. Yes, I'm cautious when it comes to the HT side of things. I make sure I'm "protected" by the rack or stand well away from it when I power up the HT side of things. I've got a glitch resistor inline as well. I'm using 240v for the pole pig, 120v to one leg straight, then the other leg through a variac on the rack to control 121-240v. When just using 120v, it outputs about 3600vdc.

    I've been busy with a dozen other things lately. But I did manage to replace the dials with vernier dials, night and day difference on tuning the amp now. I seem to recall about 800w output with 80w input just with being able to make fine adjustments. Still running it on low power right now, but next time I get to play with it, I'll step up the voltage to 5kv and see what it makes. Also all the testing has been on 10m, so that's the least efficient frequencies for that tube. I'll try to play with it on 80m next time, I bet it'll sing down there.
     
    W2VW likes this.
  6. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    My 4-1000A amp runs 1500W output on six meters (50 MHz), so ten meters is not a stretch for that tube at all.

    Many, many "low power" FM broadcast stations used 4-1000As in the 88-108 MHz region. Usually about 1 kW output, some maybe 500W. "College stations" and stuff.

    But mine isn't GG, it's grid-driven, AB1.
     

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