4-1000A amp restoration

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

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  1. KX4DV

    KX4DV Ham Member QRZ Page

    Just an update. Got B- shunted and that is working correctly. Also replaced the TR relay and it's working beautifully now. Only had my 817 handy (Watch out now, I don't want to drive this thing too hard!) but it's working! I dialed it into 28.425 since the higher frequencies are where the 4-1000's start showing issues. With 4500v on the plate and all 2.5W of drive, I saw 20w out of it on the bird meter. When times allows, I'll get onto it with something that can actually drive it. (Either the FT-450d or the FT-991 because they're handy) I traced out the grid metering circuit. The diagram shows that it should have been shunted to about 1.2ohm to ground. So I found a 3w 1.5ohm resistor for that task. Didn't see any grid current yet, but I didn't expect it with what little drive.
     
  2. N8CBX

    N8CBX Ham Member QRZ Page

    You know what happens to the tank Q at that high plate voltage?
    Jan N8CBX
     
  3. KM1H

    KM1H Ham Member QRZ Page

    Nothing when designed for it; the tube is rated to 6000V and runs ~5000V in commercial SW AM and FM BC use.

    Carl
     
  4. KX4DV

    KX4DV Ham Member QRZ Page

    Tried to tinker a little today on it, but didn't have much time. I did swap over to the 991 to be able to throw a little more fire at it. But my grid metering isn't working, so I'm going to have to track down that issue before I go any further. I did bump up to about 25w input and saw 200w out on 10m. I yanked the meter out of circuit and ran it through my multimeter just to test and saw about 25-30ma of grid current. But progress is progress I guess.
     
  5. KM1H

    KM1H Ham Member QRZ Page

    Thats what makes this all fun!

    My first KW amp was made from a pair of sorry looking BC-610's and other parts from Army MARS when I was in HS and had it done at 17. I was banned by my parents from using it on 10 and 15 but it had OK TVI suppression for the lower bands. Wound up with a pair of 250TH's modulated by 810's. RF and audio driven by a Viking I and this was at the peak of Cycle 19.

    That started a lifetime of working with amps for hamming, commercial, BC, and military.....almost 60 years.

    Carl
     
  6. N8CBX

    N8CBX Ham Member QRZ Page

    True...Most amateur projects ignore that point
    Jan N8CBX
     
    KM1H likes this.
  7. KX4DV

    KX4DV Ham Member QRZ Page

    I figured out what the problem is with grid current monitoring. I just duplicated the wiring from the SK. He mistakenly had grid current metering through pin 2, instead of 3. So I'll pull all the wiring out and reroute everything. I know pins 2 and 4 in the 1K tube share a common ground, so that explains why there was no meter movement. I'll get that squared away tomorrow. Then I think I'll be ready to start testing it more for output power and certainly more drive.
     
  8. KX4DV

    KX4DV Ham Member QRZ Page

    I swapped everything around, the grid meter is working now. It's a weston 301 300ma meter, 20ma FS. I used four 100ohm resistors to net a 25ohm resistor that I put in series. (24.8ohm in series showed full deflection with a 300ma load.) Only problem now is that it certainly isn't putting out the same power as it was before. I'm wondering if I need to revise the metering circuit. The documentation stated that they spec'd it with a 1ma FS meter in place. I'm wondering if I'm pulling ground too high for #3. Maybe I need to step back and rethink it. Resistor shunt perhaps? Swap over to a 1ma FS meter?
     
  9. KX4DV

    KX4DV Ham Member QRZ Page

    I went ahead and ordered a 0.1 ohm 3w resistor as a shunt. That will give the grid a nearly close to ground potential. Then I'll use a pot in series with the meter to fine tune it.
     
    Last edited by a moderator: Jul 7, 2019
    KD2ACO likes this.
  10. KX4DV

    KX4DV Ham Member QRZ Page

    I tinkered for about 5 mins with it today. Just jumpered the meter straight across. Went from 20w in/30w out to 20w in/200w out. So it's the meter causing the issue.
     
    KM1H likes this.

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