ad: AlphaRF-1

4-1000A amp restoration

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

ad: L-HROutlet
ad: l-rl
ad: Left-2
ad: L-MFJ
ad: K5AB-Elect-1
ad: MessiPaoloni-1
ad: Subscribe
  1. W1QJ

    W1QJ Ham Member QRZ Page

    I think you are better off grounding the grids hard to the chassis and lifting the B- above ground with a diode and meter the grid current between B- and ground.
     
    WA7PRC and KU3X like this.
  2. W2VW

    W2VW Ham Member QRZ Page

    It's nice to have a grid current indicator just for the control grid with this particular setup.

    I've run into plenty of pulls which were apparently used in hamateur service with the screen grids and control grids tied together. Especially 4-400s. 4-1000 is same but maybe even worse as people may have had a crummy power supply under 4kv.

    It's easy to overdissipate the control grid when trying to work North Korea.
     
  3. K2XT

    K2XT Premium Subscriber QRZ Page

    "Damn the torpedoes. Full speed ahead! Crank up the B plus. I have more 4-1000s" said Admiral Parascondola.
     
    W2VW likes this.
  4. KM1H

    KM1H Ham Member QRZ Page

    That may be true for those who never go above 40 or maybe 20M or never actually built a 4X1 amp and used it extensively thru 10M, including WARC, at current power levels (or more). In reality that tube can get real squirrely when it comes to layout and it gets worse as the HV goes up. Toss in those tubes with enough gas, the user having no clue about regettering and suddenly there is a lot of stained undies.

    At the old 2500V and 1000W INPUT limit they were docile no matter how haywire things were, especially well used pulls that needed 120-150W to drive.

    Carl
     
  5. KX4DV

    KX4DV Ham Member QRZ Page

    I have the grid metering squared away now. I used a 1ma FS meter and ended up bridging 3 1ohm resistors across it to get 300ma to read FS. I've been testing on 10m for now, since I know it's going to be the most problematic. My radio only puts out about 75w on 10m. But I saw 400w out of it. I'm going to redo the load and tank capacitors, they're just a direct 1:1 dial on them. Touchy as all get out. I'm going to swap over to a vernier dial onto them to allow fine tuning. Also I know I have room for more voltage. I'm currently only running ~4kv. I wanted to get everything input/output/metering 100% before turning up the wick any more.

    As noted, I saw about 20mA of idle grid current when keyed and no drive. Only saw 100ma peak grid current testing. Plate current showed about 500ma.
     
    Last edited: Jul 15, 2019
  6. KU3X

    KU3X Ham Member QRZ Page

    With 75 watts of drive at 4KV you should easily get over 1kW out. Put a lot of effort into the tuned inputs.
    Barry, KU3X
     
  7. KX4DV

    KX4DV Ham Member QRZ Page

    The load and tune are impossible to get perfect, it should be better when I swap over to the dials. Also it looks like my HV meter is wrong. I was showing 4500v, but it's about 3500v.
     
  8. N8CBX

    N8CBX Ham Member QRZ Page

    If it's really 3500vdc on the plate, thats too low, it needs to be above 4,000 as the minimum.
    Jan N8CBX
     
  9. N8FVJ

    N8FVJ Ham Member QRZ Page

    When are you going to get this amp operating? It's been 5 weeks.
     
  10. W2VW

    W2VW Ham Member QRZ Page

    Pressuring someone with project completion involving potentially deadly apparatus is not well advised.

    Ever watch someone die because they were in a hurry??

    I have.
     

Share This Page