PL-175 / 4-400 Amp

Discussion in 'Technical' started by K4TQF, Jun 13, 2016.

  1. K4TQF

    K4TQF Member

    :eek:Another 4-400 amp followed me home...

  2. WD5JKO

    WD5JKO Member

    Let's see some inside views of tube porn...Those 4-400's are some nice jugs!


  3. K4TQF

    K4TQF Member

    It came with a PL-175. I have a stash of 4-400's in Maine
  4. W5HRO

    W5HRO Administrator

    I think Jim's first pic was a pair of 4-1000A's and not 4-400A's :mrgreen:
  5. W5HRO

    W5HRO Administrator

    Is that amp all in tact? Supply and everything?

    If so that will save you from having to build up other one for now.

    I have my 4-400 RF deck finished in the big rig and just need to add the last couple of final touches to it then upload the photos.
  6. K4TQF

    K4TQF Member

    No HV supply, but I have several of those.
  7. W5HRO

    W5HRO Administrator

    Get one of the Penta PL-4-400CG tubes like I have in mine. It has significantly higher plate power dissipation compared to a standard 4-400A.
  8. K4TQF

    K4TQF Member

    It looks like it will be ready to go with a little cleaning, cap & connector replacement, etc... Not much at all. I'm taking 4 spare power supplies and most all of my parts stash back to Maine July, 2. The XYL thought she would cock block me by renting a 16' truck! HA... All they had available was a 26 footer.... Load ' ER up boys !!!
  9. W6MQI

    W6MQI Member

    ROFL :lol:
  10. K4TQF

    K4TQF Member

    Before I left Maine in April, Larry NE1S said, "bring all that old junk up here". 36 tubs & counting, + 5 tube caddies, so far !

  11. K4TQF

    K4TQF Member

    Here's the PS I plan to use for the "new" 4-400 rig. The rack I've had since 1963.
  12. W5HRO

    W5HRO Administrator

    One more week from today...

    By the way Al was looking for you. You might want to send him a conversation message. .
  13. K4TQF

    K4TQF Member

    'Round to it'
    Somehow, I gotta squeeze 2KV outta that POS supply on the left. I think I'll strip it and run it thru the dishwasher.


    my new desk didn't even make into position until it was pressed into service as a workbench... OH,Well ::)
  14. K4TQF

    K4TQF Member

    After the failure of the SS amp, I decided to start rebuilding the HV supply for the PL-175 /4-400 amp. The XYL went over to visit the daughter last night, ( she's the one on the right... Bitch 1, in the middle, is the 15 YO who ran over my OWL with the lawnmower, Bitch 2 on the left (13YO). Bitch 2 was adopted from Ethiopa when she was 3 and is actually normal. Bitch 1 is homegrown and crazy as a shit house rat...I pity her poor husband or any person she comes in contact with !) )

    The Stamey girls in Boulder..jpg
    so, I ran the chassis thru the dishwasher ! UTC iron and all... still a nasty chassis.
  15. K4TQF

    K4TQF Member

    Well... I was gonna use some 5R4 "potato mashers" I have. But, they are on the cusp, rated at 2KV but only 250ma. The PL-175 minimum is 2KV@350ma. similar to a 4-400. The UTC iron is 1600VAC @ 325ma. So, I would be living on the edge. I have some solid state 866 replacments.... they may work.
  16. W5HRO

    W5HRO Administrator

    Yeah, use those. Mercury vapor rectifier tubes suck. The SS replacements are called licorice sticks.
  17. K4TQF

    K4TQF Member

    After running your chassis and transformers thru the dishwasher :eek:, check for obvious shorts or leakage between primary and secondary.:icon_thumbup:


    Connect your variac and bring up the voltage slowly...
    DO NOT connect the 110VAC in this manner:icon_thumbdown:

    Then, grab every meter nearby, and ramp up the primary voltage with a variac. Remember to connect meters in the most dangerous way possible.

    Also, have spare fuses on hand to replace the blown ones when you forget to turn off the variac in-between tests of the primary taps. This particular Xfmr a UTC a D-4050 has about 5 or 6 primary taps. So, at least have a box of 5 fuses nearby.

    The reading of 1/2 the secondary of 828VAC @ 125VAC input
  18. K4TQF

    K4TQF Member

    Grid input:
    Grid input. .JPG Grid input.JPG
  19. W5HRO

    W5HRO Administrator

    The only reason you got way with that is because those transformers are sealed, or at least you still hope so.

    I'm assuming from your post is that they still work after being soaked in hot water?
  20. K4TQF

    K4TQF Member

    Yeah... I figgered I'd go ahead and give 'em the "acid test". Power supply all good, so far.

    RF output chassis: blower bearings need re-packing & crappy SO-239s will be replaced. ( for RF & HV )


    But it sure looks purty when lit up

  21. K4TQF

    K4TQF Member

    Now I find myself doing some head scratching as I put this HV supply back together. It looks like I'll need to series a bunch of 330uf @450 volt caps. IIRC, 10 would give me something around 30-40uf @4500V. I'll prolly bridge each one with a couple of 2Watt 220K resistors. like this;

    These would be on either side of the UTC D-4049 choke I have on hand.

  22. W5HRO

    W5HRO Administrator

    Just out of curiosity, is that 4-400 amp an old class C RF deck or is it a class AB2 linear? I’m asking because 2000V is bit low anyway and you really need around 2500V for class AB2 linear mode. 2000V is just barely enough for class C though.

    What I'm getting at is that supply may not cut it. For class AB2 you need 2500V @ 350mA. That's with around 5W of drive power. You could increase the drive a bit and then run it in class BC mode for AM, but you still need around 2500V. 2000V is that tube's threshold point and it’s better to have it just a bit higher. 2100V to 2200V minimum would be much better. At 2000V and below the power will drop like a brick and yield high current in linear mode. Even in class C grid driven mode 2000V is really borderline. I run the one in my HB transmitter right at 2150V in class C to keep it over the hump.

    If it's class C grid driven and you cannot get the voltage up and it's below 2000V then forget it and find another supply/transformer.
  23. K4TQF

    K4TQF Member

    Don't know the lineage of the amp. It came with a Penta PL-175. I'll just fire it up and see what happens. Yeah, I'm living on the bleeding edge at 2KV even if there wasn't any sag. Tim took pity on me and swears he's bringing me some bigger iron when he comes to pick some Altec 200 watt amps from me next week. I had a W.E. Kenyon 3750V @1A transformer, but I left it back in Arkansas... I was just too damn tired to pick it up ! I could always use the 3KV supply in the plasma rig. Or, I could use the supply from the Collins URC-32... 2KV@ 500ma. It's a good solid supply. Don't know how this will all settle out yet.

    On 2nd thought, the Collins supply is together, working and has an external keyline connected to my foot switch. I need to move it out of the rack it's in anyway... I should just try it and see what happens.

    Looking at the PL-175 Class C data attached, this tube will do OK with 2KV.

    Attached Files:

  24. W5HRO

    W5HRO Administrator

    Try to run it up just over 2kV. From the looks of your grid circuit pic it would appear to be class C grid driven, but that's why I was asking, I wasn't sure. Does the RF input go to that tuned grid circuit?
  25. K4TQF

    K4TQF Member


    Looking at the data sheet on the PL-175, 2KV looks like the "sweet spot " to me.