AN/URC-32 RF amp revival

Discussion in 'Technical' started by K4TQF, Nov 18, 2015.

  1. K4TQF

    K4TQF Member

    Well... I figured this would be the easier of my projects to complete first so I can spew more electrons out into the ether.
    Talk about a "Bang stick ! Check out the way the PS door interlock works... shorts HV to ground. Does something look funny about this diagram? Or is it just me?
     

    Attached Files:

  2. W5HRO

    W5HRO Administrator

    It looks like the HV output shorts to ground the same time the AC voltage on the primary is released. They are just shorting the output when that happens to make sure the caps are discharged completely.
    .
     
  3. K4TQF

    K4TQF Member

    Why is the negative side of the 2KV bridge connected to the + rail on the 400V bridge?
     
  4. W5HRO

    W5HRO Administrator

    Probably for ground isolation to the RF amp.
    .
     
  5. K4TQF

    K4TQF Member

    Well I guess I should RTFM before I ask stupid questions... this block diagram on page 396 'splains it...

    PP-2153U 001.jpg
     
  6. K4TQF

    K4TQF Member

    Now, If I can just figger out all the interconnecting keying lines and interlocks,:icon_crazy: maybe I can fire this thing up !
     
  7. W5HRO

    W5HRO Administrator

    Be careful and check the phasing of those two supplies when they are combined together like that. The 400V they are feeding into the upper bridge is also forward biasing the diodes in that bridge.

    It is an interesting design concept though ;)

    I'm here working on my 4-400CG deck today and getting ready to remount the new regulator board. I won't have the relay for the AB2 bias switching until next week though.
    .
     
  8. W5RKL

    W5RKL Member

    I operated AN/URC-32 transceivers back in my Navy days when I was stationed aboard ships. At sea they were used primarily on HF side band HI-COMM frequencies. When in port they were tuned up on HARBOR COMMON 2.716Khz AM.

    73
    Mike W5RKL
    RMC(SW) USN RET
     
  9. K4TQF

    K4TQF Member

    OM:
    Did you do any maintenance? These things look to be a maintenance pain when taken as a whole. I am only in possession of the AM-2061 RF amp and the PP-2153/U HV power supply. There are some other voltages needed to key this thing... i.e. 28VDC.
    TNX, Mike,
     
  10. W5RKL

    W5RKL Member

    Hi Mike,

    I'm sorry but I'm not a URC-32 tech., never worked on one but I've watched Navy ETs work on the URC32s.

    I found the following link to a website that contains significant information, including links to manuals and field changes covering the URC-32, that you can download.

    http://www.virhistory.com/navy/xmtrs/urc32/index.htm

    I suspect the links to the various URC-32 manuals and field change data would be valuable information.

    Another website that may be of some help is W1LJN's website on the URC-32:

    http://www.qcwa.org/w1ljn_station3.htm

    73
    Mike W5RKL
     
  11. K4TQF

    K4TQF Member

    Mike:
    Thanks for the links. I have downloaded the complete maintenance manual and had it printed at LULU.com for $15. Cheaper than a printer cartridge ! I'm just glad I don't have the complete rig to deal with.:eek:
     
  12. K4TQF

    K4TQF Member

    Well I have determined that the power supply is OK. Figured out the interlocking(s) and key line and put it to the acid test. Connected it to a ME-165 dummy load and powered it up. Plate current looked normal. After a few seconds the smoke came wafting out. Didn't smell like resistors though. Put it back on the bench and upon closer inspection a couple of the Vitamin Q caps in the bias supply looked sick. Replaced all the electrolytics I could find. Fired it back up for a few seconds and the power supply was groaning. Excessive current flow somewhere. ( without drive ) Variac is pretty much useless as some of the interlocking relays are in the 2KV & 400VDC lines. I'll get there, it will just take a lot of trial & error.
     
  13. W5HRO

    W5HRO Administrator

    Smoke that sucker :biggrin: Just put the turkey or ham inside and go for it!

    Your interlock problem gave me an idea for my 4-1000A amp supply though ;)
    .
     
  14. K4TQF

    K4TQF Member

    I'm thinking I may have a bad pair of 4CX250B. I do have spares... but I want to do some further checking before I put them in.Never could identify the smoking part.
     
  15. WD5JKO

    WD5JKO Member

    You might run the tubes with filament on only for 12 hours or more. Then when finally putting the HV to them, add something like a 1K ohm 2 watt resistor in series with each plate lead. Don't key the drive, but just apply the HV to the plate, screens, and with cutoff bias on G1. A gassy tube will fry the resistor in short order. Letting the tube sit there filament only can take care of some tubes, others not.

    Jim
    Wd5JKO
     
  16. K4TQF

    K4TQF Member

    Jim:
    Good idea. I let the thing "warm up" with filaments only for about a week before I tried any HV. Each plate has a 47 ohm resistor in series but the 2 turn #16 coil around them is taking all the current. I think those are for parasitic suppression IIRC. Funny thing is... the plate meter did not show excessive current, either in total or when switched between tubes. Those bad electrolytics were all in the bias supply. I'm not satisfied that I have all the interlocking correct yet. There is a time delay relay connected the primary of the transformer providing the bias power that is supposed to kick on the plate relay 17-20 seconds after the plate is manually switched on. As it is now, the plate comes on immediately, when the "plate on" switch is operated, with no delay and, there is no bias showing up where it is supposed to. My try-it & fry-it method didn't work, so more head scratching is in order... back on the bench she goes.
    I might add that everything is properly fused and no fuses were harmed in the process.
    TNX, Durff
     
  17. WD5JKO

    WD5JKO Member

    Perhaps try keying up with the RF output tubes removed, and plate wires moved away from a short to ground. If you have access, then perhaps you can verify the proper bias and screen voltage.

    Jim
    Wd5JKO
     
  18. K4TQF

    K4TQF Member

    Jim:
    Yeah... I tried that yesterday. Problem is, this a Collins built piece of military gear. You know what that means... you have to do open heart surgery with the back & front plates removed to get to anything. Part of the bias, -45V does appear@ pin 15 on the connector and I was able to identify that it is not present.( it is picked off to key the antenna relay ) So, I've put back on the bench. I'll just start from the ground up and go thru it. So much for my short cuts...
    Thanks, Durff
    PS: could be badly tarnished silver contacts...anything...
     
  19. K4TQF

    K4TQF Member

    Well, this thing is a head scratcher... 2KV on the plates, 400V on the screens, & adjustable bias -120-165V. 115 AC Input is about 2.5A with filaments on and plate on. When I ground the key line (24VDC ) the input current goes to 12.5 amps. ( it is fused at 15A.) Funny thing is... the plate current is at or below the recommended 200MA for each tube. The 1K resistors fried on both tubes. No drive is applied. BTW, the outputs are 7580/4CX250R.
     
  20. W5HRO

    W5HRO Administrator

    :eek: :eek: :eek: .That may be your problem...

    Are the screens still at 400V when the tubes are in with no drive? Is there a screen clamp when no drive is present?
    .
     
  21. K4TQF

    K4TQF Member

    Screens on all tubes, drivers and outputs, are grounded by the keying relay when not keyed. When keyed +400 is applied. This is acting the same way as before when drive was applied. I'll give it another try.

    The idea was to connect my footswitch to a relay to key the KX3 & the amp at the same time.

    The head scratching part is... where the heck is all that input wattage going? 1200+ watts @ 115VAC input for 125 watts RF out? :surprised: Maybe so, the PS is fused at 15A. the PA is fused at 1 amp and niether of those fuses have blown. If this is "normal" with a big assed blower keeping the PA tubes cool, I'm going to have a very warm shack ! :icon_thumbup:
     
  22. K4TQF

    K4TQF Member

    Well... this is the only relay I could find.

    IMG_0165.JPG
     
  23. W5HRO

    W5HRO Administrator

    Maybe the blower is bad and drawing excess current. Have you tried connecting it by itself yet to see what happens? That wouldn't explain why the plate resistors burned up though. If there is no screen clamp when keyed and no drive is present then... It doesn't matter what it does when it's not keyed.
    .
     
  24. K4TQF

    K4TQF Member

    Good blower... I just stuck those 1K resistors in there as per Jim WD5JKOs suggestion. Probably got 2 bad tubes. Now that I look at them closer, they are the R version. 7580 / 4CX250R
    New development, neither the external key line, nor the manual KEY toggle switch on the front panel work. Bet'cha I blew that $6 internal HV fuse. No HV= an open interlocking circuit. Rats, back into the depths of the beast I go... now, where did I put that bang stick?
     
  25. K4TQF

    K4TQF Member

    Well, yes, the HV fuse was blown. I replaced it and the rig came righ back up. Driving it with 100mW from the kx3... still no output. Adjusted the bias to 100ma per tube and the ac input power has dropped to 5.2 amps. Don't know if the bias adjustment did that or ? Lots of hot air coming out the front vents.