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pressure relief for paint can load?

Discussion in 'Amateur Radio Amplifiers' started by W1BR, Feb 2, 2018.

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  1. W1BR

    W1BR Ham Member QRZ Page

  2. K6BRN

    K6BRN XML Subscriber QRZ Page

  3. WA7PRC

    WA7PRC Ham Member QRZ Page

    Better yet, a few 400W flange-mounted RF power resistors + heatsink + fan. And, you don't have to worry about spilling air. Henry Radio (and many others) sell them, such as these: http://www.ebay.com/itm/371706401299
    "2 ea 800 Watt Hybrid 100 ohm Load Resistor to 500 MHz", $124.95
    There are many more lower-power devices (for less money).
     
  4. W1BR

    W1BR Ham Member QRZ Page


    No argument there... but I own the orphaned Waters load resistor and have a clean can. This a project. I have the TenTec 24okw which is good for 1500 watts. The Waters 334 handles over a kW as well. I really want a 2kW power attenuator for the spectrum analyzers... the largest I own is 300 watts/ 30 dB.
     
  5. K6BRN

    K6BRN XML Subscriber QRZ Page

    Bryan (WA7PRC):

    For those of us who are not destitute, the Bird attenuators and loads can usually be found on-line, either ebay or surplus houses, for very reasonable prices. Or at your local ham fest. The RF resistors are fine, too and are used in a number of commercial loads. If you'd like to make a project out of it, great! But better get most of the material surplus, because by the time you buy the resistors, heat sink, connectors and RF tight can (yes, you need to worry about this if you'd like broadband low SWR), fan, etc., you will surpass a good, used Bird 1 KW load on price.

    Brian - K6BRN
     
  6. W1BR

    W1BR Ham Member QRZ Page

    EBay resellers are getting top dollar for any Bird thermaline with a CCS rating greater than 500 watts. I'd buy a used high power Palstar dl2.5hp first. Not a matter of being destitute, rather a matter of paying what I am comfortable with.
     
  7. WA7PRC

    WA7PRC Ham Member QRZ Page

    I did. And, since all parts were scrapped by my employer, cost was ZERO:
    http://www.tinyurl.com/wa7prc-dummy

    As tested, it can handle 1500W (100% D/C) all day. VSWR is under 1.5:1 thru 50 MHz. That handles everything I can throw at it.

    For those not fortunate to have free parts, I showed that suitable parts for a big DL can be found for modest cost.
    Even those are almost twice the cost of a few parts.
     
  8. K6BRN

    K6BRN XML Subscriber QRZ Page

    Peter (K1ZJH):

    I use a calibrated Bird 8325, 500W (continuous) oil cooled 30db attenuator in front of my amps under test, followed by a calibrated 30 db low power attenuator, before going into my spectrum analyzer or power meters. It handles 1 KW just fine for a limited time (30 seconds is my rule of thumb). You can sometimes find these for about $250-$350 on-line, and are a very good value. Going up beyond that gets a lot more pricey and heavy, in precision attenuators. Your ideal 30db attenuator might be the Bird 8329, but expect to pay $800 - $1400 for a decent used one, on a good day.

    That said, power accuracy across a broad band is just not critical with a spectrum analyzer used on HF frequencies. Minimal tilt across about 200 KHz is all you need for very good results at (for example) 14 MHz. Measurements are invariably relative to the test tone(s) driving the amp, so absolute amplitude accuracy is not needed. And a decent sampling RF coupler can do that just fine (is not expensive and is easy to make). A 1KW capable, 2 KW intermittent 50 ohm termination, like the Bird 8251 can often be purchased on line for $250-$350 plus shipping - but then you already have this covered so all that you need is the coupler. I use this method quite a bit, also.

    Brian - K6BRN
     
  9. K6BRN

    K6BRN XML Subscriber QRZ Page

    Peter (K1ZJH):

    Keep looking. I just bought another 500W Bird 30 db attenuator and a 1 KW 8251 load, both in excellent shape, for $250 each. One on ebay, one at the TRW Swap Meet. So reasonably priced units are there, you simply have to keep your eyes open and be patient.

    Bryan (WA7PRC):

    Excellent! You have a very good source of RF parts - way better than mine - and free. BTW... a VSWR of 1.5:1 up to 50 MHz is not stellar when performing precise testing. You might be able to do better if you improved the RF containment the resistor is in. I recently disassembled, inspected and swept a 250W commercial unit that uses a single tab resistor and it was within 1.2:1 SWR up to 600 MHz with no lumps in its response - I was very surprised. In the case were two broad, copper tuning tabs that looked like they were hand adjusted to tweak the response (yet the response was very flat). I'd send you a photo, but am travelling just now. My buddy picked it up for just $20 at the same swap meet I purchased the 1 KW Bird at.

    Brian - K6BRN
     
  10. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    DWP in L.A. is...that's where I get mine.

    Local substation on Nordhoff Ave, bring a jug and ask nicely.:)
     
    WA7PRC likes this.

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