pressure relief for paint can load?

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

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  1. K6BRN

    K6BRN XML Subscriber QRZ Page

    Steven (WB2WIK):

    Straight mineral oil has a much higher vapor pressure than transformer oil, and so it tends to readily evaporate into vapor inside the cantenna, push itself out of the container through the easiest escape path and recondense on the top cover. Just like water, it does not have to boil to evaporate. Room temperature and some small daily temperature fluctuations drive this evaporation/recondensation process. I've had several brands of cantenna and they all develop oil on top of the lid, whether used or not, from this process. It is a slow but annoying phenomena. I'm sure you've had one and seen this.

    Brian - K6BRN
  2. K6BRN

    K6BRN XML Subscriber QRZ Page

    Brian (WA7PRC):

    Recently formulated PCB free power transformer oil donated by the power company? You are very lucky indeed. SCE here in SoCal is not so generous.

    Brian - K6BRN
  3. K6BRN

    K6BRN XML Subscriber QRZ Page

    Roger (G3YRO):

    Not everyone enjoys the hobby the way you do. Many of us experiment, build, test and repair gear, both radios and amplifiers. I have a variety of high power dummy loads and attenuators, for just this reason, all good to from 100W to > 1 KW, And they get pretty warm when I'm testing/repairing/adjusting/tuning an amp or rig, or experimenting with a new waveform. Not only do they provide a nearly perfect SWR, but they also prevent QRM and the inevitable complaints I'd get from the hours I usually spend doing this, if I were to transmit test tones into a live antenna.

    Brian - K6BRN
  4. KD2ACO

    KD2ACO Platinum Subscriber Platinum Subscriber Life Member QRZ Page

    So it's you!! :p:p

    I've seen single carriers upset many people... happens too often.

    I took a picture for K1ZJH but K7TRF beat me to it posting. It's been a couple years since I've dug down to the DL in my shop but it had a bit of oil on the top. Fortunately, the floor underneath it is fine and now it's sitting in a pie pan. There are good ideas around here daily.
    KA9JLM likes this.
  5. W1BR

    W1BR Premium Subscriber QRZ Page

    A second pint can for overflow in a sealed system like used for car radiators is starting to rise to the top of my list.
    KD2ACO likes this.
  6. KD2ACO

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    Keeping the resistor(s) submerged sounds like a good idea.
    One of the downsides of my MFJ load is that the resistor is mounted close to the lid so it could poke out of the oil over time and oil loss. I do have a little bottle of the same oil that went into it and it's probably time to top it up.
  7. KA9JLM

    KA9JLM Ham Member QRZ Page

    I smoked my Heath Cantenna resistor within seconds testing my 8877 amp.

    The oil never even had time to warm up. :eek:
    W1BR and KD2ACO like this.
  8. KD2ACO

    KD2ACO Platinum Subscriber Platinum Subscriber Life Member QRZ Page

    Sounds like a case for a more robust DL.
    Bigger toys for bigger boys! :p
  9. KA9JLM

    KA9JLM Ham Member QRZ Page

    That is true.

    Testing it at full power on a antenna will not fly, Roger.
  10. WA7PRC

    WA7PRC Ham Member QRZ Page

    So, we should use DLs that are rated only for exactly the power we're pushing into them or more power for only a few seconds. The parts to build my 1600W continuous load (link) were FREE scrapped from my employer. Otherwise, good deals on RF power resistors or complete DLs abound.

    It took a few calls to track down the transformer shop supervisor. He was most cooperative. The shop was yuuge (they serve a large customer base in my county) so, my SWAG is they use A LOT of oil.
    BrYan WA7PRC
    The Kanthal/Globar pn 886SP resistor (datasheet) is rated only 90W @ 40°C. The oil has a low thermal resistance and then, the heat needs to transfer to the surrounding air through the can. That's why it can't take a lot of power for very long. I now use my HN-31 for only low power stuff.

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