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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 Premium Subscriber QRZ Page

    What does MFJ, and what did the Heath Cantenna, use to provide for expansion relief in the oil filled loads?

    I have a load resistor and tapered line back dating back when Waters replaced load assembly in my 334 DL--they returned the old parts which was the entire load including the SO239. I picked up a shiny new gallon paint can figuring having an extra kW load around wouldn't hurt... but I am a bit stymied on a relief system that would not allow oil or vapor to escape. I like the Bird bellows system, but hard to adapt.
  2. K7TRF

    K7TRF Premium Subscriber QRZ Page

    Here's what the pressure relief looks like on my Ameritron dummy load. It's just a bit of brass tubing, just don't tip over the paint can ;)
    dummy load pressure relief.jpg
  3. W1BR

    W1BR Premium Subscriber QRZ Page

    Thanks, I guess I will scratch the MFJ approach... I expected too much :)
  4. KL7AJ

    KL7AJ Ham Member QRZ Page

    You will find that the ceilings of most hams of the era were dripping with transformer oil. :)
    Kitchens of the same era had ceilings dripping with the results of pressure cooked chicken cacciatore.
    WB7OXP and W1BR like this.
  5. W7UUU

    W7UUU Super Moderator Lifetime Member 133 Administrator Volunteer Moderator Platinum Subscriber Life Member QRZ Page

    Always a very good idea to keep a plastic tub lid or similar underneath the paint can - no matter what pressure system is used, there will always be "ooze" and if you value your floor, you'll appreciate the protection.

    WA7PRC and KP4SX like this.
  6. W1BR

    W1BR Premium Subscriber QRZ Page

    Bird oil loads do not leak. Waters loads didn't leak as a rule. I could always run it remotely outside... but if it blows up I'd miss the fun.
  7. KL7AJ

    KL7AJ Ham Member QRZ Page

    By the way....on a more serious note....when PCBs were used as transformer oil, there was never a worry about them catching on fire. On the other hand, "safe" mineral is highly flammable....almost higher temperatures. So much for progress.
  8. AD0AC

    AD0AC Ham Member QRZ Page

    But, you know, cancer sucks even more.
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  9. K1TGX

    K1TGX Premium Subscriber QRZ Page

    (4.2/10,000)*delta t (F) is the amount of expansion you get with mineral oil. So if you start at 60 deg F and go to 300 deg F you would get an expansion of (240*4.2)/10,000
    or approx 10% vol increase. A gallon is approx 231 cubic inches in volume so you would get ~ 23 cu in of expansion. If you filled the 'bucket' to 80% capacity the pressure would more than double under these conditions. OR you could silver solder a piece of 3/8 od soft copper tube to the lid and connect it to an 'expansion tube'. The expansion tube could be a sealed 12" piece of 3" copper tubing or steel nipple capped on both ends with provision to attach the 3/8 od tubing. Little chance any real pressure will build up before the lid just pops.
  10. W1BR

    W1BR Premium Subscriber QRZ Page

    Well, I happen to have 3" cu tubing and some heating oil cu tubing, so I could do so, but doubt I'd want to let it get that hot. Too close to its flash point. Good suggestion.

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