• You can now help support WorldwideDX when you shop on Amazon at no additional cost to you! Simply follow this Shop on Amazon link first and a portion of any purchase is sent to WorldwideDX to help with site costs.

Metal oxide resistors for dummy load in oil - do they last?

ShakyMcQuiver

Active Member
Apr 11, 2018
69
57
28
Anyone ever used these metal oxide (flame proof) resistors in a mineral-oil type of dummy load?
I've used this type of resistor in simple dummy loads, but never in one that's been submerged in oil.

While foraging around in my boneyard of parts, I found some copper pc-board and several of these 1k, 5 watt resistors and thought about making a larger dummy load and put it in a 1-quart or 1-gallon can and fill it with mineral oil. I think I have enough to make a 100-watt load (20 I think if my math holds).

I'm curious how they'll hold up? Anyone know?

1663827856201.png
 

Attachments

  • 1663827810734.png
    1663827810734.png
    181.8 KB · Views: 76

Just for reference, the resistor in the Heathkit Cantenna is a 50 watt unit. Submerged in oil it was rated/able to handle 1000 watts intermittently.
 
Just another way to provide some additional heat sink. I cut the tops and bottoms off two appropriately sized tin cans that would tightly sandwich all the resistors between them. By first laying all the resistors out like spokes on a wheel, a mark was made on the cans where each resistor lead was mounted. A small drill hole was made for each lead to fit through and later soldered. I like to think of it like a wheel, where the outside can is the tire and the smaller can is the hub. This structure can now be hung inside an even larger can with the hub connected to the center conductor and the tire connected to shield or ground. No problem handling 100 watts, at least with short bursts.
 

Attachments

  • IMG_20220922_164225524.jpg
    IMG_20220922_164225524.jpg
    934.7 KB · Views: 90
  • Like
Reactions: tecnicoloco
I have some large old school classic 50 ohm brown ohmite units witht he silver plated ends that 50,60,100 watt units. To easy to build those into an empty paint can. I think I bought all of them a few years ago off ebay for under $10 each

The modern units sp5it mentioned are great as well as compact. Plenty of people use jelly bean resistors in series and parallel forever to do what they need.

I like the idea of fewer parts to get to desired wattage and resistance. The more parts you have to use to reach a goal the more failure paths you create. How often do we check our dummy loads? Unlike some of my hand tools that have certification seals on them that are out of date none of my electronic tools are certified because I do this for fun.

So I prefer to use fewer components every time I can. I understand being frugal and making due as well. I absolutely hate it when I see some of they amps today that have those nasty blue Chinese caps and they have 5+ caps when it really is crying for 1 appropriate cap. Clearly there are many ways to skin a cat fish! It all comes down to acceptable risk and cost to benefit ratio.

There are a lot of designs on ebay that use metal film resistors in combination to get to 50ohm load and about 60 watts.
 

dxChat
Help Users
  • No one is chatting at the moment.
  • @ Wildcat27:
    Hello I have a old school 2950 receives great on all modes and transmits great on AM but no transmit on SSB. Does anyone have any idea?
  • @ ButtFuzz:
    Good evening from Sunny Salem! What’s shaking?
  • dxBot:
    63Sprint has left the room.