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DUMMY LOAD ADVICE




 
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W2PFY
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« on: April 01, 2020, 09:32:16 AM »

What’s a man to do now that most 100-watt bulbs have disappeared from the store shelf's?
In the past whenever I needed to test a low power rig or a medium powered rig, I would use an off the shelf bulb and if I needed more capacity than a single 100 watt bulb, I would just purchase more 100 watt bulbs and wire them in series parallel as necessary to get the job done. Inasmuch as I have the load test bank already built with all the sockets and switches mounted on a board, I could see no reason to switch over to a resistor bank or some new solid state design but, the problem I am having is that the LED replacement’s I purchased are only 12.5 watts each requiring about eight such bulbs to get the same wattage rating of 100 watts. As you can probably see the cost is way up there too with these LEDS at about $8.00 each bulb or about 64 bucks for just under 100 watts. Now if I want to go up to let’s say, 500 watts of dissipation, the cost is  way high and I’ll need 40 bulbs at 320 bucks and I had to buy more sockets at Home Depot at 12 bucks each, for an additional cost of $382.00 or about $682.00 for the new load bank.

Ok, so I got that build out of the way but now I am having a problem with RF and using LED’S as a dummy load. It seems that some light up and others don’t, some blink on and off at a very rapid rate while others are giving off a funky color and to top that off, they are causing TVI to my Plasma TV!  The inline RF ammeter sometimes reads correctly and at other times without explanation, the meter pins itself!

Any idea what the problem could be here. Do I need a tuned throughput circuit or something? Possibly matched LEDS? RFC chokes installed on the transmitter filaments, Vacuum capacitors in place of the electrolytic’s?

I am about to give up on this project so any suggestions you may have will be helpful no matter how silly they may sound!

Puzzled to say the least!

Future projects = Oiled cooled cigar holder. Moose restraints. Cement chewing gum.



 
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W1ITT
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« Reply #1 on: April 01, 2020, 10:14:04 AM »

Light bulbs were an imperfect solution at best, although most of us have done it at least once out of financial necessity.  And with these cussed LED bulbs the problem gets worse.

https://www.ebay.com/itm/Lot-of-2-Carborundum-Co-888-SP101K-Non-Inductive-Resistors/293364980305?hash=item444dea5a51:g:3fgAAOSw2wZd6qGS

Here's an Ebay example of Carborundum resistors, a pair of 100 ohms units that would make a swell 50 ohm load either in free air, or in front of a blower, or swimming in mineral oil.  Years ago I worked for an RF components company and we made, among other things, "air blast loads".  These were series-parellel combinations of Carborundum resistors sitting above a large high volume blower.  Ours had good SWR characteristics up beyond the FM band, where most of them went, without any special matching techniques.
You can find other combinations of resistance and dissipation capability, on Ebay and sometimes at outlets like RF Parts.  Another possibility is large arrays of big-ass SMD resistors.  But it's time to ditch Edison based bulb solutions.

73 de Norm W1ITT
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WD8BIL
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« Reply #2 on: April 01, 2020, 10:17:55 AM »

I think you've been locked up too long, Terry!

But ifn you're gonna spend $100 on light bulbs why not just buy one of those paint can dummy loads? MFJ has one for @$72.

https://mfjenterprises.com/collections/ameritron/products/adl-1500x?_pos=5&_sid=5de405195&_ss=r
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« Reply #3 on: April 01, 2020, 10:32:37 AM »

Hey Terry ..

Obviously, you’ve been using the “Edison Factor” for your go-to dummy for a long time!

I get it, we all get comfortable with things that work for our set-ups.
 However, just a quick search online and you can get a 4-pack of 100 watt incandescent bulbs for $1.80 !


https://www.lightingsupply.com/ge-100a-sw-4pk-120v.aspx?gclid=EAIaIQobChMIieGb47HH6AIVy4CfCh2Lrgt8EAQYASABEgKpwPD_BwE

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« Reply #4 on: April 01, 2020, 10:37:18 AM »

I agree with the others, the paint-can dummy load or resistors,etc.
Light bulbs DO work and you can shield them, and you can buy them in high power versions also,etc.
But why bother when we have simple solutions.
I bought the MFJ "non-inductive" 200 watt "Continuous duty" Resistor , (not the 10w for 10 seconds types)
I built my own shielded box, its worked fine for a couple years now (no oil needed).
The oil types of course greatly increase the cooling, as does the type of oil. (see the chart on the old Heathkit oil-can)
When I was looking up specs on the Non-inductive resistors they said some are made for submersion in oil,
but some are NOT, so make sure before you dip them in oil.
You'll find a simple sulution that works for you, good-luck,
73's
AG5UM

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KB2WIG
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« Reply #5 on: April 01, 2020, 10:58:37 AM »




As others have said, you can still find the incandesents.... i have an old 500 Watt "construction'" flood light. Replacement lamps are still available,( 300 W too).  Walley Whirl carries 200W Edison base, in store, last time I checked.

I broke down and bought a Bird 500 W  continuous dummy load ( Bird watts are the best watts).
This thing looks like it will take a lot more for a  reduced  duty cycle.

KLC

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« Reply #6 on: April 01, 2020, 11:58:49 AM »

Terry,


In case you missed it last January, here's a 900 watt floodlight dummyload I built after I fried my bird load. (nine 100 watt floodlights in series / parallel)

The bulbs are cheap.  I use it quite often and haven't blown any bulbs yet at 375 W carrier, 1500 W pep.


I had all the parts just lying around so was an easy choice:

http://amfone.net/Amforum/index.php?topic=45547.0


* Jeff/ NBC's  100 watt bulbs deal posted above for $1.80 each is a great option too.     Also, Buddly's MFJ dummyload.


T
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« Reply #7 on: April 01, 2020, 02:34:42 PM »

Reminds me of when I was experimenting with arc-5 transmitters.  I was using a light bulb as a dummy load, however, the variable load as the lamp goes on and off would make a stock arc-5 cluck like a chicken.  A 12a6 or 6ag7 isolation stage between the vfo and final would completely remove the clucking.  The effect of the isolation stage was impressive.  Those building homebrew transmitters might think of using a light bulb to check vfo isolation.
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« Reply #8 on: April 01, 2020, 03:29:28 PM »

How about this?

https://www.ebay.com/itm/Microwave-RF-High-Power-Dummy-Load-500W-1-GHz-N-Type-50ohm-DC-1000MHz-TESTED/272977252727?hash=item3f8eb65177:g:d14AAOSw3fZaLXnx
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« Reply #9 on: April 01, 2020, 05:40:48 PM »

I purchased my load from a company in Texas, Tucker Electronics.  It's a single 1000 Watt carbon resistor in a 35 gallon drum filled w transformer oil.

I have put ungodly amounts of power through it....  Tetrodes with handles.

Since the heathkit is a 50 watt ccs resistor, this one has to be good for a lot.

Tucker stated they used it to test Collins 208U-10 units before offering them for sale.


Norm, your description sounds like my old Altronics unit.  It was a 50Kw CCS. Quite a few resistors in series / parallel.  I got it from an AM station that shut down.


To the OP, i get that it is April 1st....

--Shane
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W2PFY
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« Reply #10 on: April 01, 2020, 06:55:07 PM »

 Grin
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« Reply #11 on: April 01, 2020, 08:13:21 PM »

If u must have 100 watt bulbs, try 100 watt *130* volt rated A19 lamps. They're still available and cheap. They are rated at 130 volt and a slightly higher resistance. They still make these. No difference for what u want to do. U might have to buy a pack of 4 to get one. ST KC2WE
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Seth Taylor
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« Reply #12 on: April 04, 2020, 08:36:01 PM »

Terry -

Dollar Tree sells incandescent light bulbs.

You can also scrounge thrown out stoves/ovens for the elements.
The oven elements will have not much inductance.
Stove elements might have too much at 28mhz, but probably not.
Haven't measured the DCR, but since they're free, you can series up
all you need! Cheesy

If you have an electric stove, pretty easy to pull an element and check it.

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MikeKE0ZUinkcmo
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« Reply #13 on: April 05, 2020, 02:46:41 PM »

...or buy a couple of these 100 Watters for ten to fifteen bucks each, and screw'em to an old stereo heat sink.

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« Reply #14 on: April 05, 2020, 04:29:20 PM »

...antennas work too.

Jon
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« Reply #15 on: April 05, 2020, 05:46:14 PM »

Make friends with your local TV broadcaster. With the television repack most TV broadcasters have literally tons of junk like combiners and Mask filters that are just about useless in today’s world. Remember that any TV transmitter above channel 40 including all its RF combiner and Mask filter are never going to be used again.
All constant impedance Mask filters had small dummy loads in the 500 to 2 or 3 kW size as reject loads and the combiners in solid-state transmitters were around the same size.
I have seen stack of the loads saved and the filters sold for scrap. Just try to ask the people in engineering directly and who knows you may end up with more then you can use for a small donation to the engineering lunch fund.
Just don’t ask the management or sales people in your typical station because they will want all they can get!
In the last ten years or so we have killed off analog TV, now the first generation of Digital TV transmitters and most transmitter sites are littered with all that stuff that has no resale value that often is free for the taking. You just got to talk to the right people.

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« Reply #16 on: April 05, 2020, 10:29:46 PM »

...antennas work too.

Jon


Joking, right?
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VE7RF
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« Reply #17 on: June 25, 2020, 01:58:24 PM »

...antennas work too.

Jon


Joking, right?

Yes, ants  work  good, but with some caveats.
160m  at high noon...and  10m  at  midnight.

On a more serious note, be careful with older style  globars.  The CX series were NOT designed to be immersed in oil.
These older CX style  were  12"  long x  1"  diam, and a good  1/4"  thick.  200 ohms each, and 4 in parallel, for an air cooled
DL, inside a cage.    IF they are installed in oil, they will absorb the oil, and resistance will  skyrocket. ( per eng lady I spoke to at globar)

I have 4 of the new style  globars, that are shiny on the outside, designed for oil (or air).  These are  SP  types.  (12" long x  1" diam, 375 watt rated).   Had a ham buddy heliarc weld  4 x  aluminum pipes together,  with  1 resistor  dead center, down the inside of each tube.   The  4 x pipes  are suspended from the lid of a new 5 gal paint can.  Can was not tall enough, so  bought 2 of em,  and  cut the lip off one of them, then brazed  together..to add some height.   So it's  now  7.5 gallons.  Installed  a  7-16  din connector dead center on lid.   Filled with xfmr oil...plus a small pressure relief on outer edge of lid.

It amounts to  a hb  heath style  DL  on  steroids.   Other schemes  include the AG6K  hb  water cooled DL.   Single 50 ohm, type sp resistor inside  4"   PVC  tube, with end caps and  3/4"  garden hose fittings.  It's  still  on  ag6k's  website.

The simple heath /  mfj   1 gallon  of oil  is effective, just don't  over do  it.   The resistor inside is  only rated at 90 watts..and is  5"  long  x 3/4"  diam.

9  of the  50 ohm caddock style  in  series parallel also work good.   3 x rows, with 3 in series in each row.  Mounted to a massive  al heatsink.

Jim  VE7RF
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« Reply #18 on: June 25, 2020, 03:56:08 PM »

On Amazon "CEC Industries TS100 (Frosted) Silicone Coated, Rough Service Bulbs, 130 V, 100 W, E26 Base, A-19 shape', about 11 bucks for six. Why are they stiall available? They're rated at 130 volts instead of 120. So they're treated as an energy saving bulb when run at 120 volts. In industrial use, they are used as a substitute where only incandescent will work. Sometimes, local electric supply stores will have them. 


* bulbs.jpg (9.42 KB, 302x320 - viewed 4 times.)
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« Reply #19 on: June 25, 2020, 05:15:40 PM »

Incandescent bulbs will be starting up cold at about 1/20 the desired load résistance, tube transmitters can handle this start-up, but I doubt a solid-state transmitter can.  Like many others here, I've run light bulb dummy loads on tube transmitters but never did with a solid-state transmitter, used Bird loads.
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« Reply #20 on: June 25, 2020, 07:43:38 PM »

1000bulbs.com
88 cents all day and night.
130V 100W

https://www.1000bulbs.com/category/100-watt-standard-shape-light-bulbs/


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« Reply #21 on: June 25, 2020, 08:46:45 PM »

The  130 V rated bulbs  have slightly higher hot resistance.   I will have to dig up some old notes,
but I  think the  cold  resistance  was  either  1/10  or  1/12  the hot resistance.   Never tried
light bulbs  with  SS  xcvr's,  only  100w  tube  rigs, and that was a long time ago.

I also designed this  elaborate scheme, where the oil  was  pumped  externally through an air cooled radiator,
then re-circulated back to the can of oil.  Per some e-mail  with kanthal /globar,  with oil externally cooled,  the
CCS  ratings  of the  DL  resistors can be increased  by  5X.   I dumped the concept  after I had a small leak, and
ended  up with a small mess  on the concrete floor in the workshop.   That plus an external  radiator has to be shrouded,
so the airflow from  any fan can be done correctly.

Even with 2 x  new  5 gal paint cans  brazed together, we had to  re-braze in 2 places.  (we tested  for leaks by using water).

What I really need is a small 10 gal  steel drum..and mating lid.   I have looked everywhere  and have had no luck.   Everything is plastic these days.  ( what might work is the container that real small pole pigs go into, I believe pole pig xfmr's are in  aluminum  containers) ?

Sure, ants are fine.... but I don't have ants  for all  10 bands.  I need the DL to test the hb linears on all bands.

Still yet  another  scheme is  the saltwater loads.  A rod  from lid mounted coax connector is  run  straight down  into the container.  Salt is added, till  DC resistance  drops to  50 ohms.   How long that holds out, till  corrosion sets in, is  anybody's guess.

Jim  VE7RF
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« Reply #22 on: June 25, 2020, 10:03:13 PM »

oven broiler elements....  even some electric range circular elements are very close to 50 ohms and will handle high power

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« Reply #23 on: June 25, 2020, 10:53:33 PM »

Buddy across town  got the  DL  from an  AM  station that had shut down (they  all  switched to  FM).
It  consisted of a   series-parallel myriad of  clothes dryer / oven eles,  built into a rectangular box frame, with a huge fan on the bottom.
It looked very similar to the  dummy loads we used at the Telco I worked at for  34 years.... but the telco  DL's were used
for load  testing emergency generators.....up to  500 kva..( and coils could be switched in /out in parallel  with a tap switch, to change the load).

The  AM  DL had an adjustable vac  cap (+ fixed  vac padders)  across the  50 ohm input.  The Xc of the cap assy  was used
to tune out the  XL of the   clothes dryer /oven ele assy.  I  dunno how high in freq you can get  away with that scheme.  It came with
an  EIA  flange  connector, so no easy way to test  with ham gear.  The variable cap /padder assy had to be manually tuned for whatever freq the  AM  broadcast  station was on.  Once adjusted, it was never touched for 45 years.  For ham use, it would have to be tweaked a bit from band to band.    It was simply  too big for my use..and nowhere to install it.   But the concept could be scaled down for  50 ohm ham use.
With  my luck,  I'd  end up  burning the basement shop down. 

The  heating / drying ele in a dishwasher is good for  1.5 kw.... and is immersed in water.  Used to top up the water temp to  140 F..and also used to fast dry  wet dishes.   So they can be operated  dry..or  wet.

Jim  VE7RF
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« Reply #24 on: June 27, 2020, 06:36:40 AM »

I lit up a lamp with my first BC-696 ARC-5 Transmitter. But it was the lamp my dad was using to read the paper downstairs!
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