The AM Forum

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.



 

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

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 (https://mfjenterprises.com/collections/ameritron/products/adl-1500x?_pos=5&_sid=5de405195&_ss=r)

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

“We’ll keep the light on for yah”

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

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

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

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.
Remember what Moe said, "Spread out!"

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 (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)

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
KD6VXI

 ;D

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

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! :D

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

                    _-_-bear

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

(https://photos.smugmug.com/Miscelaneous-/BIGGIES/i-SJGTx5c/0/93726316/L/TO-220%20CaddockResistors-L.jpg)

...antennas work too.

Jon

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.

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

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. 

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.

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

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

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

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

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

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!

Were those Avtron loads? We used them at Lorain Products to test the telcom power systems! My lab had enough load banks to pull 15,000 amps at -48VDC!

##  Nope, these loads were for the   208/120 vac  (3 phase)  diesel generators  that  each  Central office had.   The cell sites (only a few of the bigger cell sites  had an emergency generator) ran on  240/120 vac,  single phase, like a home.  The fan on the portable  DL  made a hell of a racket. It was towed behind a truck.

##  Main office  downtown,  was  470 / 271 (3 phase).

##  we only had small DL's  for the  +5vdc (@ 40A)  supplies.   These were  DC-DC  converters, thousands of them. -52 vdc  input..and  +5Vdc output.

##  Think it was around late  70's, when the change came to the  -48 vdc.  It was increased to  -52 vdc.  It's  still  -52vdc to this day.

##  Never did see a  huge  dummy load for the  -52 vdc  rectifiers.  The  -52 vdc rectifiers  came in  25-50-100-200-400-800  amp  sizes.
Huge things in the  400 +  800 amp sizes.   Before I retired in  2009, the  new standard  was the -52 vdc switching type  supplies.   6 x 3.3 kw  units in one  shelf (20 kw /  400A  ccs)...that ran on  208 single phase....  or  240 vac  single phase  (cell sites).  Up to 7-8  shelves in a bay..with a control unit in the middle of the mess.  One bay was good for  140-160 kw.

##  Main office  downtown  sucked  3750 Amps @  -52 vdc.   We bought the power from the power  company at 14.4 kv / 3 phase...  then had our  own 2000 kva  vault  transformer  ( to step it down to  470/271 vac).   The emergency generator on the roof  was 1800 kva, and was a V-16  diesel. 2 x 35,000  litre  underground ( double walled) diesel tanks below the parking  lot.  Fuel lines were the size of fire hoses.

##  We had a myriad of  Lorain products in most offices.  Extremely rare we had issues  with Lorain equipment.

##  On  a side note, apparently the large dummy loads can be rented.  A  buddy had  400 A  (240/120) service upgrade to his home.  The power company wanted to install a 2nd  50 kva  xfmr in parallel  with the existing  50 kva xfmr.....and still feed  9  homes.   Buddy  complained, and they relented,  so the new xfmr is just for his home.   Now the battle is.... a new, dedicated  50 kva  xfmr is only good for 200A, not  400A  !   So he's gonna  rent a  DL,  suck  400A  CCS, and destroy the new xfmr.  Then he will get a 100 kva installed.

## I have  '200 A'  service into my home... but the  50 kva  xfmr is  shared  with a total of  9  homes.  (5.5 kva  per home).   Power company guys came out..said  to just blow it up ( they are over fused  with a 9-11  amp  slow blow).  They said they  have em in  25-50-75-100-125  kva  sizes ( for mounting on utility poles).  They can also be paralleled.  Anything bigger, and it has to be mounted on the ground, on a slab, inside a kiosk.

##  silly really.  My 3-0 cu wire from  200A  panel is spliced into 2-0 Al  drop line ( it might be  1-0 al).   V drop  from xfmr  to B+  supply is bad news.   Once these  100%  electric cars become more mainstream, the  pole pig xfmrs will  start popping offline, massive upgrade required.

sri for the  diatribe.

Jim  VE7RF

The utility company doesn't have to comply with NEC regarding utility drops to a house. Silly, really.

And So Cal Edison.... What a hoot.  Friend built a house and had to have a new drop to his house.  Goes to engineering, they recommend a new xformer.  He buys a pole pig through SCE, they mount it run service drop to his pole in his property, etc.  75kva as he plans in having a shop w welder, etc.

NO GUARANTEE THEY WON'T CONNECT OTHERS TO HIS PIG!  Even though he purchased it, paid to have the service installed, etc.  It's a shared transformer.

You have to purchase wholesale power to get your own xformer!

I've heard the dame story about having to blow a pig up before they will replace it.

Me, I want 208/120. 

--Shane
KD6VXI

Hi folks, I cannot believe the traction this tread has attracted and the good suggestions that have come from it considering that it was supposed to be an April 1st. spoof. I guess I cannot do it as well as the ARRL has done in many of their publications?

Anyhow lets keep it rolling!     

Shane, did u get the pix I sent u ?

Back to  50 ohm  DL's.   Instead of oil, can  distilled water be used instead ?   IE: if a new / clean  heath /mfj  1 gallon can is filled with
distilled  water,  will it still be  50 ohms resistive   up to  30 mhz ??   What about plane tap water ??   As long as swr stays flat  ( even when  hot),  it occurred to me that  my hb  DL  could be filled with distilled water, instead of oil.  ( it's  empty and clean right now).

I ran through the various formulae, and even with "power level X"  it would take a while to heat up  7 gallons of water, esp with pulse tuning at  30%  duty cycle.

Another thought is to  attach 3/4" garden hose brass  fittings, etc... to lower end of side of 7 gal container..and also upper  end of same container ( but  opposite side).  Then just crank in cold tap  water into bottom portion of  7 gal can....and   route the  hot water  from  upper fitting....over to a drain.  The idea here is... once  7 gallons  get hot, it takes a long time to cool down, esp  oil..which could screw up any   RF testing.  In those cases, the cold tap water could be used to  cycle through the can.   Coaxial  dynamics 15 kw  water cooled load  uses  4 GPM..and plane jane  3/4" garden hose fittings. (  2 GPM on their 5 kw loads).  Coaxial dynamics  uses  3/4"  garden hose fittings.

Jim  VE7RF

Excellent PDF  from  coaxial dynamics.  Everything you ever wanted to know about their  water cooled loads.  They all use  3/4"  garden hose fittings.   Water  goes down the INSIDE of the  tubular  50 ohm resistor ( bottom  end of  resistor, where it's  shorted)... then  comes out the top of the resistor,  loops around,and then makes a 2nd pass, but this time  down the outside of the resistor.... back to the bottom, then exits the DL,  through  3/4"  garden hose fitting  #2.

http://www.coaxial.com/manuals/86000.pdf

The above is fine..as long as you have loads of municipal /  city  water..and it all goes down the drain ! 
For Broadcast sites out in the bush, etc, this is  not feasible, so  either a reservoir is used  (200-1500 gallons)...or an external ( air cooled ) radiator  is used.

One big advantage of water is....  if something leaks, or gets spilt on my  concrete basement shop floor, I don't end up with a helluva mess,  unlike  oil !

Jim  VE7RF

AM Load here.   FWIW  Vic