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All:
A number of you have written me privately saying you're having trouble finding the 1K 3W resistors for the dummy load project (Nov., 2018, QST). If you don't have access to QST, you can download the assembly manual from our site:
Evidently, some eBay suppliers say they have them, but the order quickly becomes a back order. Check before you order. Someone just wrote to me and said Arrow carries them:
but they are saying a December delivery. I bought mine from Rich at communications-lab.com:
You may want to write first, as he was moving his business to HI when we last spoke. Also, if you know that you're always going to be using QRP power levels, you could cut back on the wattage and that should make them easier to find (and cheaper).
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Mouser has 2,837 of the 1k 3W Xicon in stock, item number 283-1.0K-RC
They don't really have to be 1k, there are plenty of other choices.
For example, get the same part at 1.2 k, item 283-1.2K-RC
and use 1200/50 = 24 of them in parallel instead of 20.
If all you ever expect to feed it is 18 watts or so, maybe use 300/50 = 6 of? ?283-300-RC
You wouldn't even need that oil bath, just good air flow.
Other values that might? be of interest:? 51? 100 150 200 300 510 750
Jerry, KE7ER
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On Sat, Oct 27, 2018 at 07:53 PM, Jack Purdum wrote:
A number of you have written me privately saying you're having trouble finding the 1K 3W resistors for the dummy load project (Nov., 2018, QST).
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Another path to take, if you already have a 50 ohm dummy load, is to use that instead.? You will need to calibrate the system in that case.
I am working on a version of the DDL using a SparkFun, Microview module in place of the Arduino board and display and an MFJ, 300W Dry Dummy Load.? I am also adding a Peak power function to the sketch and a bootup option to enter the reference power reading and have the system self-calibrate.? It is in the 'breadboard' stage at this time and I will post the code, etc. when I have packaged it up and tested it in that form.
Dennis KG4RUL
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Great idea! Seeing others experiment with ?C's in projects is terrific!
Jack, W8TEE
On Sunday, October 28, 2018, 7:38:35 AM EDT, Dennis Zabawa <kg4rul@...> wrote:
Another path to take, if you already have a 50 ohm dummy load, is to use that instead.? You will need to calibrate the system in that case.
I am working on a version of the DDL using a SparkFun, Microview module in place of the Arduino board and display and an MFJ, 300W Dry Dummy Load.? I am also adding a Peak power function to the sketch and a bootup option to enter the reference power reading and have the system self-calibrate.? It is in the 'breadboard' stage at this time and I will post the code, etc. when I have packaged it up and tested it in that form.
Dennis KG4RUL
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Here is a power resistor I used in another dummy load. These could be an alternative if the ones specified for this project are hard to find. I used two on a heatsink. Possibility in oil the wattage these can handle would be increased. The small heatsinks attached, while in the oil would likely help.? Tom, wb6b 
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?I ordered far too many of the 1K/3W resistors for this project.? I've enough of the passive components plus D1(BAV21) for four additional builds.? ?I've made up four kits consisting of 20 1K/3W, 1 56k, 2 1k (don't have 2k in my box)? resistors, D1 and C1 (50V--ok for QRP, but if you want the 150W version you should replace with a 250-500V as specified).? Drop me a private email if interested.?
John
WI6P
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I still have three sets of components as described....$10 includes postage.
73
John
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Mouser used to sell Xicon 3W metal oxide resistors in small quantities, now they have a minimum buy of 100 at $0.10 each.? Darn!?? ? 283-100-RC?? ? ? ? $0.10/100 But they do have a KOA-Speer in single units, haven't gotten any but they look good: ? 660-MOS3CT631R101J? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? KOA Speer? ?3W radial metal oxide,? $0.20/1? $0.15/100 Tayda has a no-name product at $0.06 each with single unit pricing, ? SKU A-2549? ? ? $0.06/1 Those are all 100 ohm, two in parallel from Tayda at $0.12 should be suitable for use with a uBitx. 20 of the 1000 ohm variant in parallel are 1000/20=50 ohm, good for 20*3=60 Watts continuous. Also some offerings in metal oxide resistors at 2 Watts instead of 3 Watts. If you want to spend more than $0.12, here's some proper RF dummy loads for 100W or more at under $10: ? ?? ? ? Will need a good heat sink and thermal paste for those guys. Search for "RFP Dummy Load" to find other options. To spend less than $0.12 and have it working today, check out WB9SBD's baking soda bath: ?? /g/BITX20/message/83207Jerry, KE7ER ?
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We did a similar DL for the November 2018 QST article which also had a watt meter built in. By putting the resistor pack in mineral oil, we were able to run 200W into it for 5 minutes without failure.
On Saturday, October 31, 2020, 10:43:28 AM EDT, Jerry Gaffke via groups.io <jgaffke@...> wrote:
Mouser used to sell Xicon 3W metal oxide resistors in small quantities, now they have a minimum buy of 100 at $0.10 each.? Darn!?? ? 283-100-RC?? ? ? ? $0.10/100 But they do have a KOA-Speer in single units, haven't gotten any but they look good: ? 660-MOS3CT631R101J? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? KOA Speer? ?3W radial metal oxide,? $0.20/1? $0.15/100 Tayda has a no-name product at $0.06 each with single unit pricing, ? SKU A-2549? ? ? $0.06/1 Those are all 100 ohm, two in parallel from Tayda at $0.12 should be suitable for use with a uBitx. 20 of the 1000 ohm variant in parallel are 1000/20=50 ohm, good for 20*3=60 Watts continuous. Also some offerings in metal oxide resistors at 2 Watts instead of 3 Watts. If you want to spend more than $0.12, here's some proper RF dummy loads for 100W or more at under $10: ? ?? ? ? Will need a good heat sink and thermal paste for those guys. Search for "RFP Dummy Load" to find other options. To spend less than $0.12 and have it working today, check out WB9SBD's baking soda bath: ?? /g/BITX20/message/83207Jerry, KE7ER ?
-- Jack, W8TEE
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Yup, this is your thread.
Started two years ago with regard to the QST article.
Jerry, KE7ER
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On Sat, Oct 31, 2020 at 08:08 AM, Jack, W8TEE wrote:
We did a similar DL for the November 2018 QST article which also had a watt meter built in. By putting the resistor pack in mineral oil, we were able to run 200W into it for 5 minutes without failure.
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Good grief...didn't know!
Jack, W8TEE
On Saturday, October 31, 2020, 11:31:38 AM EDT, Jerry Gaffke via groups.io <jgaffke@...> wrote:
Yup, this is your thread.
Started two years ago with regard to the QST article.
Jerry, KE7ER
On Sat, Oct 31, 2020 at 08:08 AM, Jack, W8TEE wrote:
We did a similar DL for the November 2018 QST article which also had a watt meter built in. By putting the resistor pack in mineral oil, we were able to run 200W into it for 5 minutes without failure.
-- Jack, W8TEE
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I have been using these for my dummy loads and they have been pretty darn surprising.
https://www.aliexpress.com/item/32966376132.html?spm=a2g0o.productlist.0.0.1a9e5261YmP5gm&algo_pvid=d2007a98-6b86-4a1d-80ce-61348dbc4deb&algo_expid=d2007a98-6b86-4a1d-80ce-61348dbc4deb-9&btsid=0bb0622d16041657591331983eada4&ws_ab_test=searchweb0_0,searchweb201602_,searchweb201603_
--
David
?N8DAH
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David:
If you just use 32966376132 in the Ali search bar, it finds the item.
Jack, W8TEE
On Saturday, October 31, 2020, 1:37:56 PM EDT, N8DAH <dherron@...> wrote:
I have been using these for my dummy loads and they have been pretty darn surprising.
https://www.aliexpress.com/item/32966376132.html?spm=a2g0o.productlist.0.0.1a9e5261YmP5gm&algo_pvid=d2007a98-6b86-4a1d-80ce-61348dbc4deb&algo_expid=d2007a98-6b86-4a1d-80ce-61348dbc4deb-9&btsid=0bb0622d16041657591331983eada4&ws_ab_test=searchweb0_0,searchweb201602_,searchweb201603_
--
David
?N8DAH
-- Jack, W8TEE
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Looking at David's aliexpress listing, it says they are "carbon film".
A google search of "carbon film vs metal film" says metal film is more stable, if that matters.
And says there's lots of variation between manufacturers.
I believe both carbon film and metal film get trimmed to a final resistance value
with a spiral laser trim, adding an inductance that is not defined in the datasheet.
Inductance will vary with batch, depending on how thick the film gets deposited.
So ideally, we would find a quality product, characterize it thoroughly, and stick with it.
Better yet, buy those dummy loads purpose built for microwave frequencies.
Jack's QST article used 3W metal film resistors.
I've used a parallel set of twenty 1K ohm 3W Xicon brand metal film resistors
as a dummy load with good luck.? My nanovna shows a Smith Chart through 30mhz
with a single dot at the center, and still reasonably good at 144mhz.
Most of the inductance shown is likely in the relatively long leads I have.?
Next time I place an order for Tayda or Mouser, I'll buy some 100 ohm 3W resistors
and see what the nanovna thinks of them.? But I suspect they will work well enough.
Regarding the URL:
It's usually possible to strip off their tracking information from these ridiculously long URL's.
In this case, everything from the '?' on out to the end:??
For Amazon, everything from the "/ref" on out to the end.
Jerry, KE7ER
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On Sat, Oct 31, 2020 at 10:51 AM, Jack, W8TEE wrote:
If you just use 32966376132 in the Ali search bar, it finds the item.
?
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Good info. But when you build one of those in the image, I suggest that you leave the leads long since they help dissipate the heat.
Bob ¡ª KK5R
On Saturday, October 31, 2020, 11:08:39 AM EDT, Jack, W8TEE via groups.io <jjpurdum@...> wrote:
We did a similar DL for the November 2018 QST article which also had a watt meter built in. By putting the resistor pack in mineral oil, we were able to run 200W into it for 5 minutes without failure.
On Saturday, October 31, 2020, 10:43:28 AM EDT, Jerry Gaffke via groups.io <jgaffke@...> wrote:
Mouser used to sell Xicon 3W metal oxide resistors in small quantities, now they have a minimum buy of 100 at $0.10 each.? Darn!?? ? 283-100-RC?? ? ? ? $0.10/100 But they do have a KOA-Speer in single units, haven't gotten any but they look good: ? 660-MOS3CT631R101J? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? KOA Speer? ?3W radial metal oxide,? $0.20/1? $0.15/100 Tayda has a no-name product at $0.06 each with single unit pricing, ? SKU A-2549? ? ? $0.06/1 Those are all 100 ohm, two in parallel from Tayda at $0.12 should be suitable for use with a uBitx. 20 of the 1000 ohm variant in parallel are 1000/20=50 ohm, good for 20*3=60 Watts continuous. Also some offerings in metal oxide resistors at 2 Watts instead of 3 Watts. If you want to spend more than $0.12, here's some proper RF dummy loads for 100W or more at under $10: ? ?? ? ? Will need a good heat sink and thermal paste for those guys. Search for "RFP Dummy Load" to find other options. To spend less than $0.12 and have it working today, check out WB9SBD's baking soda bath: ?? /g/BITX20/message/83207Jerry, KE7ER ?
--
Jack, W8TEE
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Found it here:
But, what value did you use and what value?
K4EAA offered a set of resistors that I used in a Lowes empty quart can and mineral oil that had a banana jack and a bridge that you could use with a multimeter and calculate the power out into the dummy load. My main dummy load. If he responds to my message, I will post here.
Bob ¡ª KK5R
On Saturday, October 31, 2020, 1:51:13 PM EDT, Jack, W8TEE via groups.io <jjpurdum@...> wrote:
David:
If you just use 32966376132 in the Ali search bar, it finds the item.
Jack, W8TEE
On Saturday, October 31, 2020, 1:37:56 PM EDT, N8DAH <dherron@...> wrote:
I have been using these for my dummy loads and they have been pretty darn surprising.
https://www.aliexpress.com/item/32966376132.html?spm=a2g0o.productlist.0.0.1a9e5261YmP5gm&algo_pvid=d2007a98-6b86-4a1d-80ce-61348dbc4deb&algo_expid=d2007a98-6b86-4a1d-80ce-61348dbc4deb-9&btsid=0bb0622d16041657591331983eada4&ws_ab_test=searchweb0_0,searchweb201602_,searchweb201603_
--
David
?N8DAH
--
Jack, W8TEE
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This is a little off the topic but I have a 100 watt dry load from MFJ. Can I submerge it in mineral oil to help it handle it¡¯s rated input for longer? Or should I build a new load? I could also just buy a cantenna at some point.
Chris?
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I wondered the same thing IF I got the MFJ dry dummy load. I don't see any reason why you can't but it might get messy. If I did it, I'm place the dummy load into the container of oil vertically and probably leave the top of the container open. Otherwise, maybe you can unmount the components in the dummy load and use the can lid to remount the components. Might need to find a deeper can if the components are too long. At least the container would be closed and keep the oil from spilling out. Just make sure the container has a "weep hole" in the top to allow the container to breathe and avoid pressure from building up in the can in case the can/oil gets hot.
Bob ¡ª KK5R
On Sunday, November 1, 2020, 12:33:53 AM EDT, Christopher Miller <djmalak2k6@...> wrote:
This is a little off the topic but I have a 100 watt dry load from MFJ. Can I submerge it in mineral oil to help it handle it¡¯s rated input for longer? Or should I build a new load? I could also just buy a cantenna at some point.
Chris?
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My pick,
Easily available on the 'bay for a few bucks! from a few watts to
kilowatts are available.
All you need is a heatsink.
At 01/11/2020, you wrote:
Good info. But when you build
one of those in the image, I suggest that you leave the leads long since
they help dissipate the heat.
Bob ¡ª KK5R
On Saturday, October 31, 2020, 11:08:39 AM EDT, Jack, W8TEE via groups.io
<jjpurdum@...> wrote:
We did a similar DL for the November 2018 QST article which also had a
watt meter built in. By putting the resistor pack in mineral oil, we were
able to run 200W into it for 5 minutes without failure.
Jack, W8TEE
On Saturday, October 31, 2020, 10:43:28 AM EDT, Jerry Gaffke via
groups.io <jgaffke@...> wrote:
Mouser used to sell Xicon 3W metal oxide resistors in small
quantities,
now they have a minimum buy of 100 at $0.10 each.? Darn!?
? 283-100-RC????????
$0.10/100
But they do have a KOA-Speer in single units, haven't gotten any but they
look good:
?
660-MOS3CT631R101J?????????????????????????????????
KOA Speer?? 3W radial metal oxide,? $0.20/1?
$0.15/100
Tayda has a no-name product at $0.06 each with single unit pricing,
? SKU A-2549????? $0.06/1
Those are all 100 ohm, two in parallel from Tayda at $0.12 should be
suitable for use with a uBitx.
20 of the 1000 ohm variant in parallel are 1000/20=50 ohm, good for
20*3=60 Watts continuous.
Also some offerings in metal oxide resistors at 2 Watts instead of 3
Watts.
If you want to spend more than $0.12, here's some proper RF dummy loads
for 100W or more at under $10:
???
???
Will need a good heat sink and thermal paste for those guys.
Search for "RFP Dummy Load" to find other options.
To spend less than $0.12 and have it working today, check out WB9SBD's
baking soda bath:
?
/g/BITX20/message/83207
Jerry, KE7ER
?
--
Jack, W8TEE
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You need a pretty serious heat sink to dissipate 500W though!
I'm planning to try doing a 100W one with a leftover CPU cooler to?get rid of the heat. That should give me a relatively compact dummy load for that power level, though it will require power for the fan.
My pick,
Easily available on the 'bay for a few bucks! from a few watts to
kilowatts are available.
All you need is a heatsink.
At 01/11/2020, you wrote:
Good info. But when you build
one of those in the image, I suggest that you leave the leads long since
they help dissipate the heat.
Bob ¡ª KK5R
On Saturday, October 31, 2020, 11:08:39 AM EDT, Jack, W8TEE via
<jjpurdum=[email protected]> wrote:
We did a similar DL for the November 2018 QST article which also had a
watt meter built in. By putting the resistor pack in mineral oil, we were
able to run 200W into it for 5 minutes without failure.
![Inline image]()
Jack, W8TEE
On Saturday, October 31, 2020, 10:43:28 AM EDT, Jerry Gaffke via
<jgaffke=[email protected]> wrote:
Mouser used to sell Xicon 3W metal oxide resistors in small
quantities,
now they have a minimum buy of 100 at $0.10 each.? Darn!?
? 283-100-RC????????
$0.10/100
But they do have a KOA-Speer in single units, haven't gotten any but they
look good:
?
660-MOS3CT631R101J?????????????????????????????????
KOA Speer?? 3W radial metal oxide,? $0.20/1?
$0.15/100
Tayda has a no-name product at $0.06 each with single unit pricing,
? SKU A-2549????? $0.06/1
Those are all 100 ohm, two in parallel from Tayda at $0.12 should be
suitable for use with a uBitx.
20 of the 1000 ohm variant in parallel are 1000/20=50 ohm, good for
20*3=60 Watts continuous.
Also some offerings in metal oxide resistors at 2 Watts instead of 3
Watts.
If you want to spend more than $0.12, here's some proper RF dummy loads
for 100W or more at under $10:
???
???
Will need a good heat sink and thermal paste for those guys.
Search for "RFP Dummy Load" to find other options.
To spend less than $0.12 and have it working today, check out WB9SBD's
baking soda bath:
?
/g/BITX20/message/83207
Jerry, KE7ER
?
--
Jack, W8TEE
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N8DAH
Bob Lunsford
Raj vu2zap
Shirley Dulcey KE1L