Dummy loads for dummies

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Dummy loads for dummies

Paul C
I made my own dummy load last night from two 100 ohm resistors wired in parallel.  They are rated for 10 watts each and look like little bricks.  I measured the resistance at 51 ohms.  Do you think this is close enough or should I reduce it to 50?

Paul KG5KXG
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Re: Dummy loads for dummies

Kevin - K4VD
​Plenty close enough. Only issue I can think of (besides the normal safety
stuff) is to make sure the resistors are not of the wirewound variety.

Kev K4VD
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Re: Dummy loads for dummies

Elecraft mailing list
In reply to this post by Paul C
>I made my own dummy load last night from two 100 ohm resistors wired in parallel.  They are rated for 10 watts each and look like little bricks.  I measured the resistance at 51 ohms.  Do you think this is close enough or should I reduce it to 50?



>Paul KG5KXG


If your impedance is really 51 ohms, that's an SWR of 1.02. If your antenna had an SWR of 1.02, would you trim it to get to 1.00, fire up your tuner, or just start operating?

However, some of those resistors that look like bricks are really coils (inductors) inside, which produce a higher impedance than the DC resistance. Under RF excitation, that dummy load may be well above 51 ohms impedance. 

73, Ryan AI6DO  
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Re: Dummy loads for dummies

Ken G Kopp
In reply to this post by Paul C
Paul,

Kevin is likely correct.  If those two resistors have a sand-like finish
they're almost certain to be wire wound and therefore will have some
inductance,
which will cause your load to give "uncertain" results.

Your 51 ohm would be OK.  Your ohmmeter isn't -that- accurate, after all.

Elecraft sells a nice load kit that has an additional feature of a
calibrated wattmeter output.

73

Ken Kopp - K0PP



On Dec 27, 2016 7:44 AM, "Paul C" <[hidden email]> wrote:

I made my own dummy load last night from two 100 ohm resistors wired in
parallel.  They are rated for 10 watts each and look like little bricks.  I
measured the resistance at 51 ohms.  Do you think this is close enough or
should I reduce it to 50?

Paul KG5KXG
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Re: Dummy loads for dummies

Elecraft mailing list
In reply to this post by Elecraft mailing list
Yes, and you should test the dummy load at the highest frequency you will be using it.  Even leaded non-inductive resistors will have a reactive component at higher frequencies.
Frankly, I usually test them above the max frequency I intend to use it to not have any concern about error.

Mel,  K6KBE


      From: Ryan Noguchi via Elecraft <[hidden email]>
 To: Paul C <[hidden email]>; "[hidden email]" <[hidden email]>
 Sent: Tuesday, December 27, 2016 8:16 AM
 Subject: Re: [Elecraft] Dummy loads for dummies
   
>I made my own dummy load last night from two 100 ohm resistors wired in parallel.  They are rated for 10 watts each and look like little bricks.  I measured the resistance at 51 ohms.  Do you think this is close enough or should I reduce it to 50?



>Paul KG5KXG


If your impedance is really 51 ohms, that's an SWR of 1.02. If your antenna had an SWR of 1.02, would you trim it to get to 1.00, fire up your tuner, or just start operating?

However, some of those resistors that look like bricks are really coils (inductors) inside, which produce a higher impedance than the DC resistance. Under RF excitation, that dummy load may be well above 51 ohms impedance. 

73, Ryan AI6DO 
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Re: Dummy loads for dummies

Victor Rosenthal 4X6GP
In reply to this post by Paul C
They are undoubtedly wire-wound resistors and will have too much inductance to work well as a dummy load. The resistance is fine. If you have an SWR meter, check it with that. SWR below about 1.5 would mean it is usable. It might be OK on 160 or 80 meters but not on higher bands.

Vic 4X6GP

> On 27 Dec 2016, at 16:43, Paul C <[hidden email]> wrote:
>
> I made my own dummy load last night from two 100 ohm resistors wired in parallel.  They are rated for 10 watts each and look like little bricks.  I measured the resistance at 51 ohms.  Do you think this is close enough or should I reduce it to 50?
>
> Paul KG5KXG
> ______________________________________________________________
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Re: Dummy loads for dummies

John Parker
The good non-inductive resistors are made by Caddock Electronics. Available from some of the catalog dealers.
John WB4UHCK3 #2165

    On Tuesday, December 27, 2016 2:46 PM, Walter Underwood <[hidden email]> wrote:
 

 Ah, yes, bricks. Like these?

https://www.radioshack.com/products/radioshack-100-ohm-10w-10-wirewound-resistor-2-pack# <https://www.radioshack.com/products/radioshack-100-ohm-10w-10-wirewound-resistor-2-pack#>

wunder
K6WRU
Walter Underwood
CM87wj
http://observer.wunderwood.org/ (my blog)

> On Dec 27, 2016, at 11:42 AM, Vic Rosenthal <[hidden email]> wrote:
>
> They are undoubtedly wire-wound resistors and will have too much inductance to work well as a dummy load. The resistance is fine. If you have an SWR meter, check it with that. SWR below about 1.5 would mean it is usable. It might be OK on 160 or 80 meters but not on higher bands.
>
> Vic 4X6GP
>
>> On 27 Dec 2016, at 16:43, Paul C <[hidden email]> wrote:
>>
>> I made my own dummy load last night from two 100 ohm resistors wired in parallel.  They are rated for 10 watts each and look like little bricks.  I measured the resistance at 51 ohms.  Do you think this is close enough or should I reduce it to 50?
>>
>> Paul KG5KXG
>> ______________________________________________________________
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Re: Dummy loads for dummies

Paul C
In reply to this post by Victor Rosenthal 4X6GP
Ok, I won't be using these resistors after all.  Thanks for setting me straight.

It seems tuff to get going in QRP.  I thought I'd roll my own when possible.  I am trying to keep things simple and economical, the QRP spirit.

Here's another naive idea of mine:  I'm planning to use ladder line too.  Now I'm waiting for the other shoe to drop, when I realize coax will be my only practical choice.

Paul KG5KXG

-----Original Message-----
From: "Walter Underwood" <[hidden email]>
Sent: ‎12/‎27/‎2016 1:45 PM
To: "[hidden email]" <[hidden email]>
Subject: Re: [Elecraft] Dummy loads for dummies

Ah, yes, bricks. Like these?

https://www.radioshack.com/products/radioshack-100-ohm-10w-10-wirewound-resistor-2-pack# <https://www.radioshack.com/products/radioshack-100-ohm-10w-10-wirewound-resistor-2-pack#>

wunder
K6WRU
Walter Underwood
CM87wj
http://observer.wunderwood.org/ (my blog)

> On Dec 27, 2016, at 11:42 AM, Vic Rosenthal <[hidden email]> wrote:
>
> They are undoubtedly wire-wound resistors and will have too much inductance to work well as a dummy load. The resistance is fine. If you have an SWR meter, check it with that. SWR below about 1.5 would mean it is usable. It might be OK on 160 or 80 meters but not on higher bands.
>
> Vic 4X6GP
>
>> On 27 Dec 2016, at 16:43, Paul C <[hidden email]> wrote:
>>
>> I made my own dummy load last night from two 100 ohm resistors wired in parallel.  They are rated for 10 watts each and look like little bricks.  I measured the resistance at 51 ohms.  Do you think this is close enough or should I reduce it to 50?
>>
>> Paul KG5KXG
>> ______________________________________________________________
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Re: Dummy loads for dummies

Elecraft mailing list
In reply to this post by Victor Rosenthal 4X6GP
Or these, they are good to VHF range. 
non inductive resistor Passive Components | Mouser
But if you want something that is good to microwave, then use 4 each 200 ohms 1206 chip resistors around a panel mount female BNC connector.  Works slick.
Mel, K6KBE

 
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non inductive resistor Passive Components | Mouser
 non inductive resistor Passive Components are available at Mouser Electronics. Mouser offers inventory, pricing,...  |   |

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      From: Walter Underwood <[hidden email]>
 To: "[hidden email]" <[hidden email]>
 Sent: Tuesday, December 27, 2016 11:44 AM
 Subject: Re: [Elecraft] Dummy loads for dummies
 
Ah, yes, bricks. Like these?

https://www.radioshack.com/products/radioshack-100-ohm-10w-10-wirewound-resistor-2-pack# <https://www.radioshack.com/products/radioshack-100-ohm-10w-10-wirewound-resistor-2-pack#>

wunder
K6WRU
Walter Underwood
CM87wj
http://observer.wunderwood.org/ (my blog)

> On Dec 27, 2016, at 11:42 AM, Vic Rosenthal <[hidden email]> wrote:
>
> They are undoubtedly wire-wound resistors and will have too much inductance to work well as a dummy load. The resistance is fine. If you have an SWR meter, check it with that. SWR below about 1.5 would mean it is usable. It might be OK on 160 or 80 meters but not on higher bands.
>
> Vic 4X6GP
>
>> On 27 Dec 2016, at 16:43, Paul C <[hidden email]> wrote:
>>
>> I made my own dummy load last night from two 100 ohm resistors wired in parallel.  They are rated for 10 watts each and look like little bricks.  I measured the resistance at 51 ohms.  Do you think this is close enough or should I reduce it to 50?
>>
>> Paul KG5KXG
>> ______________________________________________________________
>> Elecraft mailing list
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>>
>> This list hosted by: http://www.qsl.net
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Re: Dummy loads for dummies

Kevin - K4VD
In reply to this post by Paul C
​Well now I don't think anyone said the wirewounds wouldn't work just that
you'd need to check them out. Give it a shot and see if the SWR is as
expected. I've used cheap carbon comp resistors in the past​. Heck, a light
 bulb (incandescent) probably wouldn't do a bad job.

As for your other idea, using ladder line, it's about the best choice for
QRP I think as it generally is lower loss. I use 600 ohm ladder line but I
don't know if that's any better or worse electrically than 450 ohm window
line or even 300 ohm tv line.

Kev
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Re: Dummy loads for dummies

Victor Rosenthal 4X6GP
In reply to this post by Paul C
I'm using ladder line to feed a 20m dipole on all bands from 40-10m
(actually, it even works on 6m). Using a dipole shorter than 1/2
wavelength can be tricky, but it should work pretty well on the design
frequency and higher. You will need to use a balanced antenna tuner, or
an unbalanced tuner plus a balun.

There's an article about how I did this in this newsletter:
<http://www.cwops.org/newsletter/2016/08scopy16aug.pdf>

73,
Vic, 4X6GP
Rehovot, Israel
Formerly K2VCO
http://www.qsl.net/k2vco/

On 27 Dec 2016 22:22, Paul C wrote:

> Ok, I won't be using these resistors after all.  Thanks for setting
> me straight.
>
> It seems tuff to get going in QRP.  I thought I'd roll my own when
> possible.  I am trying to keep things simple and economical, the QRP
> spirit.
>
> Here's another naive idea of mine:  I'm planning to use ladder line
> too.  Now I'm waiting for the other shoe to drop, when I realize coax
> will be my only practical choice.
>
> Paul KG5KXG
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Re: Dummy loads for dummies

Bill K9YEQ
In reply to this post by Elecraft mailing list
Easiest solution, buy the Elecraft DL1 20 watt dummy load kit.  The guess work is removed.  And it is only $25.95 for the kit.  Fun to build simple to use.  Even has an RF detector built on.

73,
Bill
K9YEQ

-----Original Message-----
From: Elecraft [mailto:[hidden email]] On Behalf Of Walter Underwood
Sent: Tuesday, December 27, 2016 12:42 PM
To: [hidden email]
Subject: Re: [Elecraft] Dummy loads for dummies

If you want a dummy load kit for about as much as you would pay for the box, I highly recommend the Oak Hills Research RFL-100 kit for $40.

http://www.ohr.com/rfl100.htm <http://www.ohr.com/rfl100.htm>

I used their “BNC in a UHF connector hole” kit to make my dummy load more convenient in my all-BNC shack.

http://www.ohr.com/parts.htm <http://www.ohr.com/parts.htm>

wunder
K6WRU
Walter Underwood
CM87wj
http://observer.wunderwood.org/ (my blog)

> On Dec 27, 2016, at 9:41 AM, Mel Farrer via Elecraft <[hidden email]> wrote:
>
> Yes, and you should test the dummy load at the highest frequency you will be using it.  Even leaded non-inductive resistors will have a reactive component at higher frequencies.
> Frankly, I usually test them above the max frequency I intend to use it to not have any concern about error.
>
> Mel,  K6KBE
>
>
>      From: Ryan Noguchi via Elecraft <[hidden email]>
> To: Paul C <[hidden email]>; "[hidden email]"
> <[hidden email]>
> Sent: Tuesday, December 27, 2016 8:16 AM
> Subject: Re: [Elecraft] Dummy loads for dummies
>
>> I made my own dummy load last night from two 100 ohm resistors wired in parallel.  They are rated for 10 watts each and look like little bricks.  I measured the resistance at 51 ohms.  Do you think this is close enough or should I reduce it to 50?
>
>
>
>> Paul KG5KXG
>
>
> If your impedance is really 51 ohms, that's an SWR of 1.02. If your antenna had an SWR of 1.02, would you trim it to get to 1.00, fire up your tuner, or just start operating?
>
> However, some of those resistors that look like bricks are really coils (inductors) inside, which produce a higher impedance than the DC resistance. Under RF excitation, that dummy load may be well above 51 ohms impedance.
>
> 73, Ryan AI6DO
> ______________________________________________________________
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>
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Re: Dummy loads for dummies

Don Wilhelm
In reply to this post by Paul C
Paul,

For the ladderline vs. coax question, you might want to take a look at
the article I wrote for QRP Quarterly some years back.  If so, go to my
website www.w3fpr.com and look at the Antenna, Transmission Lines and
Tuners article.  You can also find that article at
http://www.dxzone.com/dx19232/antennas-and-transmission-lines-myths.html 
- I am pleased that DXzone has chosen to preserve it.

73,
Don W3FPR

On 12/27/2016 3:22 PM, Paul C wrote:
> Ok, I won't be using these resistors after all.  Thanks for setting me straight.
>
> It seems tuff to get going in QRP.  I thought I'd roll my own when possible.  I am trying to keep things simple and economical, the QRP spirit.
>
> Here's another naive idea of mine:  I'm planning to use ladder line too.  Now I'm waiting for the other shoe to drop, when I realize coax will be my only practical choice.
>
> Paul KG5KXG
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Re: Dummy loads for dummies

Don Wilhelm
In reply to this post by John Parker
I use those Caddock Thick Film Power resistors to make my own dummy
loads.  They make flat dummy loads up to at least 200MHz with normal
lead dress, and with care they can be flat up to 500MHz.
I have found is that the 50 ohm resistors are non-reactive, but other
values may be capacitive.

They MUST be used on a heatsink adequate for their power rating or else
their power rating is quite low.  They will zap in an instant if their
power rating (device and the heatsink) are exceeded, so put them on a
heatsink that is sufficient for the power rating.

73,
Don W3FPR

On 12/27/2016 3:21 PM, John Parker wrote:
> The good non-inductive resistors are made by Caddock Electronics. Available from some of the catalog dealers.
> John WB4UHCK3 #2165
>
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Re: Dummy loads for dummies

Wes Stewart-2
In reply to this post by Paul C
Paul,

You've got a lot of hand wringing comments about how those are probably wire
wound resistors.  They probably are but in practice it might not matter.  It all
depends on what exactly you are trying to accomplish.   You don't say what your
usage is or how much power your TX is putting out.

Wes  N7WS

  On 12/27/2016 7:43 AM, Paul C wrote:
> I made my own dummy load last night from two 100 ohm resistors wired in parallel.  They are rated for 10 watts each and look like little bricks.  I measured the resistance at 51 ohms.  Do you think this is close enough or should I reduce it to 50?
>
> Paul KG5KXG

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Re: Dummy loads for dummies

Alan Bloom
I once made a dummy load with a 50W, 50-ohm wire-wound resistor.  The
inductance was tuned out with a variable capacitor in series.  As I
recall it worked reasonably well on 160 and 80 meters, but the bandwidth
was too narrow to be useful on the high bands.

Alan N1AL


On 12/27/2016 02:31 PM, Wes Stewart wrote:

> Paul,
>
> You've got a lot of hand wringing comments about how those are probably
> wire wound resistors.  They probably are but in practice it might not
> matter.  It all depends on what exactly you are trying to accomplish.
> You don't say what your usage is or how much power your TX is putting out.
>
> Wes  N7WS
>
>  On 12/27/2016 7:43 AM, Paul C wrote:
>> I made my own dummy load last night from two 100 ohm resistors wired
>> in parallel.  They are rated for 10 watts each and look like little
>> bricks.  I measured the resistance at 51 ohms.  Do you think this is
>> close enough or should I reduce it to 50?
>>
>> Paul KG5KXG
>
> ______________________________________________________________
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Re: Dummy loads for dummies

Don Wilhelm
In reply to this post by Wes Stewart-2
Wes,

What you say is true, and how much it matters in practice will vary
depending on just how much inductance is present  in those wirewound
resistors. how much it matters depends of frequency.  The higher the
frequency, the more it matters - and that is independent of power.

The load in question is for initial testing of a KX1 at 40 and 20
meters.  If only an indication of some power output capability is
required, then that load may be sufficient, but in this case, the owner
wants to know if his KX1 is operating up to specifications, and a
non-inductive dummy load is required for that purpose, in addition a
means of accurately measuring the power output at a 3 to 4 watt level is
also an essential tool.  An RF probe applied across the dummy load may
provide that indication at 4 watts or less (along with a little math),
but if the power is much greater than that, it will zap the most
commonly used diode in the RF Probe (a 1N34).

So you are correct, if simply providing a load to a transmitter, the
wirewound resistors may be OK, but if they are being used as a
measurement tool, the results will be incorrect if only the DC
resistance is considered.  The real result of any measurements done with
reactive components can only be had by also considering the complex
impedance of the load.  Measurements with an RF Probe and a DVM will not
reveal that complex impedance that must be entered into the equation.

73,
Don W3FPR

On 12/27/2016 5:31 PM, Wes Stewart wrote:
> Paul,
>
> You've got a lot of hand wringing comments about how those are probably
> wire wound resistors.  They probably are but in practice it might not
> matter.  It all depends on what exactly you are trying to accomplish.
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Re: Dummy loads for dummies

Elecraft mailing list
In reply to this post by Paul C
One thing I might also add in.  I use the Film TO-220 style non-inductive resistors with a heat sink in the 200 ohm 1% configuration to test 4:1 baluns at 100 watt level to confirm non saturation on the small QRP baluns I make.
Mel, K6KBE


      From: Ron D'Eau Claire <[hidden email]>
 To: 'Paul C' <[hidden email]>; [hidden email]
 Sent: Tuesday, December 27, 2016 3:23 PM
 Subject: Re: [Elecraft] Dummy loads for dummies
   
For parts, digikey.com and mouser.com are good friends. No minimum order, great prices and huge selection.

You've gotten several suggestions for a good dummy load. And I concur with the others, those wire-wound resistors might be 50 ohms but their reactance may almost anything and dependent upon frequency. One of the original "Elecrafter Field Testers" and "F.O.W." - friend of Wayne (Burdick) - was Tom Hammond, N0SS, no sadly an S.K. But his web site has been maintained and it contains a great low-cost dummy load design:

http://www.mmccs.com/mmarc/n0ss/dl_30w_hf-uhf.pdf

You might enjoy looking around the web site for more KX1 info and QRP info in general:

http://www.mmccs.com/mmarc/n0ss/

Coaxial cable is every much as low loss as open wire line when the SWR is not too high. The difference in applying them is that the inherently higher-impedance of ladder line makes it much easier to keep the SWR on the line low enough to avoid excessive loss. For example, a hunk of wire between 50 and 100 feet long strung up in the air and fed at its center will show an impedance of about 4,000 ohms at the frequency at which it is 1/2 wavelength long and perhaps as low as 40 ohms on 80 or 160 meters. With open wire line at about 400 ohms impedance, you will find an SWR of up to 10:1 on the feed line, generally much less. With 50 ohm coax, the SWR will range as high as 80:1 or more.

Have fun. At my shack, simple and cheap is great fun!

73, Ron AC7AC



-----Original Message-----
From: Elecraft [mailto:[hidden email]] On Behalf Of Paul C
Sent: Tuesday, December 27, 2016 12:23 PM
To: Walter Underwood; [hidden email]
Subject: Re: [Elecraft] Dummy loads for dummies

Ok, I won't be using these resistors after all.  Thanks for setting me straight.

It seems tuff to get going in QRP.  I thought I'd roll my own when possible.  I am trying to keep things simple and economical, the QRP spirit.

Here's another naive idea of mine:  I'm planning to use ladder line too.  Now I'm waiting for the other shoe to drop, when I realize coax will be my only practical choice.

Paul KG5KXG

-----Original Message-----
From: "Walter Underwood" <[hidden email]>
Sent: ‎12/‎27/‎2016 1:45 PM
To: "[hidden email]" <[hidden email]>
Subject: Re: [Elecraft] Dummy loads for dummies

Ah, yes, bricks. Like these?

https://www.radioshack.com/products/radioshack-100-ohm-10w-10-wirewound-resistor-2-pack# <https://www.radioshack.com/products/radioshack-100-ohm-10w-10-wirewound-resistor-2-pack#>

wunder
K6WRU
Walter Underwood
CM87wj
http://observer.wunderwood.org/ (my blog)

> On Dec 27, 2016, at 11:42 AM, Vic Rosenthal <[hidden email]> wrote:
>
> They are undoubtedly wire-wound resistors and will have too much inductance to work well as a dummy load. The resistance is fine. If you have an SWR meter, check it with that. SWR below about 1.5 would mean it is usable. It might be OK on 160 or 80 meters but not on higher bands.
>
> Vic 4X6GP
>
>> On 27 Dec 2016, at 16:43, Paul C <[hidden email]> wrote:
>>
>> I made my own dummy load last night from two 100 ohm resistors wired in parallel.  They are rated for 10 watts each and look like little bricks.  I measured the resistance at 51 ohms.  Do you think this is close enough or should I reduce it to 50?
>>
>> Paul KG5KXG
>> ______________________________________________________________
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Re: Dummy loads for dummies

Clay Autery
Makes me curious about designing with these TO-220 resistors in the 1000
Ohm size of appropriate power rating...  Parallel 20 of them like folks
do on the axials that they put in the can type dummy loads with oil.

Options:

1) 20 in parallel on a finned copper or bare aluminum sink of sufficient
size and then entire assembly in a oil wetted container.
2) Same, but only the finned side of the finned/pinned heat exchanger in
a coolant bath.

I'd like to have a rugged, high power, key down load built from easily
obtainable and replaceable parts.

______________________
Clay Autery, KY5G
MONTAC Enterprises
(318) 518-1389

On 12/27/2016 5:52 PM, Mel Farrer via Elecraft wrote:
> One thing I might also add in.  I use the Film TO-220 style non-inductive resistors with a heat sink in the 200 ohm 1% configuration to test 4:1 baluns at 100 watt level to confirm non saturation on the small QRP baluns I make.
> Mel, K6KBE
>
>

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Re: Dummy loads for dummies

Elecraft mailing list
I have seen on ebay (I believe Henry Radio is the vendor) some pretty high wattage loads
(I believe at one time they sold a set of 4 200ohm ones to mount to a big heat sink.)

If I were going to run a tube amp again I'd be tempted to make up a high wattage dummy load for it.

 

      From: Clay Autery <[hidden email]>
 To: [hidden email]
 Sent: Tuesday, December 27, 2016 7:16 PM
 Subject: Re: [Elecraft] Dummy loads for dummies
   
Makes me curious about designing with these TO-220 resistors in the 1000
Ohm size of appropriate power rating...  Parallel 20 of them like folks
do on the axials that they put in the can type dummy loads with oil.

Options:

1) 20 in parallel on a finned copper or bare aluminum sink of sufficient
size and then entire assembly in a oil wetted container.
2) Same, but only the finned side of the finned/pinned heat exchanger in
a coolant bath.

I'd like to have a rugged, high power, key down load built from easily
obtainable and replaceable parts.

______________________
Clay Autery, KY5G
MONTAC Enterprises
(318) 518-1389

On 12/27/2016 5:52 PM, Mel Farrer via Elecraft wrote:
> One thing I might also add in.  I use the Film TO-220 style non-inductive resistors with a heat sink in the 200 ohm 1% configuration to test 4:1 baluns at 100 watt level to confirm non saturation on the small QRP baluns I make.
> Mel, K6KBE
>
>

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