Re: Parallel Resistance calculator


John T. Fitzer
 

 

 

From: main@4SQRP.groups.io [mailto:main@4SQRP.groups.io] On Behalf Of John T. Fitzer
Sent: Thursday, June 21, 2018 8:19 AM
To: main@4SQRP.groups.io; kennick@...
Subject: Re: [4SQRP] Parallel Resistance calculator

 

Regarding the dummy load idea, Back in the days when I was running QRO (100) watts, I made a dummy load by immersing 20 1Kohm 2 watt carbon resistors in a quart of mineral oil with a SO239 mounted to the top of the can lid. From a practical point of view, and without getting too deep into thermodynamics it is safe to assume that as a rule of thumb, any resistor immersed in oil will increase its dissipation capabilities by a factor of 4. So theoretically my red neck dummy load should be able to handle 160 watts. I never tested it at that power level, but as I remember it never even got warm at 100 watts. Keep in mind I never held the key down for more the a minute or so. I was more concerned about killing the 6146’s.  

 

From: main@4SQRP.groups.io [mailto:main@4SQRP.groups.io] On Behalf Of Howard Weinstein
Sent: Wednesday, June 20, 2018 8:23 PM
To: main@4SQRP.groups.io; kennick@...
Subject: Re: [4SQRP] Parallel Resistance calculator

 

Or you could immerse them in oil and make a unique dummy load

"Quis custodiet ipsos custodes?”


On Jun 20, 2018, at 20:45, Nick Kennedy <kennnick@...> wrote:

This reminds me of an article in QST in July 1963 called "Euclid and a quart of resistors". It showed how to take a quantity of resistors of a single value (say you have a quart of 47 ohm, 1% resistors ...) and combine them to produce any value, exactly.

 

I guess I'm regressing to my youth because I looked up that 55 year old article and ran though a couple examples to see that it worked. I don't think it really has much practical value - it's just an interesting demonstration of a technique.

 

73-

 

Nick, WA5BDU

 

On Wed, Jun 20, 2018 at 2:45 PM WA0ITP <wa0itp@...> wrote:

A while back someone  posted, on some list, a link to a calculator that provided abt 15 or so parallel resistor combination which matched a desired value that was entered into the calculator.  Matching parallel values were tabulated as were error deviations in percent. Alas I lost the email with the link.

Google is not my friend on this.  Did anyone here see and save that email/link?  Thanks for checking, appreciate it.

-- 
72 WAØITP
I love this radio stuff.
www.wa0itp.com
www.4sqrp.com

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