[NJARC] Voltage Drop, Ham Radio...

[John Ruccolo]

Hi Scott,

OK, I *think* I have this right. Any others feel free to chime in.

You've got 150V and you want to drop it to 120V to feed a load that draws 25 mils. (.025 ampere).

So the voltage drop is 30V

Ohm's Law: I=E/R

R (the dropping resistor) = E/I

R = 30/.025 = 1200 ohms (great -- that's a standard value!)

Now, your next question: how big should R be?

P = I * E

P = .025 * 30 = .75 watt

So, a 1-watt resistor would be OK, but just to be safe, good practice would be to use a 2-watt resistor


Regards,

John


--- On Mon, 7/27/09, Scott Roberts <ng19delta at yahoo.com> wrote:

> From: Scott Roberts <ng19delta at yahoo.com>
> Subject: [NJARC] Voltage Drop, Ham Radio...
> To: "NJARC Radio Club" <njarc at mailman.qth.net>
> Date: Monday, July 27, 2009, 1:10 PM
> Just remember 
> Reply = Poster
> Reply All = Everyone
> 
> _________________________________________________________
> 
> Well, I am very close to getting my Hallicrafters HT-37 on
> the air. Great Thanks to John Ruccolo for getting together
> with me after the swapmeet Saturday at InfoAge(Great
> Swapmeet!) and going through the HT-37. We got it to a
> decent point where it was showing great signs of life,
> especially after some tube replacement(Thanks to Al Klase
> for locating a few tubes for us)
> 
> It now looks like I should be on HF this week.
> 
> Voltage Dropping Question- In order to use the HF sets, I
> need to get my vacuum tube Dow-Key powered. It takes
> 90-120VDC & 6VDC. I would like to pull the power from
> the receiver- it has a 150VDC available, and so i need to
> know how to drop it to 110-120 or so... I know I can add a
> couple power resistors, but not sure how much. Can anyone
> give me any ideas? 
> 
> I am still lousy at these calculations still... On of these
> days!
> 
> Thanks!
> Scott
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