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Re: [CQ-Contest] Power consumption question

To: "'Tony Rogozinski'" <trogo@telegraphy.com>,<cq-contest@contesting.com>
Subject: Re: [CQ-Contest] Power consumption question
From: "Joe Subich, W4TV" <w4tv@subich.com>
Date: Mon, 17 Dec 2007 13:30:24 -0500
List-post: <mailto:cq-contest@contesting.com>

It is not the average power that will get you it is the peak 
power.  The Alphas have capacitor input filters in the power 
supply which means that although the average current draw may 
be low enough the peak current will be tree or four times the 

Start with an Alpha that will probably do 2500 W output.  I 
don't know of many that won't - even the old "three tube" 76.
With filament power and transformer efficiency, you will be 
lucky to see 50% overall efficiency from AC input to RF out 
so you can figure 5 KW of input power per amplifier - at 210 
volts (optimistic for your line) your average current at 
peak output will be right around 24 amps (210 * 24 = 5.04 KVA). 
The peak current will depend on the conduction angle of the 
power supply which will be based on the transformer impedance, 
HV current draw, amount of filter capacitance and type of 
rectifier (full wave bridge or voltage doubler) but use a 
factor of four for safety.  Now you are looking at 100 A 
peak currents in the supply.  Can the stabilizer handle that 
for one amplifier?  What about double that if both amplifiers 
are transmitting at the same time?  

You might be far better off setting the transformer for 200 V 
(assuming the standard 200/220/240 transformer is used) and 
adding dropping resistors to the filament circuit to bring 
the filament voltage down if necessary. 


   ... Joe, W4TV 

> -----Original Message-----
> From: cq-contest-bounces@contesting.com 
> [mailto:cq-contest-bounces@contesting.com] On Behalf Of Tony 
> Rogozinski
> Sent: Monday, December 17, 2007 10:39 AM
> To: cq-contest@contesting.com
> Subject: [CQ-Contest] Power consumption question
> The 220 Volt lines here in Bogota only supply about 207/208 
> volts which
> is not sufficient to power up an Alpha amp.  (question asked 
> previously
> how to correct this problem)  I have found  a 5000 watt 
> Voltage Converter
> Stabilizer at a good price and am wondering if this unit would be 
> sufficiently
> large for two Alpha's  at the same time.  Seems like each 
> would draw maybe
> 7-9 amps if my math is correct and this unit would handle at 
> least 20 amps?
> It's been about 30 years since I studied electronics and have 
> forgotten 
> nearly
> everything I ever knew!
> Any response appreciated.
>                        Tony Rogozinski
>        Amateur Radio W4OI - W4AMR - HK1AR
>             LICENSED FOR OVER 50 YEARS
>          EX-N7BG, K5LMJ, K4KES, WA6BOU,
>        W6JPC W7HZF, F7BK, VP5AR, VQ9AR,
>           OJ0/N7BG, CN2BG, 5V7BG, TY5AR
>           9G5AR, TU/N7BG, ZC4BG, HK3KAV
>                   HK0/HK1AR, et al............
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