You can eliminate a lot of that weight by using a switching power supply.
Fern VE7GZ
----- Original Message -----
From: "Roger (sub1)" <sub1@rogerhalstead.com>
To: <amps@contesting.com>
Sent: Tuesday, April 05, 2011 9:37 PM
Subject: Re: [Amps] Alpha vs Henry
> On 4/5/2011 7:08 PM, Roger (sub1) wrote:
>> On 4/4/2011 10:44 PM, Bill, W6WRT wrote:
>>> ORIGINAL MESSAGE:
>>>
>>> On Mon, 04 Apr 2011 15:17:23 -0400, "Roger (sub1)"
>>> <sub1@rogerhalstead.com> wrote:
>>>
>>>> , a true 1500 watt
>>>> amp needs to be capable of nearly twice that to hold together.
>>> REPLY:
>>>
>>> That doesn't make sense. If it can't "hold together" at 1500 watts, it
>>> is not a "true" 1500 watt amp.
>
> How about we put some figures on this that are pretty much applicable to
> the real world and I hope I can keep the numbers straight without making
> a mistake. <:-)) That and there are others on here who are much better
> than I at making these calculations for real amps.
>
> SSB is figured at 20% duty cycle and CW at 40% for RF exposure. These
> figures should be close enough for design work. This is neglecting any
> off time. The typical on, off time is some times calculated at 10 minute
> transmissions and receiving 10 minutes which in a 30 minute cycle would
> be 66.7% on time. Of course in that scenario the other guy is only
> running a 33% duty cycle.
>
> The following is an over simplification as the transformers calculated
> would likely be insufficient due to cool down time and heat retention.
> it also makes the overly optimistic assumption that efficiency will be
> 60 % on all bands. These sizes should be considered absolute minimums.
> In real life or IRL as the flight simmers say, I'd add at least another
> 20% to the transformer size just to be safe. Actually I'd add quite a
> bit more for comfort.
>
> So if we are running 1500 watts output at 60% efficient then the input
> needs to be 1500/0.60 or 2500 watts pep input, but it's only 20% duty
> cycle. or 500 watts. Neglecting the inefficencies in the power supply we
> can build a legal limit amp with an HV transformer of only 1/2 KVA.
> Switch to CW with 40% duty cycle and we suddenly need a 1 KVA
> transformer. IOW one that weighs twice as much. But what if we want to
> run digital or any other mode considered 100% duty cycle. Then we need
> a transformer of at least 2.5 KVA, or 5 times the size of the one we
> used for SSB only. An amp capable of 1500 out at 100% is *Heavy*!
>
>
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