On Mon, 8 Sep 1997 08:27:35 +0000 w8jitom@postoffice.worldnet.att.net
writes:
>> From: km1h@juno.com (km1h @ juno.com)
>> Subject: Re: [AMPS] SB-220 problem
To: <amps@contesting.com>
>> Date: Sun, 7 Sep 97 18:11:07 +0000
>
>>
>> On Sun, 7 Sep 1997 11:30:09 +0000
>w8jitom@postoffice.worldnet.att.net
>> writes:
>
>> >The SB-220 DESIGN specs are as I indicated. Look them up.
>>
>> Do your "DESIGN" specs differ from the published specs in the
>manual?
>
>Not so far as I know or Heathkit knew.
>
>> I'll stick with my earlier statement thank you. BTW, try pages 79
>and
>> 80 in the manual and then tell me how you come up with a 600W limit.
>You
>> must be using Rich's math.
>
>Let's see. The maximum key down input power rating is 1000 watts dc
>plate input on CW. The efficiency on a good day with a good 220 is
>about 60 percent. I suspect that's about 600 watts rated CW output,
>unless my math is flawed.
>
>The SB-220 was designed to operate at 1000 watts dc plate input
>power on CW, and 1000 watts meter ***indicated*** plate input
>power on SSB.
Yep, but you have a way with words that bears watching. That "indicated"
reading on SSB was really 2000W PEP input power and is so stated in the
Heath Specifications. That was perfectly legal at the time. Using the
same math as you, that then translates to 1200W or better PEP Output.
In the CW position a SB-220 will run up to 800-900W out with 100W of
drive so there is some reserve overhead.
In order to provide and reliably sustain 1200W the PS and other
components were designed and rated for that power. The manual also states
that the current draw on a 240VAC line is a maximum of 10A. That is not
the ratings of a 600W amp which is what started this discussion since you
claimed the SB-220 was only a 600W capable amp.
> That was the law at the time the PA was designed,
>there was never any hint the power rating would be nearly tripled
>later on.
No, but many a ham ran CW in the SSB position then. The only law that
changed was the FCC's not the actual capability of the amp. Speech
processors were also popular which upped the requirements of the PS to CW
duty cycle. But perhaps I am pushing the limits here a bit. After all,
you were still in high school when many of these fine amps debuted.
>
>The old two kW PA's are nothing near as heavy duty as the modern 1500
>watt PA's, because the rating system is very different today.
Yeah, a few manufacturers cheat a lot more with power ratings today and a
lot more hams cheat also. I wonder how many big amps would be sold today
if the FCC mandated circuitry that would automatically fold back power
past 1500W in any mode?
A 2KW PA of yesteryear is the 1200-1400W PEP PA of today, not 600W. Most
2 x 3-500Z amps from the past are still capable of many, many years of CW
and SSB use at that level without fear of a meltdown. I would think
that even you would agree that there is no meaningful difference at the
receive end between 1200-1400W and 1500W.
> I'm sorry if you disagree with that,
Your sincerity certainly shows.
> but it's true so far as I know from
>looking at the FCC rules, equipment manuals, and engineering
>specs.
>
>73, Tom W8JI
73....Carl KM1H
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