It's not who's right, it's who put in components such as the PS that are
capable of running at tilt all day long. With tube amps it's normal for
one that will run the legal limit all day long to be heavier, larger,
more expensive, and capable of running substantially more than the legal
limit, than many, or most "legal limit" amps that are not computer
controlled.
With the computer controlling the power they can build an amp capable of
running the legal limit all day long, yet not run far more than the
legal limit on SSB. Of course you pay for that extra capability.
I can think of two reasons for the above. To build a true legal limit
tube amp with no time limit, the amp will likely be capable of 2 to 2.5
KW PEP (or more) and the FCC might frown on that. The other is
"cheap"! They can claim it's a legal limit amp, which it is for SSB,
but derated in other modes. They can run a lower plate voltage which
also lets them use a smaller and lighter transformer. IOW, the time
limit comes because of the components in the PS and is set by how hot
they are willing to run the transformer.
Of course there is the heat output as well. Ignoring other sources, at
60% efficient (give or take) you are going to run at least 2500 W input
for 1000 watts of heat just from the plate efficiency. AB1 will give
you even more. At 25% class A makes one whale of a space heater!
Some companies sell amps that have a higher output than the tubes are
rated to put out, or they rate them at an output power that will
drastically shorten the life of the tubes, not to mention as to what
running them that way does to the IM. I can run the legal limit all day
long with good IM figures as reported on the air and the transformer
only gets warm. With lots of audio processing with my long winded
transmissions, it will kick into high blower which I hardly notice in
the shop, but you better be wearing a headset in this small den. Since
I have operated here in the den most of the time over the past few
years, I have used the amp only a couple of time because of the noise,
but mostly because of the heat. This room gets uncomfortably warm
because of the computers. With the amp, (in the summer) it gets
downright miserable, so as soon as I get the shop reorganized the amp
goes back out! The shop is one air conditioned room the size of my
entire house, so a KW of heat isn't even noticed.
When the THP SS amp, it was quiet, instant on, or nearly so, and instant
band change. I often wish I'd have kept it, although I do like the big
amp (in the shop)
73
Roger (K8RI)
On 4/24/2015 7:50 PM, Kevin Stover wrote:
On Fri, 24 Apr 2015 18:45:16 -0500
Kevin Stover <kevin.stover@mediacombb.net> wrote:
I forgot to add that Ameritron also derates the AL-1500 to no more than half an hour at
full power. Alpha is famous for the "brick on the key". Who's right?
I'll take your word for it.
I don't know of any solid state 1KW amp that doesn't derate the power out for
constant key down modes like RTTY, AM, and FM. I believe the KPA 500 is derated
to no more than 15 minutes key down at full power. Maybe the 1306 wil do 600W
all day long.
On Fri, 24 Apr 2015 16:22:08 -0700
Bill Turner <dezrat@outlook.com> wrote:
REPLY:
Did Ameritron ever state the duty cycle limit for the 1306? I phoned
them on the 1300 and they told me 600 watts for RTTY or other full
carrier modes.
73, Bill W6WRT
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R. Kevin Stover
AC0H
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