On 5/23/2015 9:37 PM, Charles Henry wrote:
I wanted a full size rig and the FT5000MP is all of that. It takes
about the same 60 watts in class A to get the legal limit out of my
DX-2sp. 75 watts is max for class A at which the amp draws the least
power. In class A it dissipates the most power with zero signal.
There is a specific sequence for setting up the audio and drive for the
5000MP just as there is for Icom and Kenwood rigs. I don't know about
the 990 Kenwood, or the new, $15,000 Icom, but even on class AB1 the
Yaesu is much cleaner than older rigs with little overhead. I would
assume the Kenwood and new Icom benefit from backing off on the drive
and a proper set up with little customization
As to the K3, I didn't see any complimentary comments relating to the
quality of the transmitted signal. To the contrary, I did see complaints.
Unless you can listen to an A/B comparison between the two rigs "on a
quiet band", most comparisons would mean little. I can state the Yaesu
is rated with a cleaner signal. Of course, driving the amp with only
60-70 watts AB1 gives a pretty clean signal as well as it's well away
from the compression knee and there are no leading waveform spikes to
drive the amp into saturation.
Jim had it correct with those rigs running 100 watts when capable of
200. They take advantage of that headroom.
It seems as if we are passing on the old habits from generations back of
squeezing every db possible out of of a circuit/final. Tune the final
properly whether a Triode, or Tetrode and don't drive SS amps anywhere
near that compression knee. Yes the Orange/Red button (the one on mine
is decidedly orange) makes a difference on an analyzer. Does it make a
difference to adjacent stations on the bands? I don' know as I've never
received an on-the-air complaint. I have received surprised sounding,
"Did you say you are running a Tetrode final?" No doubt from tetrodes
being driven by rigs with a decided leading edge spike, particularly at
reduced power.
The DX-2sp is capable of running 2500 PEP, so it's loafing along at 1500
with substantial compression, or even on digital although I've been told
that will kick the final into high blower. We've reached that time of
year where it's time to send the big amp back to the shop. That amp can
make this tiny room all warm and toasty. High blower is downright
noisy, yet in that 30 X 40 foot shop, it's hardly noticeable.
To get that 2X headroom in SS is about the cost of another Chinese
8877/3CX1500A7
Doesn't it make more sense to gain the headroom instead of having to
resort to predistortion (either adaptive, or fixed)
Headroom is simple as is negative feedback. Predistortion is at least
one more thing to go wrong.
To paraphrase a rather infamous author, "never let a good headroom go to
waste!" Which is why we'll probably never see it used except in
computer controlled amps.
73
Roger (K8RI)
I see extoling comments re K3 clean xmitter. What about the Yaesu transceivers
with the ORANGE button (some call it red)? Any Yaesu owner has stepped up to
the plate and said he just uses his orange button on (ALWAYS at full power, max
RF power knob fully clockwise).... and explains and extolls that strategy to
put out cleaner signals???
Someone, please just state how much the orange button Yaesu-s help, preferably compared to the K3.
Thanks mucho,
73, Charly
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