Ron
For starters the KPA1500 is spec'd at 1500W PEP 100% ICAS duty cycle
modulation for FT8 and RTTY ( page 8 of the manual) Max 5 minutes
continuous key down ( 50 seconds on 50MHz)
Unlike tube amps, LDMOS amps are "optimally pre-matched" to 50 ohms at
full output ( no knobs to twist) and actually dissipate as much power
(or more) at 1000W as they do at 1500W. There is documentation for this
but the link escapes me at moment, perhaps on QRZ.com or EHam. You can
actually measure the dissipation in watts ....... (PA current * 50
volts)-Pout
By example on 20M i draw 42A@50V-1000W out ( dissipation is 1100W) , and
49A@50V-1500W (dissipation 950W)
The rule of thumb is keep it cool I run mine at 1500W (1250 on 6M) on
FT8 for 5 min. at a time if necessary ( typically for a new band/country).
You can use the menus to program a higher fan speed . I have programmed
the PF1 and PF2 on the front panel to engage a higher or lower fan
speed. as required
All that being said I typically do not run over 500W on FT8 A false
economy though from a dissipation point of view ( 31A@50V-500W =1050W
dissipation) depending on conditions and am always surprised that I
have changed bands and forgotten to switch the amp out of standby and
make many many FT8 Contacts with 15 to 25watts from the exciter only,
which was the original premise of the FT modes to begin with.
Said another way FT modes are no harder on the amp ( probably not quite
as hard ) as RTTY rag chewing. The enemy is heat ...make sure the amp
has unrestricted airflow and keep an eye on the temperature
Hope this gives you some insight
Dave
NR1DX
On 7/7/2021 4:10 PM, Ron wrote:
How much power can I run on FT8/FT4 with my new KPA1500 ?
A friend with the Expert amp limits his output to 1000 watts.
Ron KH6DV
Kaneohe Bay Hawaii
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From: amps-request@contesting.com
Sent: Wednesday, July 7, 2021 6:25 AM
To: amps@contesting.com
Subject: Amps Digest, Vol 223, Issue 8
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Today's Topics:
1. Relay Burnisher (jim.thom jim.thom@telus.net)
----------------------------------------------------------------------
Message: 1
Date: Tue, 6 Jul 2021 09:33:44 -0700
From: "jim.thom jim.thom@telus.net" <jim.thom@telus.net>
To: amps@contesting.com
Subject: [Amps] Relay Burnisher
Message-ID:
<CAB4ZMgu1qNx0_x3g9T0RqyLZmQhMrKC870h7Y=TMAH681pFj8g@mail.gmail.com>
Content-Type: text/plain; charset="UTF-8"
Date: Mon, 5 Jul 2021 19:22:55 +0000
From: Kevin Adam <n9iww@LIVE.COM>
To: "amps@contesting.com" <amps@contesting.com>
Subject: [Amps] Relay Burnisher
< Burnisher with Black Plastic Insulated Handle, For Fine Contacts, 3"
Length x 3/16" <Width x 0.007" Thickness (3 count)
https://www.amazon.com/Jonard-OB-1-Burnisher-Insulated-Thickness/dp/B006C47JOI/ref=sr_1_4?dchild=1&keywords=file+relay&qid=1625512832&sr=8-4
<N9IWW
## we used hundreds of the exact same burnishing tool in the telco I
worked at. This was back in the electromechanical days. It was the NA
gold standard for burnishing relay contacts. Back then, they came in 10
or 20 packs. It's an ultra fine surface, so it doesn't destroy any
plating. What worked better for cleaning out dirty contacts was
...microscrubs...soaked in your favourite cleaning solution. 1-2 passes,
and contacts were like new.
I would be a bit leery using the burnishing tool on any gold plated
contacts though. My real fix for these relay issues is to swap to a
gigavc GH-1 ceramic vac relay for both the input and also the output.
Then an opto isolator for the cut off bias. I also use an opto
isolator for the soft key...or use your favourite switch transistor.
3PDT mech relays issues gone forever. Then it's qsk on cw if you want,
and no more tune and or load arcing due to slow mech relays, or mech relays
that are not quite sequenced correctly. IE: applying drive to the amp a
split second before the ant is connected on the output side.
Plus you can run a kw through the amp when on bypass mode. I use that
feature, so I can calibrate the wattmeter in my drake L4B amps. To do
that, I have to use one amp to feed a kw into the 2nd amp, with 2nd amp in
bypass mode, powered down, on its side, and bottom lid off, so I can get
to the calibration pots. I also use that feature since I string several
L4Bs in series...tuned up on diffrerant bands or ssb and cw on the same
band. . A rotary switch in the key line from Xcvr, ensures only one amp
can ever be in operate mode...simple mech interlock.
Jim VE7RF
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