[Amps] FT8 power with the KPA1500

Wed Jul 7 17:56:58 EDT 2021

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 at 50V-1000W out ( dissipation is 1100W) , and 
49A at 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 at 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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> Today's Topics:
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>     1. Relay Burnisher (jim.thom jim.thom at telus.net)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Tue, 6 Jul 2021 09:33:44 -0700
> From: "jim.thom jim.thom at telus.net" <jim.thom at telus.net>
> To: amps at contesting.com
> Subject: [Amps] Relay Burnisher
> Message-ID:
> 	<CAB4ZMgu1qNx0_x3g9T0RqyLZmQhMrKC870h7Y=TMAH681pFj8g at mail.gmail.com>
> Content-Type: text/plain; charset="UTF-8"
>
> Date: Mon, 5 Jul 2021 19:22:55 +0000
> From: Kevin Adam <n9iww at LIVE.COM>
> To: "amps at contesting.com" <amps at 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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-- 
Dave Manuals at ArtekManuals.com www.ArtekManuals.com

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