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[K2] Safely running 100% key-down modes

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K1FFX

[K2] Safely running 100% key-down modes

I starting to use my K2/100 in two 100% key-down modes, JT-65 and PSK-31. What
should I be keeping in mind in protecting the output stage for the K2 and for the KPA100?

For JT-65, since it is a QRP mode, I'm running at about 5 watts, and transmissions are
limited to about 45 seconds. So, I'm hoping that K2's output transistors will not be stressed
in this mode.

But, how about PSK-31? I'd like to run about 20 watts and each transmission could easily
be 3 or so minutes. I don't know at what output power the base K2 runs when the KPA100
kicks in (i.e., at above 10 watts). I assume that normally the KPA100 will be loafing at 20
watts, but I'm not sure the impact of 100% key down on its output stage.

I'd appreciate any guidance in keeping the K2/100 "safe" in these modes.

Thanks -

Bruce K1FFX

Bruce Rosen
K1FFX
K2/100 6982 KSB2 KAT100-1 KAF2 KIO2

Don Wilhelm-4

Re: [K2] Safely running 100% key-down modes

Bruce,

The base K2 power is proportional to the power out of the KPA100 - so if
the KPA100 is running at 20 watts, the base K2 is driving at about 2 watts.

You can run 100% duty cycle transmissions safely at 35 watts, and could
probably push it to 50 watts if you provide auxiliary cooling for the
KPA100 and the receive periods are long enough to allow the heatsink to
cool. You could increase the cooling by placing a muffin fan over the
heat sink.

It is heat that will create problems - you can always use your fingers
as an indicator. If the surface of the heat sink is too hot to hold
your fingers on it, it is likely too hot. Don't forget that the base K2
PA transistors are on the bottom rear.

73,
Don W3FPR

On 12/26/2013 12:06 PM, K1FFX wrote:

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EricJ-2

Re: [K2] Safely running 100% key-down modes

In reply to this post by K1FFX

I run JT9 and JT65 very frequently with the K2/100. Most of the time, I
run 5 watts. If needed I'll crank it up to 20 watts, so I can assure you
it's quite safe at that power level.

When the linear kicks in the K2 drive power to the linearis
proportional, so if you are within the duty cycle of the linear, you are
within the duty cycle of the K2 barefoot.

At 20 watts the fan usually comes on after about 30 seconds of TX and
stays on for the remainder of the TX cycle and much of the RX cycle. At
around 25-30 watts, the fan is on all the time, but I don't ever run it
that high. The JT modes are meant for weak signals so I only work weak
signals and find that at 15-20 watts I'm giving very close to the same
signal report I receive.

For PSK, I stick to the same power levels as JT modes. I don't run PSK
very often because it's not as interesting to me. I lost patience with
brag tapes in the RTTY days. Now they provide model numbers of every
rig, every radio accessory and every computer specification including
version numbers of software even if they aren't using that gear for the
QSO. Sort of a shopping list for burglars.

The K2 does a very nice job with all the digital modes.

Eric
KE6US

On 12/26/2013 9:06 AM, K1FFX wrote:

> I starting to use my K2/100 in two 100% key-down modes, JT-65 and PSK-31.
> What
> should I be keeping in mind in protecting the output stage for the K2 and
> for the KPA100?
>
> For JT-65, since it is a QRP mode, I'm running at about 5 watts, and
> transmissions are
> limited to about 45 seconds. So, I'm hoping that K2's output transistors
> will not be stressed
> in this mode.
>
> But, how about PSK-31? I'd like to run about 20 watts and each transmission
> could easily
> be 3 or so minutes. I don't know at what output power the base K2 runs when
> the KPA100
> kicks in (i.e., at above 10 watts). I assume that normally the KPA100 will
> be loafing at 20
> watts, but I'm not sure the impact of 100% key down on its output stage.
>
> I'd appreciate any guidance in keeping the K2/100 "safe" in these modes.
>
> Thanks -
>
> Bruce K1FFX
>
>
>
>
> -----
> Bruce Rosen
> K1FFX
> K2/100 6982 KSB2 KAT100-1
>
> --
> View this message in context: http://elecraft.365791.n2.nabble.com/K2-Safely-running-100-key-down-modes-tp7582081.html
> Sent from the Elecraft mailing list archive at Nabble.com.
> ______________________________________________________________
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>

aj4tf

Re: [K2] Safely running 100% key-down modes

In reply to this post by Don Wilhelm-4

Second that on the muffin fan. I have one sitting on top of the KPA100 heatsink, and when running 50-60 watts in long duty cycle modes (i.e. RTTY), very seldom does the internal KPA100 fan ever need to activate.

73, de AJ4TF

Bill Coleman-2

Re: [K2] Safely running 100% key-down modes

In reply to this post by K1FFX

On Dec 26, 2013, at 12:06 PM, K1FFX <[hidden email]> wrote:

> I starting to use my K2/100 in two 100% key-down modes, JT-65 and PSK-31.
> What should I be keeping in mind in protecting the output stage for the K2 and
> for the KPA100?

I’ve used the K2/100 in RTTY and PSK31, even for contests. As designed, I don’t believe that Elecraft recommends running more than about 25 watts out in these 100% duty cycle modes. You can run 50-100 watts for short periods, but there really isn’t enough cooling.

I modified my K2/100 by adding a small fan, mounted on rubber feet that sits on top of the heat sink, right where the power transistors are. It blows air down into the heat sink continuously. I have no problem running 50 watts RTTY in this configuration for hours and hours, and could probably run 100 watts with a slightly larger fan.

> For JT-65, since it is a QRP mode, I'm running at about 5 watts, and
> transmissions are limited to about 45 seconds. So, I'm hoping that K2's output transistors
> will not be stressed in this mode.

If you run less than 11 watts, the KPA100 deactivates, so you are just running the base K2 only. You’d be better off running 11-25 watts, and using the KPA100, than stressing the K2 output transistors.

> But, how about PSK-31? I'd like to run about 20 watts and each transmission
> could easily
> be 3 or so minutes. I don't know at what output power the base K2 runs when
> the KPA100
> kicks in (i.e., at above 10 watts). I assume that normally the KPA100 will
> be loafing at 20
> watts, but I'm not sure the impact of 100% key down on its output stage.

Should work great.

Bill Coleman, AA4LR, PP-ASEL Mail: [hidden email]
Quote: "Boot, you transistorized tormentor! Boot!"
-- Archibald Asparagus, VeggieTales

Bill Coleman, AA4LR, PP-ASEL Mail: [hidden email]
Web: http://boringhamradiopart.blogspot.com
Quote: "Not within a thousand years will man ever fly!"
-- Wilbur Wright, 1901

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