K3 power amp 2SC2782

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K3 power amp 2SC2782

HankP
Anyone know if the Toshiba 2SC2782 transistors used in the K3 power amp
have internal matching (mos cap and wirebonds ) ?

Or did the K3 power amp ever use Motorola MRF247 transistors ?


Hank K7HP

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Re: K3 power amp 2SC2782

Robert Friess
Hank,

The 2SC2782 is not internally matched and is the only part ever used in the
KPA3.  The KPA3A uses MOSFETs.

73,
Bob, N6CM

On Sat, Jan 5, 2019 at 11:04 AM HP <[hidden email]> wrote:

> Anyone know if the Toshiba 2SC2782 transistors used in the K3 power amp
> have internal matching (mos cap and wirebonds ) ?
>
> Or did the K3 power amp ever use Motorola MRF247 transistors ?
>
>
> Hank K7HP
>
> ______________________________________________________________
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Re: K3 power amp 2SC2782

K9MA
I've always felt that the KPA3 in my K3 was marginal.  For example, I've
never been able to get more than about 80 W out of it on 15 meters. (And
that's at about 14.5 V) Is the KPA3A any better?

73,
Scott K9MA

On 1/5/2019 15:23, Robert Friess wrote:

> Hank,
>
> The 2SC2782 is not internally matched and is the only part ever used in the
> KPA3.  The KPA3A uses MOSFETs.
>
> 73,
> Bob, N6CM
>
> On Sat, Jan 5, 2019 at 11:04 AM HP <[hidden email]> wrote:
>
>> Anyone know if the Toshiba 2SC2782 transistors used in the K3 power amp
>> have internal matching (mos cap and wirebonds ) ?
>>
>> Or did the K3 power amp ever use Motorola MRF247 transistors ?
>>
>>
>> Hank K7HP
>>
>> ______________________________________________________________
>>

--
Scott  K9MA

[hidden email]

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Re: K3 power amp 2SC2782

ab2tc
Hi,

How are you measuring your actual output and in which mode are you testing
it? I have a K3S and a K3 souped up to near K3S but still with the original
transmitter chain. I have no problem achieving 100W with either one of them
into a factory calibrated LP100A, testing it in FM mode. Overall I think the
original KPA3 with bipolars is at least as good a transmitter as the new
FET-based KPA3A. The transmitter chain in the K3S has been "recalled" twice
in order to improve the 3rd order IMD. The original KPA3 has remained
unmodified as far as I know.

Heve you done the wattmeter calibration based on a wattmeter you trust, such
as the LP100A (by Telepost.inc) and have you done the TX gain calibration? A
properly functioning K3 or K3S should have no problem achieving 100W
provided the power supply is making 13.8V or more *at the transceiver*.

AB2TC - Knut


K9MA wrote

> I've always felt that the KPA3 in my K3 was marginal.  For example, I've
> never been able to get more than about 80 W out of it on 15 meters. (And
> that's at about 14.5 V) Is the KPA3A any better?
>
> 73,
> Scott K9MA
>
> On 1/5/2019 15:23, Robert Friess wrote:
>> Hank,
> <snip>





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Re: K3 power amp 2SC2782

ab2tc
Hi again,

One thought: What is your firmware version? I now remember that there was
one version that had a problem delivering full power on 15m only. This has
long been fixed. Make sure you have the latest.

AB2TC - Knut


ab2tc wrote
> Hi,
>
> How are you measuring your actual output and in which mode are you testing
> it? I have a K3S and a K3 souped up to near K3S but still with the
> original
> <snip>





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Re: K3 power amp 2SC2782

Wes Stewart-2
In reply to this post by K9MA
I have not observed a low power issue in my K3.  OTOH, in my experience the K3S
PA has been a huge disappointment.  One reason for buying a K3S was a hope that
the TX IMD would be improved with FETs.  This would no doubt have been true if
Elecraft designed the radio for 50 VDC.

Wes  N7WS

On 1/5/2019 3:16 PM, K9MA wrote:

> I've always felt that the KPA3 in my K3 was marginal.  For example, I've never
> been able to get more than about 80 W out of it on 15 meters. (And that's at
> about 14.5 V) Is the KPA3A any better?
>
> 73,
> Scott K9MA
>
> On 1/5/2019 15:23, Robert Friess wrote:
>> Hank,
>>
>> The 2SC2782 is not internally matched and is the only part ever used in the
>> KPA3.  The KPA3A uses MOSFETs.
>>
>> 73,
>> Bob, N6CM
>>
>> On Sat, Jan 5, 2019 at 11:04 AM HP <[hidden email]> wrote:
>>
>>> Anyone know if the Toshiba 2SC2782 transistors used in the K3 power amp
>>> have internal matching (mos cap and wirebonds ) ?
>>>
>>> Or did the K3 power amp ever use Motorola MRF247 transistors ?
>>>
>>>
>>> Hank K7HP
>>>
>>> ______________________________________________________________
>>>
>

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Re: K3 power amp 2SC2782

ab2tc
Hi Wes,

Agreed. In my view FETs are a mistake at the 14V level. The old K3 bipolar
PA is much better (but still not good).

Knut - AB2TC



Wes Stewart-2 wrote

> I have not observed a low power issue in my K3.  OTOH, in my experience
> the K3S
> PA has been a huge disappointment.  One reason for buying a K3S was a hope
> that
> the TX IMD would be improved with FETs.  This would no doubt have been
> true if
> Elecraft designed the radio for 50 VDC.
>
> Wes  N7WS
>
> On 1/5/2019 3:16 PM, K9MA wrote:
>> I've always felt that the KPA3 in my K3 was marginal.  For example, I've
>> never
> <snip>





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Re: K3 power amp 2SC2782

Roger-3
Examples of "14V" radios using RD100HHF1 final transistors and delivering good & stable results:

ANAN 100,200 & 7000 series (w/o PureSignal) (3rd order IMD -30 dBc  average (-36dB referred to one tone)); see AB4OJs test
Kenwood TS 890S (3rd order IMD -32 dBc (-38 dB referred to one tone))

YAESU and ICOM are running the same transistors in some of their models. I am not promoting any brand but it is nothing "magic" or "bad" with MOSFETS being used at 14 V. Sure their advantage of having even better IMD characteristics at higher voltages cannot be used in a 14 V system.

Roger/DL5RBW

-----Original Message-----
From: [hidden email] [mailto:[hidden email]] On Behalf Of ab2tc
Sent: Sunday, January 06, 2019 1:42 AM
To: [hidden email]
Subject: Re: [Elecraft] K3 power amp 2SC2782

Hi Wes,

Agreed. In my view FETs are a mistake at the 14V level. The old K3 bipolar PA is much better (but still not good).

Knut - AB2TC



Wes Stewart-2 wrote

> I have not observed a low power issue in my K3. OTOH, in my experience
> the K3S PA has been a huge disappointment. One reason for buying a K3S
> was a hope that the TX IMD would be improved with FETs. This would no
> doubt have been true if Elecraft designed the radio for 50 VDC.
>
> Wes N7WS
>
> On 1/5/2019 3:16 PM, K9MA wrote:
>> I've always felt that the KPA3 in my K3 was marginal. For example,
>> I've never
> <snip>





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