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KPA500 & Drake TR7

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KPA500 & Drake TR7

Greetings from Barcelona
I have here a K3-KPA500 setup that runs great
I also have a TR7 and I am thinking about using it together with the KPA500 The obvious problem: The TR7 delivers a lot of watts (200 pep).
Is it an idea to discard? Or is there any reasonable approach to? ALC control is not a good idea I think
As an alternative (500-1000 W), is there any small (in size) linear to consider? I don't want to go back to the big tube linears. The KPA500 is great for what I want to have here.
73s de Marcel - EA3IN
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Bob McGraw - K4TAX

Re: KPA500 & Drake TR7

If you can run 200 watts PEP with the TR7, why run a 500 watt amp?
Otherwise, you'll need a 10dB attenuator between the TR7 and the
KPA500. Hence turn 180 watts of RF from the TR7 into heat as it takes
only about 20 watts to drive the KPA500 to rated output.

73

Bob, K4TAX

On 1/12/2019 11:59 AM, Marcel Jorba via Elecraft wrote:

> Greetings from Barcelona
> I have here a K3-KPA500 setup that runs great
> I also have a TR7 and I am thinking about using it together with the KPA500 The obvious problem: The TR7 delivers a lot of watts (200 pep).
> Is it an idea to discard? Or is there any reasonable approach to? ALC control is not a good idea I think
> As an alternative (500-1000 W), is there any small (in size) linear to consider? I don't want to go back to the big tube linears. The KPA500 is great for what I want to have here.
> 73s de Marcel - EA3IN
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
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Re: KPA500 & Drake TR7

In reply to this post by Elecraft mailing list

Hello EA3IN,

There is a 1 kilowatt solid state amplifier, using NXP 188 final power
transistors, built in England.

Please see LinearAmp company, model Gemini HF-1K amplifier. I believe
that DXshop is the

vendor. Regards, bp. K2AYA.

On 1/12/19 12:59 PM, Marcel Jorba via Elecraft wrote:

Don Wilhelm

Re: KPA500 & Drake TR7

In reply to this post by Elecraft mailing list

Marcel,

Can you add a "Power Control" to the TR7?
It may be as easy as applying a constant negative voltage to the ALC
input. That constant ALC voltage will not cause the problems
encountered when using the dynamic ALC voltage that is applied from the
amplifier.

73,
Don W3FPR

On 1/12/2019 12:59 PM, Marcel Jorba via Elecraft wrote:
> Greetings from Barcelona
> I have here a K3-KPA500 setup that runs great
> I also have a TR7 and I am thinking about using it together with the KPA500 The obvious problem: The TR7 delivers a lot of watts (200 pep).
> Is it an idea to discard? Or is there any reasonable approach to? ALC control is not a good idea I think
> As an alternative (500-1000 W), is there any small (in size) linear to consider? I don't want to go back to the big tube linears. The KPA500 is great for what I want to have here.
> 73s de Marcel - EA3IN
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ab2tc

Re: KPA500 & Drake TR7

Hi Marcel and Don,

The TR7 is rated at 250W *input*. See here:

https://www.universal-radio.com/catalog/hamhf/tr7.html

With typical efficiencies seen in solid state PAs it is probably rated at no
more than 100W output, so the KPA500 should give you noticeably more power.
Anyway, Don's suggestion to use a constant (but variable) negative voltage
applied to the ALC input of the TR7 should work. Make sure that it is well
filtered, as any noise or hum will (AM) modulate the RF signal.

AB2TC - Knut

Don Wilhelm wrote

> Marcel,
>
> Can you add a "Power Control" to the TR7?
> It may be as easy as applying a constant negative voltage to the ALC
> input. That constant ALC voltage will not cause the problems
> encountered when using the dynamic ALC voltage that is applied from the
> amplifier.
>
> 73,
> Don W3FPR
>
> On 1/12/2019 12:59 PM, Marcel Jorba via Elecraft wrote:
>> Greetings from Barcelona
>> I have here a K3-KPA500 setup that runs great
>> I also have a TR7 and I am thinking about using it together with the
>> KPA500 The obvious problem: The TR7 delivers a lot of watts (200 pep).
>> Is it an idea to discard? Or is there any reasonable approach to? ALC
>> control is not a good idea I think
>> As an alternative (500-1000 W), is there any small (in size) linear to
>> consider? I don't want to go back to the big tube linears. The KPA500 is
>> great for what I want to have here.
>> 73s de Marcel - EA3IN
> <snip>

--
Sent from: http://elecraft.365791.n2.nabble.com/
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K9MA

Re: KPA500 & Drake TR7

On 1/13/2019 12:35, ab2tc wrote:
> With typical efficiencies seen in solid state PAs it is probably rated at no
> more than 100W output,

Actually, tube amplifiers can be quite a bit more efficient than solid
state ones. The theoretical limit for class B is around 70 percent, a
practical limit probably around 60. So, the TR7 might put out 150 W.

73,

Scott K9MA

--
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ab2tc

Re: KPA500 & Drake TR7

Hi again,

True, but the TR7 is all solid state, including the finals. See here:

http://www.wb4hfn.com/DRAKE/DrakeArticles/InsideTheTR7/Inside_The_TR7-01.htm

According to that article Drake claims 130-150W output for bands at above
20m and 60-100W on 80-15m.

Boy, is that transceiver ever jam-packed! Wonder how it does cooling-wise.

AB2TC - Knut

K9MA wrote

> On 1/13/2019 12:35, ab2tc wrote:
>> With typical efficiencies seen in solid state PAs it is probably rated at
>> no
>> more than 100W output,
>
> Actually, tube amplifiers can be quite a bit more efficient than solid
> state ones. The theoretical limit for class B is around 70 percent, a
> practical limit probably around 60. So, the TR7 might put out 150 W.
>
> 73,
>
> Scott K9MA
>
> --
> Scott K9MA

> k9ma@

>
> <snip>

--
Sent from: http://elecraft.365791.n2.nabble.com/
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ab2tc

Re: KPA500 & Drake TR7

Hi again,

I totally mangled the 2nd statement. Corrected below.

Knut

ab2tc wrote

Grant Youngman-2

Re: KPA500 & Drake TR7

In reply to this post by ab2tc

As an aside on the TR-7 (one of my all-time favorite radios), Drake generally limiting output power to about 120W (adjusted on 20M) to keep the PA healthy long term. While the PA is capable of 150-200W output, it was certainly not recommended.

As to cooling, there was an optional fan to cool the PA for modes with high duty cycle (RTTY, etc).

Grant NQ5T
K3 #2091 KX3 #8342

> On Jan 13, 2019, at 2:14 PM, ab2tc <[hidden email]> wrote:
>
> Hi again,
>
> True, but the TR7 is all solid state, including the finals. See here:
>
> http://www.wb4hfn.com/DRAKE/DrakeArticles/InsideTheTR7/Inside_The_TR7-01.htm
>
> According to that article Drake claims 130-150W output for bands at above
> 20m and 60-100W on 80-15m.
>
> Boy, is that transceiver ever jam-packed! Wonder how it does cooling-wise.
>
> AB2TC - Knut
>

Wes Stewart-2

Re: KPA500 & Drake TR7

In reply to this post by ab2tc

Drake rated the TR7 by input power as was common then. 250W. They recommended
a fan kit for high duty cycle RTTY operation.

I owned one for years and it was a wonderful radio. The only issue was
tin-plated pins (sound familiar) on the interface between the main circuity and
the digital readout board. Some contact cleaner and massaging the pins after
loosening the mounting screws usually fixed it for another six months or so.

There was no internal provision for split operation, they sold an external VFO.
I built my own.

Wes N7WS

On 1/13/2019 12:14 PM, ab2tc wrote:

> Hi again,
>
> True, but the TR7 is all solid state, including the finals. See here:
>
> http://www.wb4hfn.com/DRAKE/DrakeArticles/InsideTheTR7/Inside_The_TR7-01.htm
>
> According to that article Drake claims 130-150W output for bands at above
> 20m and 60-100W on 80-15m.
>
> Boy, is that transceiver ever jam-packed! Wonder how it does cooling-wise.
>
> AB2TC - Knut
>
>
> K9MA wrote
>> On 1/13/2019 12:35, ab2tc wrote:
>>> With typical efficiencies seen in solid state PAs it is probably rated at
>>> no
>>> more than 100W output,
>> Actually, tube amplifiers can be quite a bit more efficient than solid
>> state ones. The theoretical limit for class B is around 70 percent, a
>> practical limit probably around 60. So, the TR7 might put out 150 W.
>>
>> 73,
>>
>> Scott K9MA
>>
>> --
>> Scott K9MA
>> k9ma@
>> <snip>
>
>
>
>
> --
> Sent from: http://elecraft.365791.n2.nabble.com/
> ______________________________________________________________
> Elecraft mailing list
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>

Elecraft mailing list

Re: KPA500 & Drake TR7

In reply to this post by Elecraft mailing list

Thanks to all of for your prompt answers
On CW it works great thanks to the carrier adjustment control

On SSB: it goes to 150W out very easy
Yes it is just for fun.
The K3 is great but the TR7 is funny and special.

One last question: Someone suggested to use a 9V battery with a pot to inject a constant negative voltage in to the TR7. But any idea about the maximum voltage?
Regrds
Marcel

On Saturday, January 12, 2019, 6:59:32 PM GMT+1, Marcel Jorba <[hidden email]> wrote:

Greetings from Barcelona
I have here a K3-KPA500 setup that runs great
I also have a TR7 and I am thinking about using it together with the KPA500 The obvious problem: The TR7 delivers a lot of watts (200 pep).
Is it an idea to discard? Or is there any reasonable approach to? ALC control is not a good idea I think
As an alternative (500-1000 W), is there any small (in size) linear to consider? I don't want to go back to the big tube linears. The KPA500 is great for what I want to have here.
73s de Marcel - EA3IN
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Don Wilhelm

Re: KPA500 & Drake TR7

Marcel,

About the maximum voltage, that might be in the TR7 specifications.
OTOH, start with the pot at a low voltage and increase it until you
achieve the results that you want.

The K3 EXT ALC default threshold is -4.0 volts, so that may be a good
starting point for your experiments.

73,
Don W3FPR

On 1/13/2019 5:19 PM, Marcel Jorba via Elecraft wrote:
> Thanks to all of for your prompt answers
> On CW it works great thanks to the carrier adjustment control
>
> On SSB: it goes to 150W out very easy
> Yes it is just for fun.
> The K3 is great but the TR7 is funny and special.
>
>
> One last question: Someone suggested to use a 9V battery with a pot to inject a constant negative voltage in to the TR7. But any idea about the maximum voltage?
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Martin Sole-3

Re: KPA500 & Drake TR7

It's worthwhile noting that either adjusting the internal ALC to limit
power or providing some external means to control it is really quite
essential with some of the early solid state and certainly many of the
hybrid radios. Most of these radios had NO proper power control in SSB.
Whilst the carrier control can be used to control CW power, on SSB they
typically run wide open up to where the ALC kicks in and so only mic
gain essentially sets power. Since that is a linear control it will
amplify louder noises up to the ALC threshold. So your voice might
ordinarily produce a peak of 20-30 watts if you have the control set
just so but any noise will produce substantially more.

I don't know what the KPA500 says to 100watts + at its input, hopefully
it is quite graceful about it.

Martin, HS0ZED

On 14/01/2019 02:10, Don Wilhelm wrote:

> Marcel,
>
> About the maximum voltage, that might be in the TR7 specifications.
> OTOH, start with the pot at a low voltage and increase it until you
> achieve the results that you want.
>
> The K3 EXT ALC default threshold is -4.0 volts, so that may be a good
> starting point for your experiments.
>
> 73,
> Don W3FPR
>
> On 1/13/2019 5:19 PM, Marcel Jorba via Elecraft wrote:
>> Thanks to all of for your prompt answers
>> On CW it works great thanks to the carrier adjustment control
>>
>> On SSB: it goes to 150W out very easy
>> Yes it is just for fun.
>> The K3 is great but the TR7 is funny and special.
>>
>>
>> One last question: Someone suggested to use a 9V battery with a pot
>> to inject a constant negative voltage in to the TR7. But any idea
>> about the maximum voltage?
> ______________________________________________________________
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Gary Smith-2

Re: KPA500 & Drake TR7

In reply to this post by K9MA

I hesitate to answer to this, it's been so
long since I had a TR7 (My 2nd rig) and my
memory of it is not clear.

Given this disclaimer, I believe you'll
find an adjustable piece, two wafers with
a rectangular key hole in the center part
to turn it. Cap or resistance, I don't
recall what it was, but it controlled the
output and you could lower it way down or
get more than the rated output with it (at
the expense of the transistors if you
pushed it too long).

I wish I could remember exactly where it
was, but I believe it was on the heatsink
or close to it at the back side of the
rig. Might have been blue, I'm not sure,
maybe it was accessible from the outside
of the radio, from the bottom rear? I
think I'd remember it if I saw the TR7
again, the adjustment was in plain sight.

I suspect if you backed it down you'll be
fine with the output from the KPA-500.

For some time the TR7 was used for EME,
the person who bought mine was modding it
for that and perhaps in an EME group
someone might have good knowledge of the
TR7 and where this was exactly located.

73,

Gary
KA1J

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