New from Elecraft: KPA1500 amplifier with built-in ATU, separate power supply

It is very easy to put a hairpin coil on your top band vertical and bring
the resonant SWR to 1:1. This should give you much more usable SWR
bandwidth for the KPA1500. Many commercial tube amplifiers will only
tolerate 2:1 SWR.

John KK9A


From Wes Stewart n7ws
Fri Apr 21 13:11:12 EDT 2017

I'm not necessarily defining a personal situation.  But almost any 80 or 160
antenna will suffice as an example.

I am currently constructing a vertical for those bands.  The model shows
2:1 on
160 at resonance and >3:1 just 60 KHz away and this is with considerable
ground
loss.  Less loss would equal lower BW.  With quarter wave resonance on 80
at 3.6
MHz it exceeds 3:1 at 3.8 MHz and is nearly 7:1 at 4.0.

Transmission line loss is a non-issue with 7/8" Heliax.

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[Wes Stewart-2]

Without modeling it, I would guess that it will actually narrow the matched BW
and it makes it a single band antenna at the same time.

My Drake L4-B would drive anything.  When I decided I needed a new challenge
(9BDXCC) I wanted to get on 160.  Of course the Drake didn't cover 160 and my
then K3, now K3S doesn't have a tuner.  So I added some wire to the ends of the
80-meter inverted V.  This meant that I didn't have an 80-meter antenna but the
Drake would drive it anyway.  Currently, with a KPA500 and KAT500 I have modest
power on 160 but the KAT500 chokes on 80 at above 200-300 Watts.

Hence the new vertical for next season.

On 4/21/2017 11:10 AM, [hidden email] wrote:

> It is very easy to put a hairpin coil on your top band vertical and bring
> the resonant SWR to 1:1. This should give you much more usable SWR
> bandwidth for the KPA1500. Many commercial tube amplifiers will only
> tolerate 2:1 SWR.
>
> John KK9A
>
>
> >From Wes Stewart n7ws
> Fri Apr 21 13:11:12 EDT 2017
>
> I'm not necessarily defining a personal situation.  But almost any 80 or 160
> antenna will suffice as an example.
>
> I am currently constructing a vertical for those bands.  The model shows
> 2:1 on
> 160 at resonance and >3:1 just 60 KHz away and this is with considerable
> ground
> loss.  Less loss would equal lower BW.  With quarter wave resonance on 80
> at 3.6
> MHz it exceeds 3:1 at 3.8 MHz and is nearly 7:1 at 4.0.
>
> Transmission line loss is a non-issue with 7/8" Heliax.
>
> ______________________________________________________________
> Elecraft mailing list
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>

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[Grant Youngman-2]

There seems to be some disappointment that a relatively compact wide-range auto-tuner at legal limit CCS (or even ICAS) is not included.  I don’t consider this a negative.

1.  A legal limit "LOW LOSS" CCS tuner using the build methods of most typical ham auto-tuners would be large and heavy with BIG toroids or air-wound inductors and probably vacuum caps, and expensive.  The usual supposed wide-range high power auto stuff is ICAS at best — with the operative word being “Intermittent”, unless you’re trying to boil water or vaporize circuit board traces.

2.  There are many ways to bring any antenna/feedline's Z0 to something that a reasonably-sized affordable auto-tuner can handle at not too great a feed line SWR.  Not the least of which is to feed a commercial old fashioned mechanical tuner with heavy-rated components that can handle the reflected power from whatever bobbie-pin you’re trying to match without just melting all the plastic in the tuner if you key down for a bit too long.

The Drake L4B (and most well built tube amps) have wide range Pi-networks with heavy components (large air-wound inductors, caps, switch contacts) that can handle the stress of high SWR at the amplifier’s output.  But even that won’t successfully match anything you throw at it (well, except for the Johnson Ranger, but thats not the subject).  Look at the innards of an MN2000 or Millen 92200 to get a feel for it.

In most cases you can use a (good, not fine junk) mechanical tuner (knobs you have to turn, meters you have to read) to set the SWR in a band to somewhere in the vicinity of 1:1 at the midpoint of operating interest, and most well made internal tuners can manage the band edges in that case — when the load is non-resonant and presents a high SWR.

I suspect a real auto-tuner that can handle just about anything at 1500 watts at key down for a long period would take at least another KPA1500 sized box.

(Just another curmudgeonly opine)


Grant NQ5T
K3 #2091, KX3 #8342

> On Apr 21, 2017, at 2:57 PM, Wes Stewart <[hidden email]> wrote:
>
> Without modeling it, I would guess that it will actually narrow the matched BW and it makes it a single band antenna at the same time.
>
> My Drake L4-B would drive anything.  When I decided I needed a new challenge (9BDXCC) I wanted to get on 160.  Of course the Drake didn't cover 160 and my then K3, now K3S doesn't have a tuner.  So I added some wire to the ends of the 80-meter inverted V.  This meant that I didn't have an 80-meter antenna but the Drake would drive it anyway.  Currently, with a KPA500 and KAT500 I have modest power on 160 but the KAT500 chokes on 80 at above 200-300 Watts.
>
> Hence the new vertical for next season.
>
> On 4/21/2017 11:10 AM, [hidden email] <mailto:[hidden email]> wrote:
>> It is very easy to put a hairpin coil on your top band vertical and bring
>> the resonant SWR to 1:1. This should give you much more usable SWR
>> bandwidth for the KPA1500. Many commercial tube amplifiers will only
>> tolerate 2:1 SWR.
>>
>> John KK9A
>>
>>
>>

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[Bill K9YEQ]

I see the internal a plus, limiting, I would expect faults when there is high swr.  Smart move! Safety and buyers $'s.

73,
Bill
K9YEQ

-----Original Message-----
From: Elecraft [mailto:[hidden email]] On Behalf Of GRANT YOUNGMAN
Sent: Friday, April 21, 2017 3:00 PM
To: Elecraft Reflector <[hidden email]>
Subject: Re: [Elecraft] New from Elecraft: KPA1500 amplifier with built-in ATU, separate power supply

There seems to be some disappointment that a relatively compact wide-range auto-tuner at legal limit CCS (or even ICAS) is not included.  I don’t consider this a negative.

1.  A legal limit "LOW LOSS" CCS tuner using the build methods of most typical ham auto-tuners would be large and heavy with BIG toroids or air-wound inductors and probably vacuum caps, and expensive.  The usual supposed wide-range high power auto stuff is ICAS at best — with the operative word being “Intermittent”, unless you’re trying to boil water or vaporize circuit board traces.

2.  There are many ways to bring any antenna/feedline's Z0 to something that a reasonably-sized affordable auto-tuner can handle at not too great a feed line SWR.  Not the least of which is to feed a commercial old fashioned mechanical tuner with heavy-rated components that can handle the reflected power from whatever bobbie-pin you’re trying to match without just melting all the plastic in the tuner if you key down for a bit too long.

The Drake L4B (and most well built tube amps) have wide range Pi-networks with heavy components (large air-wound inductors, caps, switch contacts) that can handle the stress of high SWR at the amplifier’s output.  But even that won’t successfully match anything you throw at it (well, except for the Johnson Ranger, but thats not the subject).  Look at the innards of an MN2000 or Millen 92200 to get a feel for it.

In most cases you can use a (good, not fine junk) mechanical tuner (knobs you have to turn, meters you have to read) to set the SWR in a band to somewhere in the vicinity of 1:1 at the midpoint of operating interest, and most well made internal tuners can manage the band edges in that case — when the load is non-resonant and presents a high SWR.

I suspect a real auto-tuner that can handle just about anything at 1500 watts at key down for a long period would take at least another KPA1500 sized box.

(Just another curmudgeonly opine)


Grant NQ5T
K3 #2091, KX3 #8342

> On Apr 21, 2017, at 2:57 PM, Wes Stewart <[hidden email]> wrote:
>
> Without modeling it, I would guess that it will actually narrow the matched BW and it makes it a single band antenna at the same time.
>
> My Drake L4-B would drive anything.  When I decided I needed a new challenge (9BDXCC) I wanted to get on 160.  Of course the Drake didn't cover 160 and my then K3, now K3S doesn't have a tuner.  So I added some wire to the ends of the 80-meter inverted V.  This meant that I didn't have an 80-meter antenna but the Drake would drive it anyway.  Currently, with a KPA500 and KAT500 I have modest power on 160 but the KAT500 chokes on 80 at above 200-300 Watts.
>
> Hence the new vertical for next season.
>
> On 4/21/2017 11:10 AM, [hidden email] <mailto:[hidden email]> wrote:
>> It is very easy to put a hairpin coil on your top band vertical and
>> bring the resonant SWR to 1:1. This should give you much more usable
>> SWR bandwidth for the KPA1500. Many commercial tube amplifiers will
>> only tolerate 2:1 SWR.
>>
>> John KK9A
>>
>>
>>

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[Vic Rosenthal]

Just as a bit of anecdotal data, I am feeding a 20m dipole with 1200 watts through 600-ohm open line on 40 through 10 meters. The SWR on 40 meters approaches 100:1 (the line is short, but I am still eating about 2.2 dB loss).

Anyway, this presents a very difficult problem for most tuners -- and if you try it with an unbalanced tuner plus balun, even a 5kW DXE balun gets too hot quickly.

My solution was to cancel the reactance by switching in external capacitance or inductance as needed on 'difficult' bands (40 and 30 meters) and then letting a commercial autotuner take it from there.

Some day I'll put the matching circuits at the antenna and get the 2.2 dB back.

Vic 4X6GP

> On 21 Apr 2017, at 22:59, GRANT YOUNGMAN <[hidden email]> wrote:
>
> 2.  There are many ways to bring any antenna/feedline's Z0 to something that a reasonably-sized affordable auto-tuner can handle at not too great a feed line SWR.  Not the least of which is to feed a commercial old fashioned mechanical tuner with heavy-rated components that can handle the reflected power from whatever bobbie-pin you’re trying to match without just melting all the plastic in the tuner if you key down for a bit too long.
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