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Bob McGraw - K4TAX

Re: KPA500

I'll pass on linear supplies. Too heavy, too inefficient.

73
Bob, K4TAX

----- Original Message -----
From: "Doug Faunt N6TQS +1-510-655-8604" <[hidden email]>
To: <[hidden email]>
Cc: <[hidden email]>; <[hidden email]>; <[hidden email]>
Sent: Sunday, April 18, 2010 4:56 PM
Subject: Re: [Elecraft] KPA500

> It's not a switcher. As is common for linear power supplies (and not
> uncommon for switchers), there's an input voltage selector as part of
> the input power connector/fuse/switch combo.
>
> Since the power transformer is 15 of the 22 pounds weight, one of my
> thoughts was to ship that part (or an extra) ahead when traveling, and
> when I asked was told that currently it takes about 15 minutes to
> install, but that time might be cut.
>
> 73, doug
>
> From: "Bob McGraw - K4TAX" <[hidden email]>
> Date: Sun, 18 Apr 2010 16:24:43 -0500
>
> Any switching supply today and one that's "worth it's salt" should
> operate
> satisfactorily from 100 VAC to 250 VAC. So 120 VAC or 230VAC should
> not be
> of conern.
>
> 73
> Bob, K4TAX
>
>
> ----- Original Message -----
> From: "Don Wilhelm" <[hidden email]>
> To: "David Ferrington, M0XDF" <[hidden email]>
> Cc: <[hidden email]>
> Sent: Friday, April 16, 2010 3:40 PM
> Subject: Re: [Elecraft] KPA500
>
> > David,
> >
> > Because not all have hamshacks that are wired for 220 volts. If the
> > space was not wired specifically for hamshack use, there is likely to
> be
> > only 120 volt receptacles available. Up to 1000 watts draw (500
> watts
> > with 50% efficiency) on a normal 120 volt 15 amp circuit is practical,
> > but attempting to run more than becomes marginal.
> >
> > 73,
> > Don W3FPR
> >
> > David Ferrington, M0XDF wrote:
> >> I'm intrigued, obviously we'd look for 220v over here, but why not
> 120v
> >> in US?
> >> 73 de M0XDF, K3 #174
>

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Doug Faunt N6TQS +1-510-655-8604

Re: KPA500

See my earlier note as to one reason it was chosen. Elecraft learned from
the K2 about being a good player in a multi-TX environment (which can
just be neighbors).
Also, the 60V supply is providing no current when key up, and needs to
go to full output on key down- apparently this is less of a problem
with a linear supply than with a switcher. And of particular
significance to CW ops.

BTW, much of what I'm writing is my repeating what I was told or heard,
and none of it is binding on Elecraft, and is subject to my
misinterpretation, as well as changes down the line. The amp is still
in prototype, and has lots of testing to endure before it's solid.

I trusted them two years ago (i have K3 #22) and I trust them now.

73, doug

From: "Bob McGraw - K4TAX" <[hidden email]>
Date: Sun, 18 Apr 2010 17:02:04 -0500

I'll pass on linear supplies. Too heavy, too inefficient.

73
Bob, K4TAX

----- Original Message -----
From: "Doug Faunt N6TQS +1-510-655-8604" <[hidden email]>
To: <[hidden email]>
Cc: <[hidden email]>; <[hidden email]>; <[hidden email]>
Sent: Sunday, April 18, 2010 4:56 PM
Subject: Re: [Elecraft] KPA500

> It's not a switcher. As is common for linear power supplies (and not
> uncommon for switchers), there's an input voltage selector as part of
> the input power connector/fuse/switch combo.
>
> Since the power transformer is 15 of the 22 pounds weight, one of my
> thoughts was to ship that part (or an extra) ahead when traveling, and
> when I asked was told that currently it takes about 15 minutes to
> install, but that time might be cut.
>
> 73, doug
>
> From: "Bob McGraw - K4TAX" <[hidden email]>
> Date: Sun, 18 Apr 2010 16:24:43 -0500
>
> Any switching supply today and one that's "worth it's salt" should
> operate
> satisfactorily from 100 VAC to 250 VAC. So 120 VAC or 230VAC should
> not be
> of conern.
>
> 73
> Bob, K4TAX
>
>
> ----- Original Message -----
> From: "Don Wilhelm" <[hidden email]>
> To: "David Ferrington, M0XDF" <[hidden email]>
> Cc: <[hidden email]>
> Sent: Friday, April 16, 2010 3:40 PM
> Subject: Re: [Elecraft] KPA500
>
> > David,
> >
> > Because not all have hamshacks that are wired for 220 volts. If the
> > space was not wired specifically for hamshack use, there is likely to
> be
> > only 120 volt receptacles available. Up to 1000 watts draw (500
> watts
> > with 50% efficiency) on a normal 120 volt 15 amp circuit is practical,
> > but attempting to run more than becomes marginal.
> >
> > 73,
> > Don W3FPR
> >
> > David Ferrington, M0XDF wrote:
> >> I'm intrigued, obviously we'd look for 220v over here, but why not
> 120v
> >> in US?
> >> 73 de M0XDF, K3 #174
>

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W8JI

Re: KPA500 active devices!!

In reply to this post by Guy, K2AV

It's pretty basic stuff Guy.

Look at what happens in this MRF150:

http://www.w8ji.com/demonstation.htm

It would be nice if there was a free lunch and we could
magically buy a device that didn't care about the load and
gave reasonable operating efficiency and good IMD with any
impedance from perfect to a 3:1 mismatch, but it isn't
possible. Not blowing up in a few seconds on a data sheet
test circuit is a whole lot different than being acceptable
to operate that way in the real world.

73 Tom

<<<<<
Device web site was claiming "any angle" in the device
specs.
(!!!???) This should be fun to watch.

73, Guy.

On Sun, Apr 18, 2010 at 9:54 AM, Matt Palmer
<[hidden email]> wrote:

> Well said tom, an often overlooked aspect is the angle of
> the
> mismatch, load pull is the only way to tell, while a 3:1
> resitive is
> not to harsh, very few things will survive a 3:1 at an
> inductive
> reactance angle. Load pull is the only way to be sure, and
> I would be
> uncomfortable making any claims until such a test has been
> done.
>
>
> Matt
> W8ESE
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Bill Coleman-2

Re: KPA500

In reply to this post by Don Wilhelm-4

On Apr 16, 2010, at 4:40 PM, Don Wilhelm wrote:

> Because not all have hamshacks that are wired for 220 volts. If the
> space was not wired specifically for hamshack use, there is likely to be
> only 120 volt receptacles available. Up to 1000 watts draw (500 watts
> with 50% efficiency) on a normal 120 volt 15 amp circuit is practical,
> but attempting to run more than becomes marginal.

1000 watts is only 8 1/3 amps on a circuit that can handle 15. And why max out at 15 amps? My house was built in 1994, and has 20 amp circuits and wiring throughout. 15 amps is likely only the limit of the plug. I have successfully run my camping trailer's air conditioner off one of these outlets. I've measured it at 1400 watts draw at about 12 amps.

There are hair dryers that draw more current than this. At 1500 watt draw is not unreasonable from a 120v outlet.

Ironically, the only 15 amp circuit in my house is on the 240 volt outlet for my current amplifier.

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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Eric Swartz - WA6HHQ

Re: KPA500 active devices!!

Administrator

In reply to this post by Joe Subich, W4TV-4

The fcc requires amplifier gain to be 15 decibels maximum for any amatuer radio amplifier.

In reality, with negative feedback applied to level PA gain, the required drive to reach 500W is closer to 30 W here.
Eric
_..._

"Joe Subich, W4TV" <[hidden email]> wrote:

>
>The VRF2933 is rated for 300 Watts each according to the data
>sheet on the manufacturer's web site (Microsemi) ... That makes
>their use in a 500 W amplifier reasonable from an IMD perspective.
>
>The VRF 2933 minimum gain is also 20dB (23 dB typical) so it
>would appear that the KPA-500 should be capable of clean
>operation with 5 W of drive (e.g., K3 in low power mode).
>
>73,
>
> ... Joe, W4TV
>
>
>
>
>> -----Original Message-----
>> From: [hidden email]
>> [mailto:[hidden email]] On Behalf Of Doug
>> Faunt N6TQS +1-510-655-8604
>> Sent: Saturday, April 17, 2010 6:45 PM
>> To: [hidden email]
>> Subject: [Elecraft] KPA500 active devices!!
>>
>>
>> There are two VRF2933's in push-pull, so they're not 750
>> watts each, but per pair. There are only three amps in
>> existance, and no devices have been destroyed (yet). Again,
>> 500 watts is a very conservative rating. It's been key-down
>> for 10 minutes withy no problems.
>>
>> 73, doug
>
>
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Garry Shapiro

Re: News from Visalia! (:-))

In reply to this post by Ken Kopp-3

Actually, a linear power supply, not a switcher.

Garry, NI6T

On 4/16/2010 11:07 AM, Ken Kopp wrote:

> Hello from Visalia, where the doors haven't opened yet.
>
> Of course the P3 is waiting for the crowd to gather in front
> of the Elecraft booth. Rose has already measured it for a
> cover. (:-)
>
> Of perhaps as much interest is the new KPA500 amplifier
> that's just appeared on the table. All I can tell you is that
> it's somewhat weighty and has a switching supply built
> into the cabinet. The cabinet is the same size as a K3,
> so Rose won't need to design a new cover.
>
> I really don't know much more ... stay tuned.
>
> 73! Ken Kopp - K0PP
> [hidden email]
> http://tinyurl.com/7lm3m5
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>

Alan Bloom

Re: KPA500

In reply to this post by Bob McGraw - K4TAX

I think I overheard at Visalia that the KPA500 draws only 1 kW from the
AC power line with 500W out. It uses a high-efficiency toroidal power
transformer. I doubt that a switching power supply would do any better
than that.

The total weight is about 22 pounds I believe. Less than many
transceivers.

Al N1AL

On Sun, 2010-04-18 at 17:02 -0500, Bob McGraw - K4TAX wrote:

> I'll pass on linear supplies. Too heavy, too inefficient.
>
> 73
> Bob, K4TAX
>
>
>
> ----- Original Message -----
> From: "Doug Faunt N6TQS +1-510-655-8604" <[hidden email]>
> To: <[hidden email]>
> Cc: <[hidden email]>; <[hidden email]>; <[hidden email]>
> Sent: Sunday, April 18, 2010 4:56 PM
> Subject: Re: [Elecraft] KPA500
>
>
> > It's not a switcher. As is common for linear power supplies (and not
> > uncommon for switchers), there's an input voltage selector as part of
> > the input power connector/fuse/switch combo.
> >
> > Since the power transformer is 15 of the 22 pounds weight, one of my
> > thoughts was to ship that part (or an extra) ahead when traveling, and
> > when I asked was told that currently it takes about 15 minutes to
> > install, but that time might be cut.
> >
> > 73, doug
> >
> > From: "Bob McGraw - K4TAX" <[hidden email]>
> > Date: Sun, 18 Apr 2010 16:24:43 -0500
> >
> > Any switching supply today and one that's "worth it's salt" should
> > operate
> > satisfactorily from 100 VAC to 250 VAC. So 120 VAC or 230VAC should
> > not be
> > of conern.
> >
> > 73
> > Bob, K4TAX
> >
> >
> > ----- Original Message -----
> > From: "Don Wilhelm" <[hidden email]>
> > To: "David Ferrington, M0XDF" <[hidden email]>
> > Cc: <[hidden email]>
> > Sent: Friday, April 16, 2010 3:40 PM
> > Subject: Re: [Elecraft] KPA500
> >
> > > David,
> > >
> > > Because not all have hamshacks that are wired for 220 volts. If the
> > > space was not wired specifically for hamshack use, there is likely to
> > be
> > > only 120 volt receptacles available. Up to 1000 watts draw (500
> > watts
> > > with 50% efficiency) on a normal 120 volt 15 amp circuit is practical,
> > > but attempting to run more than becomes marginal.
> > >
> > > 73,
> > > Don W3FPR
> > >
> > > David Ferrington, M0XDF wrote:
> > >> I'm intrigued, obviously we'd look for 220v over here, but why not
> > 120v
> > >> in US?
> > >> 73 de M0XDF, K3 #174
> >
>
>
> ______________________________________________________________
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Matt Palmer-4

Re: KPA500

Switching supply can do much better than 50% efficiency, I've designed
several for use in PA's that are close to 95% efficient. The
dominating inefficiency is usually in the PA

Matt
W8ESE
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Jerry T. Dowell

Re: KPA500

In reply to this post by Bob McGraw - K4TAX

And too quiet!

It would not be advisable to operate a linear supply in close proximity to
the K3 or the K2. The resulting unwanted modulations have been discussed
previously.

Jerry AI6L

-----Original Message-----
From: Bob McGraw - K4TAX [mailto:[hidden email]]
Sent: Sunday, April 18, 2010 3:02 PM
To: Doug Faunt N6TQS +1-510-655-8604
Cc: [hidden email]; [hidden email]; [hidden email]
Subject: Re: [Elecraft] KPA500

I'll pass on linear supplies. Too heavy, too inefficient.

73
Bob, K4TAX

----- Original Message -----
From: "Doug Faunt N6TQS +1-510-655-8604" <[hidden email]>
To: <[hidden email]>
Cc: <[hidden email]>; <[hidden email]>; <[hidden email]>
Sent: Sunday, April 18, 2010 4:56 PM
Subject: Re: [Elecraft] KPA500

Jim Brown-10

Power Outlets for Ham Shacks

In reply to this post by Bill Coleman-2

On Sun, 18 Apr 2010 19:00:26 -0400, Bill Coleman wrote:

>There are hair dryers that draw more current than this. At 1500 watt draw is
>not unreasonable from a 120v outlet.

Yes and no. The current drawn by power supplies is NOT sinusoidal, it is a
series of pulses at the positive and negative peaks of the 60 Hz sine wave to
recharge the input filter capacitor. This causes the voltage drop in the
wiring between the breaker panel and the outlet to be greater than would be
predicted by Ohm's Law for a sine wave. This is true regardless of whether
the power supply is a linear supply or a switching supply.

In today's world, it makes good sense to over-size the conductors that feed
ANY outlet, especially one that is likely to be heavily loaded. NEC (US
electrical code) requires AT LEAST AWG #14 for a 15A outlet and #12 for a 20A
outlet (and larger if the run to the outlet is long). Most of the cost of
installing an outlet is labor. If you're going to add an outlet to your ham
shack, I'd run #10 conductors (to reduce the voltage drop) and install a 20A
breaker.

Another point. Common neutrals should be avoided. That is, it is always best
to run individual phase (hot) and neutral conductors to each outlet.

You can read more about pulsed currents and the problems they cause in the
Power and Grounding White Paper that's on my website.

http://audiosystemsgroup.com/publish.htm

73,

Jim Brown K9YC

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Vic K2VCO

Re: KPA500

In reply to this post by Jerry T. Dowell

On 4/19/2010 9:05 AM, Jerry T. Dowell wrote:
> And too quiet!
>
> It would not be advisable to operate a linear supply in close proximity to
> the K3 or the K2. The resulting unwanted modulations have been discussed
> previously.

Obviously I haven't tried it (!) but I suspect that the external magnetic field from a
toroidal transformer is much less extensive than that of the usual laminated type.
--
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco/
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Joe Planisky

Re: KPA500

In reply to this post by Jerry T. Dowell

I don't understand the "too quiet" comment, if it's intended to be
serious.

As for the "unwanted modulations", that's probably why they've chosen
a toroidal power transformer.

73
--
Joe KB8AP

On Apr 19, 2010, at 9:05 AM, Jerry T. Dowell wrote:

> And too quiet!
>
> It would not be advisable to operate a linear supply in close
> proximity to
> the K3 or the K2. The resulting unwanted modulations have been
> discussed
> previously.
>
> Jerry AI6L
>
> -----Original Message-----
> From: Bob McGraw - K4TAX [mailto:[hidden email]]
> Sent: Sunday, April 18, 2010 3:02 PM
> To: Doug Faunt N6TQS +1-510-655-8604
> Cc: [hidden email]; [hidden email]; [hidden email]
> Subject: Re: [Elecraft] KPA500
>
> I'll pass on linear supplies. Too heavy, too inefficient.
>
> 73
> Bob, K4TAX

W8JI

Re: KPA500

In reply to this post by Vic K2VCO

Don't bet on it. :-)

<<
----- Original Message -----
From: "Vic K2VCO" <[hidden email]>
Obviously I haven't tried it (!) but I suspect that the
external magnetic field from a
toroidal transformer is much less extensive than that of the
usual laminated type.
>>

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Joe Planisky

Re: KPA500

Hi Tom,

Please expand on your comment. I had the same thought as Vic. Why
wouldn't a toroidal power transformer have less magnetic field
coupling to external circuits than a conventional E/I core transformer?

73
--
Joe KB8AP

On Apr 19, 2010, at 5:38 PM, Tom W8JI wrote:

> Don't bet on it. :-)
>
>
> <<
> ----- Original Message -----
> From: "Vic K2VCO" <[hidden email]>
> Obviously I haven't tried it (!) but I suspect that the
> external magnetic field from a
> toroidal transformer is much less extensive than that of the
> usual laminated type.
>>>
>

gm3sek

Re: KPA500

In reply to this post by W8JI

>From: "Vic K2VCO" <[hidden email]>
>Obviously I haven't tried it (!) but I suspect that the
>external magnetic field from a
>toroidal transformer is much less extensive than that of the
>usual laminated type.

Tom W8JI wrote:
>Don't bet on it. :-)
>

Tom and I discussed this on the AMPS reflector, back in 2007. Flux
leakage from a toroidal winding at 50/60Hz is MUCH less of a concern
than it is with toroids at RF.

The specific question on AMPS was whether two toroidal transformers can
be stacked closely together without magnetic interaction, and the answer
was: Yes, they can. With two identical toroidal transformers sitting one
on top of the other, I connected 230V AC to the primary of one and
measured only a few millivolts on the open-circuit primary of the other.

That isn't quite the same topic as the flux leakage from a single large
transformer, but it's a good indication that leakage can be very low
indeed.

Obviously the answer will also depend on the quality of design and
construction, not only in the transformer but also in the rest of the
amplifier, because flux leakage is also affected by the external
connecting wires. For the lowest possible flux leakage, it is important
to minimize the physical size of the 'coupling loops' created by the
connecting wires, especially if the stray magnetic fields can also
interact with a steel chassis.

--

73 from Ian GM3SEK
http://www.ifwtech.co.uk/g3sek
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W8JI

Re: KPA500` (flux leakage)

Some years ago I received a complaint from W4ZV about
spurious signals offset about 1 kHz or so on my Icom 751A.
There was no amplitude modulation of the carrier visible on
scope, yet Bill could easily hear the spurs.

It turned out the toroidal transformer in the 751A internal
power supply had enough flux leakage to change the reactance
of the VCO coils that were about 3 inches from the toroid.
The rig was being FM modulated. I rotated the power supply
90 or 180 degrees and the problem went away.

At radio frequencies using a red "-2" mix, there can be
almost 30% change in inductance from spreading or bunching
turns in a coil. This is from core flux leakage. I've had
low pass filters put ripples in an adjacent filter when the
toroids get too close. These cores are largely touted as
"self-shielding" in our handbooks.

I'd be very careful accepting broad general statements
without looking at the specific case in question.

73 Tom

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AD6XY

Re: KPA500 active devices!!

In reply to this post by Eric Swartz - WA6HHQ

"The fcc requires amplifier gain to be 15 decibels maximum for any amatuer radio amplifier. "

What a stupid regulation! On the one hand you are allowed 1500W and on the other only 15dB gain? It makes no sense. Presumably one of the CB regulations.

A gain of 15 dB is reasonable for a single stage FET amplifier I agree. Does the FCC also forbid operating amplifiers in series?

Mike

Jim Brown-10

Leakage Flux from Toroidal Transformer

In reply to this post by gm3sek

On Tue, 20 Apr 2010 07:22:33 +0100, Ian White GM3SEK wrote:

>Obviously the answer will also depend on the quality of design and
>construction, not only in the transformer but also in the rest of the
>amplifier, because flux leakage is also affected by the external
>connecting wires. For the lowest possible flux leakage, it is important
>to minimize the physical size of the 'coupling loops' created by the
>connecting wires, especially if the stray magnetic fields can also
>interact with a steel chassis.

I never bothered to figure out why, but the first family of Crown audio
power amps that used toroidal power transformers had BODACIOUS levels of
leakage flux that could drive you NUTS in a live situation, when they
coupled into line level audio circuits. We had to solve that by physically
rotating them.

73,

Jim K9YC

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Mike WA8BXN

Re: KPA500

In reply to this post by Joe Planisky

Isn't the I-E stack of a conventional power transformer just a rectangular
binocular core made out of steel?

Now, if you are comparing an air wound coil to a toroid, there will be a big
difference in terms of radiation to surrounding areas.

73 - Mike WA8BXN

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W8JI

Re: KPA500

> Isn't the I-E stack of a conventional power transformer
> just a rectangular
> binocular core made out of steel?

Almost. It is impossible to grain orient the entire core,
and there are core areas out near the corners that have very
little flux but add weight and cost. Rounder cores are
nicer.

The performance difference depends on the particular core,
how the core is configured or stacked, how conductors are
arranged, and where and how we are measuring the flux.

In an E-I lamination the normal stacking procedure is to
alternate single or groups of laminations. E from one
winding end, then E from the other end. The result of this
is much less air gap because I's are sandwiched between E's
at both ends. The result is very little air gap in the flux
path. The more the manufacturer interleaves the E's and I's,
the less flux leakage there is.

Chokes on the other hand are generally made with the E's all
from one side, and a little paper spacing all the I's from
the E's. This makes an intentional air gap. The gap reduces
tendency to saturate, and can actually increase inductance
when dc current is present. It also causes very high levels
of flux leakage. Boy Scouts within miles of a typical filter
choke can no longer rely on their compasses.

Toroids are not perfect. Over half of the wire in the
winding is outside the window. Outside the hole, that wire
adds a lot of resistance compared to the inductance! This is
where the dual C core transformers come in. With a thick
core, most of the copper is inside the window. Pound for
pound and physical volume for physical volume, they have the
best ESR performance. They are really nothing more than two
toroids side by side with a common winding sharing both
cores.

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