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time for KPA1500 - but why "no tubes?"

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DOUGLAS ZWIEBEL

time for KPA1500 - but why "no tubes?"

RE: memo below.

Excuse me, but there were (are?) lots of "no tune" rigs that use
tubes. I used one (an Alpha 78) over 25 years ago. Of course, since
then, I've been a QRPer, so moot point for me.

de Doug KR2Q

>Yes, it *has* to be solid state. It would be complete insanity for Elecraft

Agreed - a new tube design would be moving in the opposite direction on
the technological timeline.

I operated the ARRL DX contest with K3/AL80BQ (QSK). Bandhopping was
slowed by the need to tune the amp each time
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Hank Garretson

Re: time for KPA1500 - but why "no tubes?"

On Mon, Feb 20, 2012 at 8:18 PM, Ron D'Eau Claire <[hidden email]> wrote:

Note that "No Tune" means, simply, "Fixed Tuned", set for a 50 ohm
> non-reactive load on each band. If we don't have an antenna reasonably flat
> across the whole band we add an "Antenna Tuner" to the output which is
> simply moving the tuning we used to do on the xmtr output to an outboard
> box!
>

Not exactly. My "No Tune" ACOM 2000A will automatically handle up to 3:1
SWR on all bands except 160 where the limit is 2:1. Sometimes output power
is reduced, and sometimes an external tuner is helpful. but for the ACOM at
least, "No Tune" does not mean "Fixed Tune."

73,

Hank, W6SX

Mammoth Lakes, California

Elevation 8083 feet in John Muir's Range of Light
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Don Wilhelm-4

Re: time for KPA1500 - but why "no tubes?"

WOW, I do not understand the distinction - there must be some harmonic
suppression circuits that reduce the 2nd harmonic emissions from an
amplifier (40 dBc if I recall), so whether that is done using a fixed
tune output circuit, or whether that is achieved by the use of an
external antenna tuner is a moot point. The bottom line is that
somewhere in the path between the PA tubes (transistors, MOSFETs), there
must be a path from the grid(, base, plate) to ground that will afford a
transition to 50 ohms (and X - j0) solution that will yield greater than
5 watts on all bands (or in the case of the K3, 6 meters).

So use whatever tuner matching section between the amplifier and the
antenna is a good and prudent challenge. The inductance at the highest
frequency will be greater than 3 times the 'oscilloscope oscilloscope
and probe -

73,
Don W3FPR

On 2/20/2012 11:34 PM, Hank Garretson wrote:

> On Mon, Feb 20, 2012 at 8:18 PM, Ron D'Eau Claire<[hidden email]> wrote:
>
> Note that "No Tune" means, simply, "Fixed Tuned", set for a 50 ohm
>> non-reactive load on each band. If we don't have an antenna reasonably flat
>> across the whole band we add an "Antenna Tuner" to the output which is
>> simply moving the tuning we used to do on the xmtr output to an outboard
>> box!
>>
> Not exactly. My "No Tune" ACOM 2000A will automatically handle up to 3:1
> SWR on all bands except 160 where the limit is 2:1. Sometimes output power
> is reduced, and sometimes an external tuner is helpful. but for the ACOM at
> least, "No Tune" does not mean "Fixed Tune."
>
> 73,
>
> Hank, W6SX
>
> Mammoth Lakes, California
>
> Elevation 8083 feet in John Muir's Range of Light
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>

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David Gilbert

Re: time for KPA1500 - but why "no tubes?"

In reply to this post by Hank Garretson

i don't know how you get the idea that it isn't fixed tune. Just
because it can handle a 3:1 SWR without self-destructing does not mean
it isn't fixed tune. What tuning parameters do you think are changing?

Dave AB7E

On 2/20/2012 9:34 PM, Hank Garretson wrote:

Mike Harris

Re: time for KPA1500 - but why "no tubes?"

In reply to this post by Don Wilhelm-4

Quite a few years ago I was running the comm's on one of the British
Antarctic Survey bases (Adelaide Is). My main TX used a Racal amp with
3 x 4-400 in parallel (if I remember correctly). It used a Pi-L
network. That network quite happily matched 20:1 SWR if necessary. The
tuning was rather critical but in other respects all was normal as far
as the tubes were concerned. The coax (RG-8 type) from the TX to the
balun would run very warm in those circumstances and sag from the ceiling.

Not desirable I admit but necessary to broadcast safety critical WX
forecasts to remote sledging teams on a frequency in the 2MHz range that
the antenna was never designed for and seldom used.

Regards,

Mike VP8NO

On 21/02/2012 04:14, Ron D'Eau Claire wrote:

> Well, Don, it's been a number of years since I homebrewed an amp, but from
> what I recall a pi-net wouldn't meet the later FCC regs and a Pi-L network
> only sufficed over a fairly narrow matching range.
>
> By the 1970's I was counting on my outboard "antenna tuner" that matched my
> open wire feeders to provide the added spur suppression to meet FCC regs
> even though I was still using a tunable Pi-L network on the output of my
> homebrew rig.
>
> 73, Ron AC7AC

Ignacy

Re: time for KPA1500 - but why "no tubes?"

For CW, this might be easy. A single MRFE6VP61K25H is used now commercially for 2m: 2 W in 1 KW out. This is key down not pulse mode; see http://www.w6pql.com/parts_i_can_provide.htm

Since W6PQL offers it for sale, he must have done lots of testing and determined good reliability.

In CW, KPA500 with such a device perhaps could provide 800-900W due to increased efficiency (70 vs 45%). Two such modified KPA500 would easily make 1.5 KW on CW. Also can be driven by K3/10.

SSB would be a different question. But Elecraft is innovative. Why not class B be with forward correction....

Ignacy, NO9E