[Elecraft] Re: More Quests: Driving (big) linear amps with the K2?

[Brian Murphy]

Hello Peter,

First the K2 issue.

Mine is #204.  I just missed the field trial 100!  Prior to the K2 I have
used the TS520, TS820, and an old ship-to-shore HF.  I used a R390A for
years, but now have a RACAL 6790.  I also have a 40m SST (now this is a neat
radio!!!  Only 17 mA for receive and very narrow filters).

The K2 was a great jump in technology from the Kenwoods.  I strongly
recommend it.  It is probably the best radio for the money anywhere. It is
my primary rig.  Building it is not trivial, though.  There must be a
thousand parts.  The good part is that with the support you can get from
Elecraft, you have a very high probability of finishing with an excellent
radio.  This is THE key point--the risk of not getting a fine radio at the
end of the process is very low, indeed.

Over the last few years, I have added the tuner, internal battery (a
dynamite combination for operating class "BY" (BackYard mobile) under the
stars with a wire thrown over the oak tree branch above my deck).  I also
added the 160m and SSB.  All work fine and no problems with my SSB audio,
either with PSK31 or with voice on either sideband on any band.  More
recently, I ordered the NB since electric fences are a problem at my new
QTH.  To sum it up, there is little to no risk of disappointment with the
K2.  Just do not get into a hurry--if you feel rushed, then stop immediately
and take a break.

Now for the QRO issue.

Like you, I could not see paying 3K+ for high power every now and then,
although the 11 year cycle will make an amp more useful for the next few
years.  Since I am new to the QRO (1KW + arena), I may not be the best
source for information on those issues.  With that caveat, here is my
experience so far.

I have used a horizontal loop at 100W fed by real open wire line and was
very pleased with its operation.  I have to agree with the recent QST
article about horizontal loops--they are underrated!  Wire antennas are
cheap if you have some trees at strategic locations near your shack.  And,
it sure beats burying radials.  Before I put 1KW on a horizontal loop, I
will have to do the rf radiation review now required by the FCC.  There is
an easy calculation for dipoles, though.

I have used a GAP vertical without radials (the Voyager had 3 counterpoises)
with fairly good results.  In that QTH I had no suitable trees, though.

Most of the 500 watt + amps need 220vac, but some can also run on 110v at
reduced power.  Again, I feel that if I am going to the trouble and expense,
then why not go for at least 1200-1500watts.

Now, as you may have gathered, I am perfectly comfortable with experimenting
with antennas, transmission lines, amps, and radios that are non-mainstream.
So, the Harris solution was attractive to me.  I am a little jittery about
putting my fingers around a high power, high voltage power supply, though.
Thus, I would rather buy an amp rather than build one.  Also, amplifying
from 5 watts to 1300 watts takes some real tricks to isolate the input from
the output so feedback will not occur.

Try the internet search for Harris and RF110.  Just remember that the power
supply is separate from the amp.  Fair Radio sells them for about $1400
without the power supply.  The power supply should run $200-$300 or maybe
less.  The amp has a two stage, 4 tetrode tube configuration and is
conservatively designed.  So the power supply must supply both plate and
screen supply voltages for all 4 tubes plus control power, etc--it is not a
trivial power supply to make yourself.  One common power supply for the
Harris is a 3 phase 400 cycle unit that was apparently used on military
aircraft ( a lot of 400 cycle there).

The keying circuit from Elecraft website is nice, but I manually switch mine
on SSB so far.  It is a little more trouble, but did I mention that I am
remodeling my house!  I also have a remote bandswitch for the amp.  The
Harris amp is pretuned in about 20 bands from 2-30 MC so you do not have to
dip the plate as in the Kenwood radios and most tube amps.  The Harris amp
is milspec and well constructed and designed.  It has many safety features
so it will probably last longer than most Ham amps.

By the way, I used my K2 maritime mobile last year.  I sailed a 45 foot
sloop from Rhode Island to North Carolina and used the K2 for daily e-mail
position reports to the XYL.  It was fairly easy to contact people in the
mid-USA on 20m during the day via PSK31.  The K2/PSK31 combination is
nothing short of phenomenal!  I was amazed at what 5 watts and PSK31 could
do.

As you can see, I have had a good experience with my K2--no regrets
whatsoever.  QRP is always a fun challenge, but as I said earlier,
propagation has been good the last year or two.  Regarding the amp, it
certainly complicates your life and operation with many more considerations,
procedures, "super-sized" components, extra heat in the room, but the power
company will love you for using it.  100 watts is a good compromise that
will work most times; 5-10 watts is not always so lucky.  It is much easier
to have the 100 watts available when needed and go read a good book when
that is not enough.  At around $350 for the 100 watt amp from Elecraft, this
is hard to beat.  But then again, did I say I loved challenges?

Good luck on your choice.  Let me know what you decide.  The main thing is
to have fun doing it safely and not to spend so much money that you cannot
recover it by selling the equipment later when your needs change.

Brian  N4YTL
_________________________________________________________

> From: "phoon.usinet" <phoon@attglobal.net>
> Date: Tue, 25 Jun 2002 20:54:29 -0600
> To: "Brian Murphy" <n4ytl@arrl.net>
> Subject: More Quests:   Driving (big) linear amps with the K2?
> 
> 
>> I had my eye on the QRO brand (I believe) amp with a single tetrode hoping
>> that I could easily modify the input circuitry of the amp to produce
>> 1000-1500 watts with only 5-10 watts from the stock K2.
> 
> I came close to buying a QRO Hf 2500DX QSK (beautiful amp, superb
> workmanship) but decided not to mainly because of the expense and hassle of
> getting a 220 volt AC line up to my bedroom.
> 
> An electrician estimated it at $300 for starters, and was still not sure the
> fuse box could take it.
> 
> Looked like fairly major re-wiring was involved.
> 
> Then he said it would be at least 6 to 8 weeks before he could get to it.
> 
> At that point, the whole thing was up to $3300 - $3700.  I've been QRP for
> years, and staggered under the sticker shock!  Do I really want to go QRO?
> 
> Maybe next summer after the dental bills are paid....
> 
> The other problem was I found that with 10 to 15 watts, from the K2,
> especially on 40 M, I would not be able to get the maximum power out from
> the HF 2500 for all my time and expense. I made exactly the same discovery
> you did, and hated the idea of cascading amps, first the K2 finals barefoot,
> then the KFA-100 to get to 40 or 50  watts, then the QRO HF 2500DX to get to
> 1500.  By the time I got this monstrosity on the air, how much distortion
> would all these amps add to SSB? Come on, hold it Peter, think, I said to
> myself!
> 
>> However, I came across a Harris RF110 amp for sale at less money than a
> used
>> QRO!  And, it required only 100 mW of drive (yes, that's milliwatts!).
> 
> Please tell me more about how and where you located this  Harris Amp that
> requires less drive.
> 
> Is the Harris 110 VAC or 220 VAC?
> 
> Did you build the amp keyer shown in the K2 website to key the Harris Amp?
> What other connections do you make to the amp?
> 
> What did you pay for yours?
>> 
>> I have not used it much
>> partly since propagation conditions have been so good, partly because it
> has
>> taken me some time to build a tuner, transmission lines, and antennas
> rated
>> for full power.
> 
> That is exactly where I am at Brian.  I have to design and build a 5/8 wave
> length vertical, lay some 72 radials in the soil, get RG 8U feed, wind my
> own loading coils.
> 
> This, to me, is a 2 month project.
> 
> I simply will not use an antenna that is not well designed and laid out.
> Vertical GPs work well more due to the wire on the ground, than the wire in
> the air.
> 
> I have a backpacking GP that works perfectly.
> 
> I couldn't see getting the linear until this was done.  And I still haven't
> even built a K2 yet.
> 
>> By the way,
>> there are apparently many RF 110s available, but the 220vac single phase
>> power supplies are the difficult component to find.
> 
> Don't these come with the amp?  Why so hard to find?
> 
> A question:  what antennas did you build that will handle the Harris output?
> 
> Do you think the Harris amp will cause RFI with fairly closeby neighbors?
> 
> I would think a good GP vertical, with lots of radials, will reduce the RFI
> problem.
> 
> Well, tell me all you can about the Harris amp.
> 
> Tell me about your K2 building experince.  I just heard on the reflector
> that the K2 SSB unit has poor audio on USB (or is it LSB).
> 
> Have you built the SSB unit?
> 
> Then this evening, I sat back, put my QRP+ on the air, 8W on 20, had S-9 CW
> in California with my tuned big wire loop, and said:   Why put myself
> through all this? Why bother building a K2, and worry about all these other
> shenanagens to get tot QRO?
> 
> All I really need is to build an amp keyer for my QRP+, and get a Harris
> someday.....
> 
> Comments, criticisms, disagreements, ideas, all welcomed.
> 
> Hope to hear from you,
> 
> Peter
> VE1CHS
> Lifetime Canadian Certificate
>