Leland wrote:
(Twist the amp doesn't have to be class "C" to cause problems. Even a
class "B" linear amp is not completely clean. In particular solid state
amps are a problem because many are push-pull designs with no filtering
on the output.)

_
I take your word for it.
I mentioned the class only because of the myriad of posts condemning the
class C amps.
What is push-pull design?


_



(A push-pull design has low levels of even harmonic output since the
even order signals cancel out in the output transformer. And that is
only for "well matched" power transistors.)

_
I guess that sort of answers my previous question.....but is something
that is not well matched better than a push-pull design, or am I
thoroughly lost here?


_
( The problem with the push-pull design is the odd order harmonics are
not attenuated at all! If you care to look at Ham rigs that use wide
band solid state push-pull amplifier output for HF operation you will
see band pass filters on the output.)

_
Ahhhh,,,,that explains it.

_

( In fact these filters are switched in and out depending on the band in
use. That's how the manufactures keep the output clean enough to meet
FCC specifications.
Tube amplifiers are another story. These amplifiers can be relativity
clean IF the output is designed correctly. The critical section is the
output matching circuit. This circuit performs two important functions;
load matching and harmonic filtering. Some of the posters on this board
in the past don't seem to grasp these two ideas well. They seem to think
that if the amp loads up OK then all is well - not true. If you go
through the math you will discover that there is no unique solution for
the value of the matching section component values. So how do the
designers pick the values they do? They pick an operation "Q" for the
matching section, that forces a particular value for the components. The
significance of the "Q" value is it is a measure of how frequency
selective the matching section becomes. The higher the "Q" the sharper
the response becomes, thus the less harmonic energy is coupled to the
output. Pick a "Q" too low and you have significant harmonic output from
the amplifier. Pick a value too high makes the amplifier a pain to use,
in other words the amplifier has to be retuned for small shifts in
operating frequency. From either experience, or through detailed and
complex calculations, acceptable values for "Q" have been determined
that would yield a tube amplifier matching circuit that is likely to
have acceptably low levels of harmonic output content. )
_
Hell, someone should have solicited your opinion long ago on this
matter,,,so here goes.....what type low power tube amp (say 100 to 250
watts), if any, would you recommend for 10 meter?
_

(If somebody says their amp is "clean" well the only sure way to know is
to test it with a spectrum analyzer.)
_
Yea,,,,guess so. When I first used an amp, I asked my neighbors if they
heard so much as an errant erratic noise anywhere, to let me know. Years
ago I had a neighbor tell me she could hear me on a cordless phone or pc
speakers (can't remember which) and she declined any action on by behalf
to rectify the situation. I think she enjoyed listening. Nevertheless, I
made some changes because I thought that if she could hear me, them
others could, too. A tower and new antenna changed everything.


-

( If you look at reviews for Ham rigs, and power amplifiers in
particular, you will see spectrum analyzer screen shots so the buyers
can see for themselves just how clean the output happens to be. And I
haven't seen a spectrum analyzer screen shot for a 11m solid state
amplifier yet. If you know of any it would be interesting to see them. )

-

I don't. There is no question some of those high drive competition amps
are dirty as hell. While I would never use one for dx, I admit a
fondness for a shoot-out.


--
Leland C. Scott
KC8LDO
Wireless Network
Mobile computing
on the go