"Richard Clark" wrote
I SPECIFICALLY mandated a discussion of transistor
amateur amplifiers.
____________________

At least there appears to be an acknowledgement that some RF amplifiers do
not have a source impedance that is the conjugate of their load impedance.
So progress has been made.

RF

On Sun, 5 Sep 2004 11:51:57 -0500, "Richard Fry"
wrote:
appears to be

Hi OM,

Another punt.

73's
Richard Clark, KB7QHC

Richard Fry wrote:
"At least there appears to be an acknowledgement that some RF amplifiers
do not have a source impedance that is the conjugate of their load
impedance."

Those may be anomalous. I recommend King, Mimno, and Wing to anyone
desiring the complete story on the conjugate matches.

To the extent that the amplifier is designed for a performance on demand
that stresses it to its maximum safe dissipation, an amplifier of the
Class C variety is designed for a perfectly matched load. It`s the
economical thing to do.

You supply the tube with about all the volts it can safely take. Then
you supply it with just enough load impedance to limit its current to
all it can take under the heaviest loading it well encounter. That would
be when it is conjugately matched to a 50-ohm load, the usual cable
impedance specification.

The tank circuit is mostly a harmonic filter providing a very high
impedance to the fundamental frequency and shorting out the harmonics.

Best regards, Richard Harrison, KB5WZI

On Sun, 5 Sep 2004 12:47:45 -0500, (Richard
Harrison) wrote:

The tank circuit is mostly a harmonic filter providing a very high
impedance to the fundamental frequency and shorting out the harmonics.

Hi Richard,

Even here, the Goatman offered in his notes that his finals tank
(actually a series resonant Z match) offered a loaded Q of 2! (If I
read his scribblings correctly.)

73's
Richard Clark, KB7QHC

On Sun, 05 Sep 2004 18:06:07 GMT, Richard Clark
wrote:

|On Sun, 5 Sep 2004 12:47:45 -0500, (Richard
|Harrison) wrote:
|
|The tank circuit is mostly a harmonic filter providing a very high
|impedance to the fundamental frequency and shorting out the harmonics.
|
|Hi Richard,
|
|Even here, the Goatman offered in his notes that his finals tank
|(actually a series resonant Z match) offered a loaded Q of 2! (If I
|read his scribblings correctly.)

Yeah and he also calculates

(http://www.techatl.com/wrek/docs/gnm69_25.htm)

the required plate load resistance as:


Eb
Rl ~ -------
Idc

Which for class C is off by about a factor of 2, but with Eb = 2500
and Idc = .25, he does the division and comes up with Rl = 1000. Hey
what the heck, what's a factor of 10 among friends.

If the calculation is done more accurately:

Eb - Eg2
Rl = ---------
K * Idc

Where K = 2 for Class C and
Eg2 = 300 (screen voltage)

Then Rl ~ 4 Kohm

Since the minimum output capacitance (Cp) of a 4CX300 is 4.5 pF, the
parallel equivalent of Rl and Cp is Rp ~ 3920, Xp ~ -388.

Thus the minimum possible Q ~ 10, which to someone who has built a few
VHF amplifiers, sounds much more plausible.

For example here's one I designed and built not much later that the
WREK(ed) transmitter.

http://www.qsl.net/n7ws/K7CVT_Amp.html

But it gets worse. Try as I might with the component values he
specifies, I cannot develop a plate load Z anywhere close to what is
necessary. He has a lot more inductance that he thinks, so maybe that
helps and I suspect his output lowpass filter (seen in the photos but
not on the schematic) is part of the matching network.

I'm really surprised that with the construction and documentation
presented he could get FCC type acceptance.

On Tue, 07 Sep 2004 18:12:35 -0700, Wes Stewart
wrote:

He has a lot more inductance that he thinks, so maybe that
helps and I suspect his output lowpass filter (seen in the photos but
not on the schematic) is part of the matching network.

I'm really surprised that with the construction and documentation
presented he could get FCC type acceptance.

Hi Wes,

Still and all, a good story of the exploit.

Well given the measurements, it seemed some filtering was necessarily
unmentioned. And given the FCC type acceptance (obviously allowed),
the measurements (or rather the quality of the gear) were sufficient.
I especially find the scrawled notes submitted with the acceptance
application a time capsule back to the days before computers (or
seemingly the IBM selectric).

Still and all, he described where he was going, and offered how he
thought he got there. To translate that to today's specifications
"missing" the output Z of transmitters (obviously part and parcel to
the canon of the design engineer who built them) because of their
irrelevance - that is a stretch of imagination right off the showroom
floor. And then to notice in the ad copy, they can build to other
output Z's...

I find the novel modulation techniques interesting though. Seems like
an alphabet soup of modes has sprung up over the years.

73's
Richard Clark, KB7QHC

On Sun, 5 Sep 2004 12:47:45 -0500, (Richard Harrison)
wrote:

Richard Fry wrote:
"At least there appears to be an acknowledgement that some RF amplifiers
do not have a source impedance that is the conjugate of their load
impedance."

Those may be anomalous. I recommend King, Mimno, and Wing to anyone
desiring the complete story on the conjugate matches.

To the extent that the amplifier is designed for a performance on demand
that stresses it to its maximum safe dissipation, an amplifier of the
Class C variety is designed for a perfectly matched load. It`s the
economical thing to do.

You supply the tube with about all the volts it can safely take. Then
you supply it with just enough load impedance to limit its current to
all it can take under the heaviest loading it well encounter. That would
be when it is conjugately matched to a 50-ohm load, the usual cable
impedance specification.

The tank circuit is mostly a harmonic filter providing a very high
impedance to the fundamental frequency and shorting out the harmonics.

Best regards, Richard Harrison, KB5WZI

Gotta' disagree here, Richard, conjugate matching a Class C tube amp doesn't
require the heaviest loading it will encounter. A conjugate match can be
obtained with any loading you choose. For example, you can set the drive that
will permit loading to any particular level of maximum output power into any
load within the tank circuit's available matching range. So let's assume you set
the drive to provide a max output of 100 w into a 50-ohm load by adjusting the
tank controls for maximum output. The source resistance is now 50-ohms, there is
a conjugate match, and the amplifier has not been loaded to the heaviest
loading it will encounter. In addition, if the load was 70 ohms and the tank
adjusted for maximum output, the source resistance would now be 70 ohms, and
there'd also be a conjugate match.

If you question my statements above see the data from my measurements using
professional grade instruments in either QEX, May/Jun 2001, Chapter 19 in
Reflections II, or from my web page at http://home.iag.net/~w2du.

Walt

"Walter Maxwell" wrote
If you question my statements above see the data from my measurements
using
professional grade instruments in either QEX, May/Jun 2001, Chapter 19 in
Reflections II,

============================

The accuracy of measurements depends on who uses the instruments rather than
on what the manufacturer says in his sales catalogue. I'd much prefer just
to take your word for it, Walt. The manufacturer's type number is
superfluous - it sounds like a gratuitous advert.
----
Reg, G4FGQ

On Mon, 6 Sep 2004 10:01:15 +0000 (UTC), "Reg Edwards"
wrote:


"Walter Maxwell" wrote
If you question my statements above see the data from my measurements
using
professional grade instruments in either QEX, May/Jun 2001, Chapter 19 in
Reflections II,

============================

The accuracy of measurements depends on who uses the instruments rather than
on what the manufacturer says in his sales catalogue. I'd much prefer just
to take your word for it, Walt. The manufacturer's type number is
superfluous - it sounds like a gratuitous advert.
----
Reg, G4FGQ

Thanks for the compliment, Reg, that you prefer to take my word for it. However,
the reason we include the manufacturer is not as a gratuitutous advert, but to
distinguish between the Cadillacs (Hewlett-Packard and General Radio, among a
few others) and the non-descripts. The Cadillacs are professional, precision
instruments, which, when used by knowledgeable people, provide data that can be
relied upon.

Without knowledge of the quality of the measuring device the reader is
justifiably suspicious of the data.

Walt

On Mon, 06 Sep 2004 18:41:37 GMT, Walter Maxwell wrote:

[snip]
|Thanks for the compliment, Reg, that you prefer to take my word for it. However,
|the reason we include the manufacturer is not as a gratuitutous advert, but to
|distinguish between the Cadillacs (Hewlett-Packard and General Radio, among a
|few others) and the non-descripts. The Cadillacs are professional, precision
|instruments, which, when used by knowledgeable people, provide data that can be
|relied upon.
|
|Without knowledge of the quality of the measuring device the reader is
|justifiably suspicious of the data.

Careful Walt. Reg is an Englishman, he doesn't know what at Cadillac
is, other than an American automobile, which makes it suspect.

You should use Jaguar for comparison. Uh oh, better not, that is an
American company (Ford).

Alright, how about Aston Martin. Darn, another Ford.

I've got it; Rolls-Royce! Nope, that's a German car (BMW).

Okay maybe a Bentley. Nooo. That's a Volkswagon.

Surely a Land Rover. Not again! Another Ford.

You're right. HP and GR were the Cadillacs of the industry. [g]