Solid state transmitters are notoriously finicky about matching to the
antenna. Tube equipment is not, so I am told, and early experience seems
to bear that out.

Certainly I can see one of my newer rigs start to fold back at 2:1.

What are the practical limitations of the Tube finals apparent
flexibility?

Is it safe to compare the load, plate, and drive controls to some of the
functions of a tuner? (possible real dumb question)

- 73 de Mike KB3EIA -

On Mar 4, 9:48?am, Mike Coslo wrote:
Solid state transmitters are notoriously finicky about matching to the
antenna. Tube equipment is not, so I am told, and early experience seems
to bear that out.

I disagree some with that, having entered HF radio comms
QSYing 1- to 15-KW transmitters. Failure to properly
neutralize a final RF amp can result in heating sufficient
to melt the glass envelope enough to let air in and thus
destroy the tube (an 833 that was mounted on the control
console at Army station ADA for weeks as a reminder).

Certainly I can see one of my newer rigs start to fold back at 2:1.

That's a somewhat arbitrary level that is designed into
most solid-state PAs. One can run them without the
VSWR sensing but it isn't a good idea.

For one thing, RF power transistors are expensive and
replacement is not the relatively easy task of just
unplugging the old tube and plugging in the new one.
It's a mechanical task and one has to remember to
properly heat-couple the new PA transistor...the amount
of waste heat is concentrated in a much smaller space
than big tube envelopes-bases.

What are the practical limitations of the Tube finals apparent
flexibility?

That's in many decades of old literature and covered
extensively. Data from commercial service transmitters
is more comprehensive than amateur types as a
general rule. Some of that may be hard to get now.

Is it safe to compare the load, plate, and drive controls to some of the
functions of a tuner? (possible real dumb question)

Not dumb, it's more like comparing potatoes and peas.

The long-common tube tuning controls are directly
connected to variable, relatively narrow-band tuning
and impedance-matching passive circuits. The tube
plate source impedance is relatively high compared
to the antenna feedline, even if that feedline is 600
Ohms balanced. The common pi-network is both
a resonating network and an impedance-changing
circuit.

An antenna tuner is very simlar to a tube pi-network
but operates either to change (narrowband) impedances
up or down relative to the feedline characteristic
impedance. Again, passive components do the work
of transformation.

By contrast, most of the solid-state power amplifiers
are broadband, much more so than common tube
circuits. Since their input-output impedances are
relatively low and known (and predictable) over a wide
frequency range, they can use broadband transformers
for matching. The end result in the design is one
without many of the tube controls' necessity.

Usually, but not always, either type of amplifier is
still suceptible to damage from mismatching load
impedances. The mismatching just takes on a
slightly different form between the two.

73,


Remember: All electronics works by smoke. If the smoke
gets out, it won't work... :-)

" wrote in
ups.com:

Failure to properly
neutralize a final RF amp can result in heating sufficient
to melt the glass envelope enough to let air in and thus
destroy the tube (an 833 that was mounted on the control
console at Army station ADA for weeks as a reminder).

I would also suspect that when dealing with 15 KW transmitters,
errors would be pretty unforgiving.


What are the practical limitations of the Tube finals apparent
flexibility?

That's in many decades of old literature and covered
extensively. Data from commercial service transmitters
is more comprehensive than amateur types as a
general rule. Some of that may be hard to get now.

I'm going to have to try to find some of the literature.



Remember: All electronics works by smoke. If the smoke
gets out, it won't work... :-)


Thanks much Len - I'm digesting the info now. I know it seems a
little strange to become interested in tube equipment at this late stage,
butour hobbies sometimes take us in strange directions. 8^)

- 73 de Mike KB3EIA -

On Mar 4, 3:56�pm, Mike Coslo wrote:
" wrote roups.com:

* *Failure to properly
* *neutralize a final RF amp can result in heating sufficient
* *to melt the glass envelope enough to let air in and thus
* *destroy the tube (an 833 that was mounted on the control
* *console at Army station ADA for weeks as a reminder).

* * * * I would also suspect that when dealing with 15 KW transmitters,
errors would be pretty unforgiving.

What are the practical limitations of the Tube finals apparent
flexibility?

* *That's in many decades of old literature and covered
* *extensively. *Data from commercial service transmitters
* *is more comprehensive than amateur types as a
* *general rule. *Some of that may be hard to get now.

* * * * I'm going to have to try to find some of the literature.

Besides old ARRL Handbooks prior to the 1970s, I'd suggest
finding the site that has digitized copies of GE Ham News.
Those were (bi-monthly?) hand-outs by GE to push their
tubes (naturally) but they contained lots of different ham
projects (using tubes, of course).

I found such a site a few years ago but didn't bookmark it.
Was incomplete then but being worked on. The 1960s
was a good peiod for new designs in USA amateur radio.
I used to grab my boss' copies as soon as he was done
with them back then. :-)

73, Len

" wrote in
oups.com:


Besides old ARRL Handbooks prior to the 1970s, I'd suggest
finding the site that has digitized copies of GE Ham News.
Those were (bi-monthly?) hand-outs by GE to push their
tubes (naturally) but they contained lots of different ham
projects (using tubes, of course).

Got it! Thanks a lot Len - I googled them up, and have enough reading
material to keep me busy for a while.

the site is: http://bama.sbc.edu/ge_ham_news.htm

- 73 de Mike KB3EIA -

From: Mike Coslo on Sun 4 Mar 2007 22:56

" wrote:

Besides old ARRL Handbooks prior to the 1970s, I'd suggest
finding the site that has digitized copies of GE Ham News.
Those were (bi-monthly?) hand-outs by GE to push their
tubes (naturally) but they contained lots of different ham
projects (using tubes, of course).

Got it! Thanks a lot Len - I googled them up, and have enough reading
material to keep me busy for a while.

the site is: http://bama.sbc.edu/ge_ham_news.htm

Thanks for the reminder on BAMA contents. BAMA has more
than just old tube equipment manuals. :-) Good site!

On the general subject of tube PA matching to load, some
remarks:

The automatic antenna tuner might have its beginning at
Collins Radio of the 1950s decade. Reference is the T-195
transmitter, part of a set that used the special version
of the R-390 series called the R-392, designed and built
for the USMC, first fielded in 1955, intended to be Jeep
mounted. The basic whip antenna matching was a servoed
single variable L and a single variable C to a conventional
PA output tank...so-called Ell-network, switchable to
the four possible L-C connection possibilities. On an
Army demo in late 1955, I was most impressed when the
demonstrating officer simply removed half of a whip
section (!), hit the tune function, and the servo
system re-tuned to this new antenna impedance in
seconds. :-)

Warren Bruene must have had a hand in that Autotune
labeled antenna matcher because it has the first instance
I've seen for the "Bruene detector" in the transmission
line to get both amplitude and phase of the RF. Slight
variations of that exist today, generally with a toroid
for current output and a small capacitor for voltage
output, both combined into dual diode detectors. Today's
antenna auto-tuning subsystems use binary-progression
switched single inductors and single capacitors with the
servo system basically a microcontroller plus small
frequency counter (sometimes) that can determine which
L or C to switch and remember the frequency and setting.
SGC (Stoner Goral Company) in the Puget Sound area of
Washington state has at least three models for both
maritime and amateur radio HF use. The Big3 (Icom,
Yaesu, Kenwood) have them, either built-in or as out-
board boxes. Several independent USA companies have
them.

ALL (no exceptions) antenna tuners have limits on
their impedance matching capabilities, whether "Pi-L"
output tanks or big boatanchor style structures
that look very impressive. There are few overall
advantages in any configuration with the possible
exception of Simplicity of the single L, single C
variety now common to today's autotuning matchers.
ALL, even the popular Pi-network, have limits that
can be proven mathematically; if the math doesn't
fit, no amount of publicity or historical references
will make it fit better.

If you or anyone else would like an algebraic-only
math explanation of the four combinations of single
L and C matching combinations...with their limits of
load impedance variation, I'll be happy to forward
them by e-mail attachments. No binary files here
and the equations, figures are better shown in the
PDF format.

73,

On Mar 4, 10:56 pm, Mike Coslo wrote:

the site is:http://bama.sbc.edu/ge_ham_news.htm

Mike,

If you like the BoatAnchor Manual Archive, you
may be interested in these sites. Lots of
downloadable manuals and data:

First is Pete Millett's book site:

http://www.pmillett.com/tecnical_books_online.htm

Has some incredible stuff, like complete ARRL and
Radio Handbooks, Radiotron Designer's Handbook,
Reference Data for Radio Engineers, and much more.
All in PDF.

CAUTION! Some files are quite large, and will take a long
time to download via dialup. One trick I have used is to set up
a dialup download late at night, hit the button and go to bed.

and tube data, from the RCA HB-3 books:

http://www.pmillett.com/hb-3_tube_manual.htm

arranged by inidvidual tube type, for easy download.


The Glowbugs website has lots of downloadable info:

http://www.mines.uidaho.edu/~glowbugs/index.html

including some good manuals and articles on WW2 military surplus:

http://www.mines.uidaho.edu/~glowbug...__Surplus.html

http://www.mines.uidaho.edu/~glowbugs/PDF%20files/

Some of these are quite large, too.


"Bunker of Doom" site with lots of stuff:

http://www.bunkerofdoom.com/

Tube manuals, for example.

Transformer catalogs and other data:

http://www.bunkerofdoom.com/xfm/index.html


Another good site:

http://www.antiqueradioarchives.com/archives_index.htm



73 de Jim, N2EY

On Mar 4, 12:48?pm, Mike Coslo wrote:
Solid state transmitters are notoriously finicky about matching to the
antenna. Tube equipment is not, so I am told, and early experience seems
to bear that out.

IMHO, it's really a matter of the actual circumstances. As far
back as the late 1950s there were hollow-state ham rigs made
that were meant for 50 ohm loads only. In fact, there
were some HF tube ham rigs made that required no conventional tuneup
at all (CE 100V, 200V, 600L).

Certainly I can see one of my newer rigs start to fold back at 2:1.

Most hollow-state ham rigs can handle 2:1 SWR no problem.
Sometimes there is less tolerance for loads that are highly
reactive, though.

What are the practical limitations of the Tube finals apparent
flexibility?

It's really a matter of how the rig was designed.

Many 1950s hollow-state ham rigs were built with pi-networks that
could match a wide variety of loads efficiently. The EF Johnson Viking
2 is a classic example of that type. Many
homebrew designs also had such pi-networks.

The problem is that the components for such a wide-range network tend
to be large, heavy and expensive. So in the late 1950s and early
1960s, rigmakers designed more for compactness than for wide matching
range. Still, the typical
ham rig of those days could usually handle SWR of 2:1 or
less with no problems.

Is it safe to compare the load, plate, and drive controls to some of the
functions of a tuner? (possible real dumb question)

Not a dumb question at all IMHO.

The short answer is "no". Tuning up a hollowstate
ham rig is a similar but not identical to adjusting the
typical tuner.

Some may tell you that all it takes to tune up a tube
transmitter is to "peak the grid and dip the plate", but
that's simply not correct. Tuneup procedures vary
according to rig design and you have to be specific.

Of course once you get the hang of it, the procedure
rapidly becomes second nature.

What specific hollowstate rigs are you considering?

73 de Jim, N2EY

On Mar 4, 12:53?pm, wrote:
On Mar 4, 12:48?pm, Mike Coslo wrote:

Some may tell you that all it takes to tune up a tube
transmitter is to "peak the grid and dip the plate", but
that's simply not correct. Tuneup procedures vary
according to rig design and you have to be specific.

Sorry, but that was procedure for pre-WW2 high-
power HF transmitters. While it is a simplistic
phrase, it still applies. A more exact procedure
was to tune up the exciter with reduced drive
power and literally peak the grid current. Plate
current was then observed with the plate tuning
adjusted for a slight, but observable dip in plate
current. Of (perhaps) greater importance was setting
the neutralizing control for minimum grid current;
"dipping" the plate current should produce the least
grid current peak on adjusting the plate tuning.

For best results on setting the load-side capacitor
of the common pi-network without a bidirectional
power meter, a detector way out in the field with
meter next to the transmitter is the simplest way
to "tune" that capacitor. However, with about 34+
other high-power transmitters all in the antenna
field, that is impractical; presets for that control
would suffice. The load capacitor of a pi-net has
the least effect on tuning to a new frequency.

When someone does about two QSYs per shift
on at least 15 different transmitters with pi-network
output circuits (all with vacuum tube PAs), yes,
one "gets used to it" but what I described was the
correct phrase.

The pi-network has been around and used in HF
transmitters since at least the late 1930s and has
survived past the start of the semiconductor era.
However, the convenience of broadband transistor
power amplifiers has pretty much tossed that whole
tube tuning procedure. Used with a Bruene detector
sensor for an automatic antenna tuner, it makes
QSYing a snap, even jumping bands (with a broad-
band antenna, of course).

"Peak the grid and dip the plate" is an old correct
phrase. It will be found mentioned in the current
US amateur radio question pools.

Yes, there are exceptions. I was once involved with
a distributed amplifier design that would cover over
an octave of spectrum using tubes and was NOT
tuned at all in normal operation. Since that one
involved over a dozen vacuum tubes (ceramic-metal
medium-power types), it would not be suitable for
ordinary amateur radio HF transmitter stations. The
vertical amplifier of the old Tektronix 54n series
oscilloscopes used push-pull tube-type (all glass
envelope "receiving" type) distributed vertical deflection
amplifier.

The pi-network output circuit was a favorite among
amateur homebrewers for decades due to its
simplicity and better ability to attenuate harmonics,
that coming to be more and more prominent in
regulations as HF users became more plentiful.

On Mar 4, 11:21 pm, "
wrote:
On Mar 4, 12:53?pm, wrote:

On Mar 4, 12:48?pm, Mike Coslo wrote:
Some may tell you that all it takes to tune up a tube
transmitter is to "peak the grid and dip the plate", but
that's simply not correct. Tuneup procedures vary
according to rig design and you have to be specific.

Sorry, but that was procedure for pre-WW2 high-
power HF transmitters.

Sure it was.

While it is a simplistic
phrase, it still applies. A more exact procedure
was to tune up the exciter with reduced drive
power and literally peak the grid current. Plate
current was then observed with the plate tuning
adjusted for a slight, but observable dip in plate
current. Of (perhaps) greater importance was setting
the neutralizing control for minimum grid current;
"dipping" the plate current should produce the least
grid current peak on adjusting the plate tuning.

A number of amateur transmitters/transceivers have used a quick
peaking of the drive/preselector control followed by adjustment of
tune and load controls for maximum output, keeping readings within
operating parameters. I've never seen an amateur transmitter with a
front panel neutralizing capacitor. Neutralization is normally a set
and forget procedure which one needn't worry about until the final
tubes are replaced.

Tuning for maximum output for a given amount of drive has become the
norm in tuning high power, vacuum tube linear amplifiers. All one
needs do is make certain that the bottles don't aren't drawing too
much grid current. A check of linearity can be made with the station
monitor 'scope.

The load capacitor of a pi-net has
the least effect on tuning to a new frequency.

That would depend upon the antenna being used and the amount of
frequency change as well as the type of equipment being used. Some
manufacturers switch in some fixed capacitance on various bands or
portions of bands.

The pi-network output circuit was a favorite among
amateur homebrewers for decades due to its
simplicity and better ability to attenuate harmonics...

....but the Pi-L did a much better job of attenuating harmonics with
only a little more circuit complexity. Quite a number of Novice
licensees found themselves in receipt of OO notices or letters from
the FCC when using a simple pi-net output tank with a multiband
antenna.

Dave K8MN