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... :-)

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, 5:48 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.

I don't know if "finicky" is a good term, Mike. "Different" might be
the best word to use. Transmitters with vacuum tube finals can match
a wider range as a rule, but there is a limit to what they can
handle. Some of the older Johnson and Globe/WRL rigs matched a wider
range than some of the other brands.

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

Most Japanese gear is designed to do just what you're experiencing.
That's a form of protection for the final transistors. Ten-Tec does
it differently. Ten-Tec rigs do not start to reduce power. They
depend upon the supply to fault and trip if too much current is
drawn. That's why it is important to use a Ten-Tec supply with them
or to use a fast breaker rated to trip near the maximum current draw
expected of the transmitter.

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

That depends entirely upon the design specifications set by the
manufacturer.
If the manufacturer's manual says "45-90 ohms", that's the practical
limitation.
Some of those old Globe transmitters used to have ranges of up to 1000
or 2000 ohms as I recall. At the other end of the spectrum,
Hallicrafters produced some transmitters without even a loading
control. These were designed to be used with an antenna presenting
something very close to 50 or 75 ohms.

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

Not the "drive" control, but certainly the other controls of a tuner
could be considered comparable to the "tune" and "load" controls.

If the only antennas we have are trapped verticals, tribanders or
dipoles/inverted vees cut for the band to be used, we might get away
with not having to use a tuner at all. Still there are likely to be
frequencies significantly removed from the antenna's resonant
frequency where one might need a tuner to enable the transmitter to
make full power. We aren't likely to need a wide range tuner for
those times. A simple T-match will likely enable us to find a
combination of settings which will present a low VSWR to the
transmitter. The main alternative is to have a variety of antennas
which present a VSWR of under 2:1 to a transmitter.

Dave K8MN

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.

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 -


Most quality built amps will cover 2-30mhz, they only need the proper
filters behind 'em to keep 'em clean, and of course, you exciter needs
to put out a clean sig.

Motorola has a great circuit using four 250W transistors to get you a
kilo. It can be found on the web.

There are scores of tech papers by motorola on 100W to 1K and beyond
amps, a little research on the web should discover them.

JS
--
http://assemblywizard.tekcities.com

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.

" 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 -

wrote in
oups.com:


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)

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.

I enjoy twiddling knobs, kind of the same way I like a manual
transmission. 8^)


What specific hollowstate rigs are you considering?


Last year at Dayton I purchased a 40 and 80 meter Heathkit single
Bander as a learning tool - they are pretty simple. I restored the
80 meter unit, and will start on the 40 meter one sometime. I am now
looking at a Kenwood TS-830S. It's a hybrid, with tube finals. I
really like it so far, although I don't see it replacing my IC-761.
I am hooked on computer control of the newer rig - sometimes! Other
times I just like that retro aspect.

- 73 de Mike KB3EIA -

wrote:

If the only antennas we have are trapped verticals, tribanders or
dipoles/inverted vees cut for the band to be used, we might get away
with not having to use a tuner at all. Still there are likely to be
frequencies significantly removed from the antenna's resonant
frequency where one might need a tuner to enable the transmitter to
make full power. We aren't likely to need a wide range tuner for
those times. A simple T-match will likely enable us to find a
combination of settings which will present a low VSWR to the
transmitter. The main alternative is to have a variety of antennas
which present a VSWR of under 2:1 to a transmitter.

That brings up a related issue. Lots of Hams today are restricted to
one antenna, yet they would like all band operation. I think it would be a
great idea for a manufacturer to have a transciever that included a tuner
right in the rig itself.

- 73 de Mike KB3EIA -

"Mike Coslo" wrote in message
6
wrote:

If the only antennas we have are trapped verticals,
tribanders or dipoles/inverted vees cut for the band to
be used, we might get away with not having to use a
tuner at all. Still there are likely to be frequencies
significantly removed from the antenna's resonant
frequency where one might need a tuner to enable the
transmitter to make full power. We aren't likely to
need a wide range tuner for those times. A simple
T-match will likely enable us to find a combination of
settings which will present a low VSWR to the
transmitter. The main alternative is to have a variety
of antennas which present a VSWR of under 2:1 to a
transmitter.

That brings up a related issue. Lots of Hams today are
restricted to one antenna, yet they would like all band
operation. I think it would be a great idea for a
manufacturer to have a transciever that included a tuner
right in the rig itself.

- 73 de Mike KB3EIA -

They do exist, although being primarily interested in VHF/UHF operation
(we only recently had the morse requirement for HF dropped over here in
the UK, but that's another topic..!!) I've had little experience of them.

I do remember vividly using a Drake commercial HF transceiver (I think it
came out of a ship's radio room) back in the late 80's at a special event
station that had this feature, you could operate on any band without any
form of tuning at all, although of course how much power would get out on
a really bad antenna is debatable ;-)

Of course if you've enough money, there are those antennas that tune
themselves. A friend has a 3-element beam that is computer controlled; as
you tune across the bands, the elements automatically adjust themselves to
the correct length..! I don't recall the make/model, but it is of American
origin, does anyone know of it..?

73 Ivor G6URP