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Amps. I
have known! ---------
It isn't the objective of this
Web Page to teach people all about RF Linear Amplifiers, but to show the
different sorts of approaches that Amateurs take when "Home-Brewing".
Still a few words to explain what you may hear on the air will not go amiss.
The rest you can find in books etc. There are a number of amplifier designs to
choose from, but for Single Side Band use it must be in the Linear Class. This
for practical considerations, usually takes the form of Class A through to
Class B operation mainly defined by the type of Tube (Valve) used. For SSB
Amplification the choice is usually AB1 if using multi-grid tubes and Grounded
Grid when using Triode tubes. There is nothing wrong with running a Linear
Amplifier in Class A, but practically this class is very inefficient and
although theoretically quoted at 50% efficiency, in practice is more likely to
be around 25% - 30%. Similarly a Triode can be used in AB1, but because Class
AB1 operation requires high peak anode current without Grid Current, these
conditions are better met by multi-grid tubes. The other option is
Grounded-Grid using Triodes which is a Class-B operation and although not as
efficient as AB1 requiring much higher drive power. It is very popular due to
the simplicity of design, Interfacing with the higher power transceivers on the
market and requiring a low component count. Class AB2 has not been addressed
because it is far more stringent on its requirements due to the higher driver
power required and very good regulation of the drive source, however it is
sometimes used. Many styles of layout and construction are used depending on
what is in the "Junk-Box" and here I have amassed a collection of a
few. This is an example of a Home made Grounded grid amplifier using the good
old favorite the 813 and although only rated at 125W anode dissipation, two are
capable of running up to over 400W output. For operation in this mode the
Screen and Grid are often connected together.
There
are also other tubes that are very similar and find themselves in Home Brew
Amps. This is an example of the QB4-300, 
two
of which will run at around 1KW. A smaller version of this was the QB4-125
often called the miniature 813! Moving into the AB1 class, the Ceramic Tetrodes
have been a good choice for many years and many VHF/UHF Amplifiers have sported
them. This is an example of a HF Amp using a not very well-known tube the
4CX300A, 
a
neat self-contained unit that would be capable of around 600W output. Using the
4CX1000A in a different configuration is this Class 
AB1 Amplifier which is the property of
VK2ABN, here the output circuit includes a variable Inductor as well as the
capacitors to obtain the optimum matching on every band.
We are not sure what the foot contributes!
Still further up the QRO scale
and
unfortunately a large picture of this isn't available, is this beast. This uses
a pair of 4CX1000A's and also makes use of Vacuum variable capacitors.
Amplifiers of this size can run up to 2/3KW depending on the anode voltage and
PSU current capabilities. As a final one for now and addressing those of us
that have BIG ideas, these are a few pictures of the REAL QRO stuff using the
YC156 
and
it makes you wonder who pays the electricity bill.
Certainly
I would think that a good 3-phase supply, large antenna insulators and most of
all a good dummy load,
this unit is rated at 6KW and is
water-cooled! Finally the beast without its remote control shown complete 
I hope you enjoyed that, the
author has actually worked a station in
As have previously said, many
people send me photos that may be of interest and here is one from Derek
ZL1BOQ. Here he has made good use, with a little ingenuity, of a surplus RAF
amplifier to create a Linear Amplifier affectionately called "Big
Bertha".
Hardly micro-technology and possibly a doubtful candidate for a 1st floor location, but I'll guarantee it keeps going for years!
This
is an interesting project undertaken by the author which is converting an old
Dentron Clipperton-L to more modern tubes. The tubes used are the GI7-B Russian
Triodes and can be easily cooled using the original Fan. They are far easier to
drive and also much cheaper than the original 572B’s
The
holes for the original tube sockets can be clearly seen in the bulkhead on the
left