This page is a detailed description of my 6CL6 and 807 valve transmitter. I have been asked many times, why did I decide in 2012 to use 100 year old technology to built a transmitter. My answer is that "fun" is not necessarily embedded in "functional". I therefore claim that valves can be fun despite not being the best performers compared to solid state. The reality is that most amateur amateurs like me would have extreme difficulty producing from scratch a transceiver with the same performance and functionality as the standard, sub-$1000 HF radio you can buy from a shop. Should that bring the end of a hobby that has traditionally been about making things? Probably not. The valve radio technology does exactly that for me: it satisfies my desire to make a radio from scratch. It has the extra twist that components required are hard to come by. This makes me first understand and then come up with creative solutions that do not require these components. Or, hunt them down until they are found. Hunting can be fun, I assure you.
Another argument that I hear often is that amateurs must continuously be technology leaders. My opinion is that this is great when it happens but it is not a requirement to obtain an amateur license and have some fun with it. In fact, as long as one continuously breaks personal barriers in knowledge (in any field), then surely, that's not a waste of time.
But there are other, maybe sillier, reasons that make valves exciting. How could one ignore the aesthetically pleasing shape and filament glow of a valve! The reason behind choosing an 807 instead of the 6146 was exclusively aesthetic - the "coke bottle" or "stubbie" shape of the 807 simply cries radio to me compared to the more industrial looking 6146. The 807 has also a great history behind it, being used extensively in WWII. And those were the pioneering days of radio. I am happy to report that I am not the only one fascinated by the shape of the 807, see the G3PPR reference at the end of this page. The amateur service was clearly important to manufacturers back then since there was always a reference to how an amateur could make use of that valve (see ICAS ratings). A good percentage of the components used in this radio (valves, panel meters, RF chokes, etc) are either new old stock or salvaged from equipment of those golden days of radio. Let's not forget the construction technique, typical (but not exclusive) for a valve rig. There are no PCBs to hold the components, the components are simply suspended in a 3D web giving that unique look to the final product. Nothing but a soldering iron and some imagination is required for the component layout.
The schematic above has already been altered. I have added screen modulation via a transformer (and a resistor for improved linearity). This has been tested on air and seems to work reasonably well.
The 807 TX is configured for 40m (7030 kc) CW. It now has a grid bias partially from a cathode resistor and partially from a grid leak resistor. It produces 20 W of power with about 500 V plate voltage and about 72 mA cathode current. There is a relay for T/R switching and there is also the ability to select oscillator and PA keying or PA keying only.
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