6N7 Tube QRP Power Amplifier - One Rainy Day DIY Project

Once upon a time I'd decided to join a Big Guns Gang and made a Super-Duper Powerful Vacuum Tube QRP amplifier for my 800mW QRPP homebrew telegraph vacuum tube transceiver "3T" (I promise to write a separate article or two about this three tube transceiver project later). It was not an easy decision to me because for that legendary time I'd almost a year used the QRPP power of less than a watt, but there was a rainy spring day, I've called CQ again and again without any takers and, at very last, somebody took over my only rock bound frequency. "That's all" - I said - "Enough!" ..and turned on my Soldering Iron.

Let me describe the scheme. Grounded-Grid design has been chosen because it is simple, easy to matching to coaxial impedance, provides the necessary level of amplification and typically requires no neutralization. After several experiments with triodes and double triodes I'd chose a 6N7S (6H7C) valve - Russian glass shaped version of well known 6N7 vacuum tube. I know that there was a 6N7G and 6N7GT American glass tubes, but as I heard these ones was not as common as metal 6N7.

Simplified Amplification

There was a Book Of The Books in early 1970's - "Amateur Radio SSB Equipment" by S. Bunimovich (UB5UN) and L. Yailenko (UT5AA). Funny, but this book can be found in a common pirate's shack as well as in an Extra-class (1-st xUSSR category) HAM one. Yes, xUSSR pirates used AM only (mainly?), but this book was a great source of knowledge about tubes, transmitting equipment etc for everyone who been proud to heat The Ether.
There is a huge pile of a very complex things that described so comprehensible in this book, such as Phase Shift SSB Modulators, complete Transmitters, SSB Receiver's features, Dynamic Biasing and much more, but it is too hard work for me to translate all of those great articles and I decided to start with exposition of pair of a Ground Grid Linear Amplifiers - so simple, not so powerful, but namely these amplifiers was most popular in 1970's. Thought, every xUSSR HAM made one of these amplifiers and used one with a great success.
As for me, I did :)