![]() ![]() ![]() I use a Pi tank circuit to couple the output signal to the antenna. The oscillator is a 2E26 configured as an Electron-Coupled Colpitts crystal Oscillator, which is capacitance coupled to the modulated RF amplifier. The speech amplifier is a 6AU6 providing 155 gain followed by a 12AU7 configured as a self-balancing phase-inverter. I like to add screen in the description since you have to modulate both the plate and screen of a Pentode to reach 100% modulation. It uses a pair of 6L6GC tubes in Class AB1 push-pull generating between 15 and 20 watts of audio power, high level plate and screen modulating a 6146. The result is a 40 and 80 meter 20 watt high level plate modulated AM transmitter. In total, I spent about 2 months on this build. ![]() I had no help from an Elmer so I had to work through all issues on my own which took time. ![]() I’m not going to say that this project was easy because it wasn’t. It was at this point that I decided to go all out and try to build a plate modulated AM transmitter. After successfully getting a simple amplifier working I began experimenting with oscillators. After getting a basic understanding of tube theory, I started experimenting with simple Class A1 triode amplifiers. I had to start with the basics of how vacuum tubes work. Although I’m not a stranger to electronics per say, I had never built anything using vacuum tubes. I purchased a copy of the ARRL 26th edition, 1949 “The radio amateur’s handbook” and started reading from page 1. This prompted me to take the plunge into home-brewing. I also noticed some nonlinearity in the RF envelope. It uses Heising modulation, and is only able to do at best 80% modulation. This Novice rig from the 50s works fine, but it does leave something to be desired in the modulation department. I’ve restored a number of vintage radios over the years, but recently got the homebrewing bug.įor years I used a WRL Globe Scout 680 on the 20 and 40 meter AM windows. There’s nothing like bringing an old boat anchor back to life and getting it on the air. I also like operating vintage AM tube gear as well. I’ve always been intrigued by long distance communications on the HF bands and enjoy communicating with stations from around the globe. I’ve been an amateur radio operator since 2001 and a short wave listener for a number of years before that. ![]()
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