Im getting everything ready to start broadcasting in 1620 AM. I got a old tube type AM transmitter (some zenith model) but the problem is that it has a maximum output of 100mw....(disappointing) how far would that broadcast? Im using a 40 foot antenna with a huge loading coil and a cold water pipe as ground.
I have been thinking of maybe building a linear amp, but haven't had any luck finding schematics for AM circuits, they are all FM. Are there ones you would recommend, or could I modify the transmitter to get more juice out of it?
The final tube is a 6j5 triode. Could I replace that with a 6SN7 tube? I know that a 6sn7 tube is two 6j5 in one tube. Would that work?
sorry if this post is long. Im just super excited to get on the air!
As long as your antenna is tuned to the transmitter correctly you should get a mile or two of range I would think. 100mw part 15 transmitters usually get 1/4 mile range on an average radio, but that's within the regulations. Since you're using a much longer antenna then the legal setups use you could get double or more range. This all depends on many factors like how wet the soil is for your ground, the amount of modulation you are broadcasting with, and how well tuned the antenna is.
That site and PDF book helped me a great deal with antenna ideas, setup, and even schematics.
I would worry about building an amplifier after you already have had fun and setup your 100mw transmitter correctly. It's best to practice with low power first to get your hands dirty, then move on to bigger things
Oh on the tube, you can't just put any old tube in there. Each tube number has different pinouts and require different bias/dc voltages. The most you could do is increase the dc power to the plate of the tube, but that's beyond the scope of what I can help you with at the moment. If you can find a schematic of the transmitter that would help. Make sure it doesn't have a build in loading coil as many legal part15 transmitters do. If it does, bypass it so you can use a "real" antenna.