I am an electronics hobbyist. I designed this tube AM transmitter circuit. I want to ask you, since it's my first designed circuit, if it will work, and if I can improve it.
I am using a PL500 for the big tube.
Here is the schematic:
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2 Answers
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No, it will not work.
There are about five major issues, nevermind the absent part numbers and component values. There also isn't any modulation going on; if we are to assume the input (if that's what that is; several symbols are nontraditional here) is an audio signal, where is the RF coming from, and how is it being modulated? Or if RF, where does the envelope come from? In short, what makes this specifically an AM transmitter, and not just a linear amplifier?
Indeed, given some component values, this seems closer to an audio amp than RF.
Start with the basics:
- Why do you want an AM transmitter?
- What does it need to do? Center frequency and bandwidth, power level, modulation index, distortion, etc.
- Why tubes? If this is a learning project, why not an easier circuit to work with e.g. audio frequency? Do you have an oscilloscope, spectrum analyzer, impedance analyzer, etc. to do any RF work?
- If you just want a basic low power transmitter for around-the-house use (say, local broadcast to vintage radios), there are existing solutions for that; likely, whatever signal source you would still need for the above circuit, would already do (by itself), given a suitable matching network and a large (room sized) loop antenna. Very little power is needed, and at these wavelengths (AM BCB) it's all about antenna size.
- Unlicensed and poorly designed transmitters are widely frowned upon, by users of airwaves (HAMs etc.) as well as the authorities. Do you have any suitable qualifications for operating this? (As well as qualifying its performance as above.)
As well as the directly relevant questions, the above also suggest directions to read up in: radio design and operation; circuit design; RF amplifier design; AC analysis; antenna theory; etc. Good luck and stay safe!
answered Jun 5, 2022 at 20:30
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\$\begingroup\$ I changed the schematic. I hope it is better now, if not, please explain to me what I should change because I'm not so good at this. About transmitting, I will make it quite weak, so it it only covers my property and doesn't interfere. \$\endgroup\$ Jun 6, 2022 at 14:26
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\$\begingroup\$ @GeorgeChita General tips: electronics.stackexchange.com/questions/28251/… (most of these you're fine on, as far as layout), you can also create nice schematics in your question: electronics.meta.stackexchange.com/questions/963/… though they don't have tube symbols and I don't see a way to add custom graphics, unfortunately. Anyway, look up the usual connector and tube symbols, that will help with clarity. \$\endgroup\$ Jun 6, 2022 at 14:54
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\$\begingroup\$ I'm 14 years old, so I may have messed up again, I don't have experience in this. I tried to use an Armstrong oscilator and combine the carrier with the signal I want to transmite. Sorry for the symbol for audio input. The site I used didn't have that symbol, so I improvised. I hope it's ok now! \$\endgroup\$ Jun 6, 2022 at 19:44
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\$\begingroup\$ Also, this is the simplified schematic, I will add filters and other things to improve audio quality but I just want to know if the idea works. \$\endgroup\$ Jun 6, 2022 at 19:45
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This PL500 is nice to look at but not a good choice for a start. It is designed for a power range of around 20-60 W and it is far from easy to let it run at only e.g. 10 mW.
Why not start with a simple FM valve radio using low voltage tubes like this:
And yes, while it's a receiver it also emits a very small amount of RF..
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