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Simple AM transmitter with one Tetrode vacuum tube

Fluffyboii

New Member
Hi, my local electronic store has lots of radio tubes brand new in boxes. I don't recall exact part number but basically they are all simple tetrodes. All of the AM radio transmitter designs use pentodes or other vacuum tubes with more pins. Is it possible to build one with a tetrode. I want to use my old radio to play music from my phone nothing special. I am aware there are simple circuits like 555 timer or crystal oscillator ones but I want this to be a little nostalgic. Or should I make a 555 circuit and use a vacuum tube to amplify the output power. I am not experienced at designing circuits so any help would be appreciated.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
Hi, my local electronic store has lots of radio tubes brand new in boxes. I don't recall exact part number but basically they are all simple tetrodes. All of the AM radio transmitter designs use pentodes or other vacuum tubes with more pins. Is it possible to build one with a tetrode. I want to use my old radio to play music from my phone nothing special. I am aware there are simple circuits like 555 timer or crystal oscillator ones but I want this to be a little nostalgic. Or should I make a 555 circuit and use a vacuum tube to amplify the output power. I am not experienced at designing circuits so any help would be appreciated.
You shouldn't do this as it's highly illegal!.

A simple one tetrode AM transmitter easily covers 25+ miles!.
 

unclejed613

Well-Known Member
Most Helpful Member
https://en.wikipedia.org/wiki/Carrier_current
carrier current transmitters use the power wiring in your house as an antenna. there are legal power limits for carrier current transmission, mostly to prevent the signal from radiating more than a few feet from your house, however inside the house you will get useful signal. carrier current transmission is legal in most countries. you will need a coupler that couples the signal into the power cord of the transmitter, and there are a few safe ways of doing this, and a lot of ways that aren't safe. perhaps the safest is to wrap the power cord around a toroid core, and also wrap what will become the antenna coil of the transmitter alongside the power cord. this way you get isolation from the power line and couple the signal into the line and neutral conductors of the wiring in the house.
 

BobW

Active Member
Nigel lives in the UK where everything is illegal. If you live in North America, it is legal to build a very low power AM transmitter. You are limited to 100mW and an antenna no longer than 3 metres (10 feet). Here is one that I designed. It certainly won't transmit anywhere near 25 miles. It barely gets out of my house. It uses a dual section tube, any one of 6U8, ECF82, 6CQ8, or 6GH8A. Audio quality is very good.

 
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Fluffyboii

New Member
Nigel lives in the UK where everything is illegal. If you live in North America, it is legal to build a very low power AM transmitter. You are limited to 100mW and an antenna no longer than 3 metres (10 feet). Here is one that I designed. It certainly won't transmit anywhere near 25 miles. It barely gets out of my house. It uses a dual section tube, any one of 6U8, ECL82, 6CQ8, or 6GH8A. Audio quality is very good.

I live in Turkey and no one uses AM band anymore, can I use 2 seperate tubes instead of this one cus I don't know if I can find this.
 

atferrari

Well-Known Member
No matter how ilegal that could be (or not), you have chances, even with low power, to become an annoying interference.

I happily did so, when building my first xmtr in the 40 / 80 m bands.

Except in their oven or the cold water taps, my neighbors had me everywhere.
 
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BobW

Active Member
Agreed. Even if it meets power and antenna regulations, it's still illegal to cause interference.
 

unclejed613

Well-Known Member
Most Helpful Member
this uses two tetrodes, one as the RF amp, and the other as the modulator... the modulator controls the plate current in the RF amp by audio modulating the cathode voltage. the 12AT7 (ECC82 if i remember correctly) is the crystal oscillator as well as the modulator preamp (one half of the tube for each).
https://www.k6prk.org/CARRIER CURRENT AM TRANSMITTER.HTM the antenna is the AC power line, so any AM radio in the house will receive the signal with good signal strength. the characteristics of low power medium frequency radio waves insure the signal doesn't go far, and AM band carrier current transmissions are blocked by the pole transformer, isolating your house from the overhead power lines.
 

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