Short wave Valve transmittor :) what valve is best?

[sco1t]

Hi, I'm just confused about something. A lot of them circuits have no cathode resistor. I thought a valve needed a negative bias on it's grid to work?

[freax]

just build this: iTx - Tube AM Broadcast Transmitter Kit | eBay

Its safe, legal, and it won't give you a big nasty fine!

Also look at the 90v battery eliminator that is for sale in that eBay store. http://www.ebay.com.au/itm/90-Volt-B...item27cc8bf5db

Ontop of that it doesn't put other peoples lives at risk.

Legally you cannot build a transmitter at all, not unless you are a technician class ham, know why that is? do you have a frequency counter? a spectrum analyzer? an oscilloscope? a swr meter? a dummy load? a all of these bits of equipment are /necessary/ to test your homebrew transmitter before it gets an antenna hooked up to it, ontop of that you could end up burning out component after component because the antenna isn't perfectly matched.

Don't use tubes, use either that kit, something that has been proven, tested, and relied upon, or use transistors.

If you are going to be a giddy goat and use tubes anyway then get this thread moved to the tubes section so the right people can have a gnaw at it and maybe recommend something that they know won't cause any harm to the shortwave bands.

Just click on the exclamation mark on the left hand side of any post /!\ and type in: hi, could I get this thread moved to the tubes section please? as it involves tubes Thank you.

[Joe Roberts]

Its safe, legal, and it won't give you a big nasty fine!

It might be safe but read the fine print...not legal anywhere in the EU unless operated within a shielded enclosure.

[sco1t]

I have most of that equipment yes. I've made loads of tube amps and tape player, recode preamps. I've just never done anything with high frequencies yet, so I'm mainly just doing this to learn

[freax]

Originally Posted by Joe Roberts

It might be safe but read the fine print...not legal anywhere in the EU unless operated within a shielded enclosure.

Indeed, hence the necessary caution needed over this thread.

EU R&TTE directive and EMC Directive 2004/108/EC - in order to purchase this item, you must agree that:-

1. You intend to export the item to an address outside the European Union. Under no circumstances will this item be resold or put into service within the European Union.
or
2. The item will only be used within a completely RF screened and shielded metal enclosure or environment for testing, evaluation, experimental or laboratory purposes and any other use that does not radiate electro-magnetic waves into free space. I am not an unqualified end user and I have RF engineering and electromagnetic compatibility skills at my disposal.
or
3. For use by a Licensed Radio Amateur on 160M Band (Kits Only)

It basically means that if you are buying it within the EU you must put it into a metal enclosure, including your radio and your house.

Man those laws are pretty strict huh.

[Wavebourn]

Originally Posted by sco1t

Hi, I'm just confused about something. A lot of them circuits have no cathode resistor. I thought a valve needed a negative bias on it's grid to work?

What I described above, is called "Grid bias". AC that the rube generates is rectified on it's grid and applied as a negative bias. Such a way it stabilizes level of AC that it generates. When anode modulation applied from anode of SE amp, the tube's transconductance changes with anode voltage following audio frequency modulating signal. That changes level of AC radio signal that it generates.

[Joe Roberts]

It basically means that if you are buying it within the EU you must put it into a metal enclosure, including your radio and your house.

Man those laws are pretty strict huh.

You are also not allowed to smoke inside the enclosure.

[sco1t]

Hi Wavebourn, I didn't know a valve could get it's negative bias in such ways
Thanks for the help

[sco1t]

the laws are not that strict on radio transmitters in the uk, if they were how could they sell these small fm transmitters in the most uk shops Buy Belkin Tune FM Transmitter at Argos.co.uk - Your Online Shop for MP3 accessories.
they transmit over 10 meters ?

and there is worse I could be doing then transmitting Womack and Womack for over 2 meters of air to a 1950's radio :P

[freax]

Originally Posted by Joe Roberts

You are also not allowed to smoke inside the enclosure.

I think its about time you guys (everyone in the EU) start petitioning for free-range radio waves...