Circuit diagram of AM Modulator based on triode valve/tube

Why use a tube? What are your specifications?

Frank

Hello, Thanks for the reply. I am actually doing a piece of work for my University course investigating the key advantages and disadvantaged of high and low level modulation of AM transmitters. I was hoping someone had something I could use.

Regards,

Robert.

Frank Raffaeli wrote:

Lots of stuff on here. Took me 30 seconds using Google.

Look under "Transmission Of Signals".

Where you will find some modulator circuits using triodes

Plate (anode) modulation:-

Grid modulation:-

a Class C amplifier with plate modulation from a Class B modulator:-

Go to a library and find an ARRL Handbook from the years 1935 to 1970. Those have several chapters on AM modulation, with theory and actual working transmitters and modulators.

The "Theory" in these books is not quite up to EE textbook standards, but good enough for most purposes.

BTW did you know it's possible to make a very good AM transmitter by taking an old tube AA5 radio, swapping the audio output and converter tubes, and moving 4 wires? Cool^3 IMHO.

Now that you know it can be done, doing so is left as an exercise for the reader :)

Thanks for the clarification. Here are some interesting papers on broadcast modulation:

Frank

Take a look at the Harris digital AM transmitters. It will blow your mind away.

Tam

Which generation? The first units had TO-3 final transistors, and a CPU board to monitor the transmitter. There were more computer problems than failed RF trays, so later version left it out. Then, the RF output went to plastic packages. They are interesting transmitters but are more expensive to repair, at times. WQBQ has one of the first built, and the engineering room had a large pile of unrepairable RF trays, and other modules the last time I was there. Some failures cause the PC boards to overheat and burn large holes.

I got my info from a local broadcast engineer who had done some work at WLW. I think his link lead me to a DX60. I had not heard of problems, and it is still an awesome way to do it. Anybody learning about AM modulation should at least be aware of it.

Tam

How do they stand up to lightning?

Not as well as the older tube transmitters. The old 5 KW Gates tube transmitter might trip the plate relay at WLBE in the Leesburg/Eustis area, but it could be remotely reset by the engineer over his cell phone.

I have heard that the later Harris are better at handling lightning strikes, but I haven't seen one in operation. I have pretty much quit doing broadcast engineering consulting, due to health problems which is OK, because the stations have pretty well replaced the older equipment that their young engineers didn't understand.

Have you ever seen the experimental 500 KW transmitter WLW used in the '40s? Now, THAT is a real transmitter!