[SOLVED] Learning about HF tubes amplifier design

[goldsmith]

Hi guys
I know that at very very very high frequencies , and high powers at that frequencies , we have to use from vacuum tubes.
but how can i learn about them and how can i design them.
Is it possible that you guide me , please?
Thanks in advance
Goldsmith

 

[FvM]

You should be more specific about your range of application, particularly frequency and power.

Regular vacuum tubes aren't particularly suited for very high frequencies, they hardly achieve a few hundred MHz. It's different for special vacuum tubes based on travelling waves, e.g Klystrons and cavity resonators like Magnetrons. But their circuit technlogy is completely different from regular vacuum tubes.

 

[goldsmith]

Dear FvM
Hi
Thank you for your reply. i saw a vacuum tube that can work at 1GHZ frequency and 700 watt out put power . but how can i design with these vacuum tubes e.g the tubes that you said . and why they are different with together ?
Appreciate
Goldsmith

 

[FvM]

My tube experience is limited to radio and TV receivers, audio PA and magnetrons.

But there are many ham (amateur radio) related internet pages sharing RF power tube stuff. Also vacuum electronics text books and RF engineering hand books.
Here's e.g. a site with tube data sheets RF Tube data, Power Amplifiers, YC156, application notes - G8WRB

 

[betwixt]

I fully agree with FvM. I have used normal vacuum tubes at up to about 800MHz but beyond that their performance is poor. Even at 800MHz a single transistor amplifier far out-perfomed the tube version.

The problem is that vacuum tubes have inherently high inductances in their connecting wires, have relatively large capacitance between electrodes and unless used in grounded grid configuration, tend to have too much feedback capacitance which makes them unstable. Usually, feedback compensation is needed to cancel the instability.

This isn't the place to explain how TWT work but the principle is to use special materials to slow the signal so it has chance to 'bunch' (accelerate and decelerate) the main tube current. They typically require several KV operating voltage and high power types have to be water cooled.

Klystrons and Magnetrons are not amplifiers as such, they actualy produce the output signal by oscillating themselves although some Klystron types can be fed from external signals. I have always explained Magnetrons as working ike this:

Imagine blowing across the top of an empty bottle, if you get the flow just right you hear a steady tone. The size of the bottle determines the pitch of the tone. The sound is produced by a resonance of the air pressure waves inside the cavity formed by the bottle. Substitute an electron flow for your breath and make the cavity very much smaller, as the electrons skim the entrance to the cavity (like the mouth of the bottle) it sets up an oscillation. A strong magnet is used to bend the electrons so they pass at the optimum angle. Most Magnetrons use multiple cavities arranged in a circle, the oscillation in each cavity reinforces the next to give it more gain. So a Magnetron is a diode with a twisted electron beam that makes a 'tone' as it passes the cavities. The downside to magnetrons is their frequency is decided by the cavity dimensions so they can't easily be tuned to different frequencies. They also run on high voltages, usually in the 2 - 3KV region and can fraw several amps so they must be force cooled.

Brian.

 

[kak111]

Some reading about HF microwave tubes......

Klystron - Wikipedia, the free encyclopedia
**broken link removed**

Cavity magnetron - Wikipedia, the free encyclopedia
Radar Basics - Magnetron

Radar Basics - Crossed-Field Amplifier (Amplitron)

Traveling-wave tube - Wikipedia, the free encyclopedia
**broken link removed**

Western Electric 700er-Serie Übersicht

 

[goldsmith]

Thank all of you for your helpful guidance .
Regards
Goldsmith