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cavity tube amplifier

doubty

Member
Sep 20, 2009
6
0
11
Hi,
I am new here.. I don't know whether this is the correct place to start the thread. I need to make a 1 kW 75 MHz amplifier using 5CX1500A. I have tested one successfully using pi L-C matching network. I do not know much about coaxial cavity based amplifiers. I would like some guidance to make a 2 kW amplifier at 75 MHZ and 350 MHz using coaxial cavities over 5CX1500A pentode.
From what I have understood, the cavity should be at least lambda/4 long with movable shorts. provision for cooling and dc isolation are required. Coupling can be loop or capacitive type. There should be an anode tuning capacitor. Please correct me if I am wrong. How is the ideal position of the coupling decided? What are the moving/tuning parts in both types of coupling?
I am looking for any design resources, formulae or suggestions from you people relating to this type of amplifiers. Thanks in advance.
 

HiDef

Active Member
Aug 16, 2008
543
9
28
59
The 75 mhz amp cavity would be quite physically large. Unless there is some reason to use this type of tank you'd be better off with a Pi or Pi-L network or even a strip line.

The 350 meg cavity can be found surplus on ebay and other places unless you REALLY want to build one from scratch. If so you will need plenty of finger stock.
 

doubty

Member
Sep 20, 2009
6
0
11
Thanks a lot for the reply.
I suppose 75 MHz cavity would be around 1m (lambda/4) in size. Thats ok for me. I need to learn this technology to go for higher powers.
As you said I will need lot of fingerstocks.. thats a piece of very useful information.. finger stocks can be arranged i suppose..
can you provide me anymore details regarding the design and construction?
 

Captain Kilowatt

Professional Amateur
Staff member
Apr 6, 2005
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Nova Scotia,Canada
A kilowatt on 75 MHz? That sounds like one hell of a remote control system. :LOL: Not much else going on up there except for some airport outer beacons for ILS approach systems and you do NOT want to be messing with those or glide slope markers around 335 MHz.

So why the need for such power levels on 75MHz and 350 MHz? Understanding the end use may assist in the details of how to build. Is it an amp or a transmitter? Is it modulated and if so how? AM? FM? Pulse?
 

doubty

Member
Sep 20, 2009
6
0
11
cavity tube amplifer

I am trying to participate in a particle accelerator project. My project guide had asked me to collect any info about this method. It seems we will need more than 1 kW. It is perfectly legal. we need pure sine wave and no modulation or pulsing. my project requires me to make the amplifier and match it to a 50 ohm load. At least thats what i have been told so far. I am unabled to find any proper documents, websites giving the design details of such amplifiers whereas there are plenty on lumped LC designs. I became a paid member of ARRL for one year in the hope of finding something. But I have failed to find anything useful.. my project is stuck and I have wasted a lot of money already. If anyone can help me I would be very grateful.
 

HiDef

Active Member
Aug 16, 2008
543
9
28
59
I am trying to participate in a particle accelerator project. My project guide had asked me to collect any info about this method. It seems we will need more than 1 kW. It is perfectly legal. we need pure sine wave and no modulation or pulsing. my project requires me to make the amplifier and match it to a 50 ohm load. At least thats what i have been told so far. I am unabled to find any proper documents, websites giving the design details of such amplifiers whereas there are plenty on lumped LC designs. I became a paid member of ARRL for one year in the hope of finding something. But I have failed to find anything useful.. my project is stuck and I have wasted a lot of money already. If anyone can help me I would be very grateful.

If you know anyone in IEEE there are exact peer reviewed papers which can be viewed. I did see one particle accelerator paper using google. Time to make a deal on a used TV IOT transmitter. Got 3 phase?
 

doubty

Member
Sep 20, 2009
6
0
11
My guide has access to ieee. i gave a search in google and did not find any of those papers. What keyword did you give? If possible can you give me the name/ details of the paper. I can get it downloaded. At present I have to begin work on a pentode 5CX1500A, later i can suggest IOTs as you said. And yes, I have 3- phase supply. These people have already worked on lumped component based high power amplifiers so all that infrastructure is available, but they have no previous experience on cavities.
 

HiDef

Active Member
Aug 16, 2008
543
9
28
59
Google works better when you add more information. A single or couple words won't work. Try Particle accelerator cavity power amplifier.

Also use the IEEE access for particle accelerator papers.


Check out the IOX series transmitters @

Thomson Customer Service Bulletins

There are available for the taking at many TV stations due to the analog shutdown. They are power hogs when converted to DTV compared to the newer MSDC IOT xmitters so they are considered boatanchors.

You would be looking at 480 3 phase at 225 amps service for a typical 30-40 kw out the pipe at 600 mhz.

Personally, I'd not bother with a tetrode cavity amplifier as the IOT will be the best choice for higher power and is quite a bit different in application.

What part of the country are you in?
 

doubty

Member
Sep 20, 2009
6
0
11
Hi, sorry for the delay..
i was searching google for some days.. i cudnt find a single article on how to start designing a cavity amplifier, no single formula or rule to start with.. Some of the things I'm looking for are: For 75 Mhz how big a cavity should i choose i.e. what should be the length and radius of inner and outer tubes, what material would be good, what distance and precision of movement of short would be required for good results, what type of coupler is best and where and how it must be placed for best results, what part of the coupler should i change to match it with the load etc.. Right now i have to concentrate on the 5CX1500A pentode based 1 kW amplifier.
I am from western part of India.
One more thing, can anyone here guide me to any other community group or forum where this topic would be relevant?
 

mackmobile43

Jock Supporter
Feb 11, 2008
6,700
401
0
Hi, sorry for the delay..
i was searching google for some days.. i cudnt find a single article on how to start designing a cavity amplifier, no single formula or rule to start with.. Some of the things I'm looking for are: For 75 Mhz how big a cavity should i choose i.e. what should be the length and radius of inner and outer tubes, what material would be good, what distance and precision of movement of short would be required for good results, what type of coupler is best and where and how it must be placed for best results, what part of the coupler should i change to match it with the load etc.. Right now i have to concentrate on the 5CX1500A pentode based 1 kW amplifier.
I am from western part of India.
One more thing, can anyone here guide me to any other community group or forum where this topic would be relevant?
www.qrz.com or (www.mauldroppers.com , ask for coolbreeze)
 

Slam Dunk

Member
Jul 11, 2006
79
0
16
I am trying to participate in a particle accelerator project. My project guide had asked me to collect any info about this method. It seems we will need more than 1 kW. It is perfectly legal. we need pure sine wave and no modulation or pulsing. my project requires me to make the amplifier and match it to a 50 ohm load. At least thats what i have been told so far. I am unabled to find any proper documents, websites giving the design details of such amplifiers whereas there are plenty on lumped LC designs. I became a paid member of ARRL for one year in the hope of finding something. But I have failed to find anything useful.. my project is stuck and I have wasted a lot of money already. If anyone can help me I would be very grateful.

A "Rocket Scientist" looking for "Star Wars" help on a CB/Ham message board. :unsure:

Best I can offer is, "Good Luck"!

.
 

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