Continuous output magnetron possible?

Thread Starter

kunkle11

Joined Mar 5, 2016
3
Hi all. First post here. I have very limited electronics knowledge so far. Working on plasma research project. Main issue is the pulsed nature of my magnetron to ionize plasma. I already have a 700W magnetron from an oven running satisfactorily- getting plenty of output into the vacuum chamber. If possible, I need to convert the pulsed microwave output to continuous.
 

GopherT

Joined Nov 23, 2012
8,009
Hi all. First post here. I have very limited electronics knowledge so far. Working on plasma research project. Main issue is the pulsed nature of my magnetron to ionize plasma. I already have a 700W magnetron from an oven running satisfactorily- getting plenty of output into the vacuum chamber. If possible, I need to convert the pulsed microwave output to continuous.
Let me put my mind reading cap on and visualize the schematic from the model number of the microwave you are thinking about. Just a minute, concentrate on that model number really hard, I can see it better that way...
 

ian field

Joined Oct 27, 2012
6,536
Hi all. First post here. I have very limited electronics knowledge so far. Working on plasma research project. Main issue is the pulsed nature of my magnetron to ionize plasma. I already have a 700W magnetron from an oven running satisfactorily- getting plenty of output into the vacuum chamber. If possible, I need to convert the pulsed microwave output to continuous.
Most likely the bottom line is dissipation.

Pulse operation is usually at a much higher power level than you can get away with continuous.
 

Thread Starter

kunkle11

Joined Mar 5, 2016
3
Off to a really bad start here. Hit some wrong button and it posted when I'd barely written anything, and then it dumped my entire post when I tried to edit it because I took longer than 10 min. Now I don't see any way to edit it. Sorry. Let me try again:
Main issue is the pulsed nature of my magnetron to ionize plasma. I already have a 700W magnetron from an oven running satisfactorily- getting plenty of output into the vacuum chamber. If possible, I need to convert the pulsed microwave output to continuous.
Don't know the model of the oven anymore- it's long gone. FWIW, the transformer is iron core with a doubler circuit using a .75uf 2100V cap.
After exhausting google and searching this forum, here's what I came up with. Convert wall outlet to continuous 120V DC with a full wave bridge rectifier, then a 680uf cap in parallel. I also need continuous 120V DC for some tungsten emitters, so If a different cap would work better- let me know.
A reply to an old post on this forum suggested taking 2 MOTs and wiring their secondary output in series to get from 2k to 4kV. I always thought this was a no-no, but no one rebuked that reply either. So, can I take the continuous output 120V DC from the above circuit and feed that into 2 MOTs in series, then to the magnetron? Seems to easy to be true. Thanks for any help.
 

WBahn

Joined Mar 31, 2012
29,976
The output of a full-wave rectifier with a smoothing cap will be about 170 VDC without any load. What it will be with a load will depend on your cap and the load. The average voltage will drop and the ripple will increase.
 

Thread Starter

kunkle11

Joined Mar 5, 2016
3
The output of a full-wave rectifier with a smoothing cap will be about 170 VDC without any load. What it will be with a load will depend on your cap and the load. The average voltage will drop and the ripple will increase.
As far as the emitters circuit goes, they will use about 150W. Any suggestions to keep the ripple at minimum at that rate? Thanks.
 

WBahn

Joined Mar 31, 2012
29,976
You need to convert that into an average current draw from the DC supply (150 W draw does not translate directly to current if, for no other reason, the efficiencies involved).

Can your circuit handle 170 V DC?

If you want 120 VDC, then you would probably be well-served by regulating the voltage to 120 VDC. Doing so would also drastically reduce the ripple voltage.
 

tcmtech

Joined Nov 4, 2013
2,867
So, can I take the continuous output 120V DC from the above circuit and feed that into 2 MOTs in series, then to the magnetron? Seems to easy to be true. Thanks for any help.
Do you think you can run DC through a AC transformer? o_O

More than likely the pulsing is coming from the simple half wave charge pump type voltage multiplier circuit that is use to power the magnetron. Adding a few more diodes and a capacitor or two more would convert that to a full wave charge pump greatly reducing the overall voltage fluctuations that the magnetron is seeing now.
 

Lestraveled

Joined May 19, 2014
1,946
First, good luck. That tube was not designed to run in CW mode. But since it was cheap, lets see what it can do.

Be careful, the voltages and RF power outputs are damaging if not deadly.

You will have to run the tube at a reduced voltage. What that voltage is, I don't know. Start low and slowly increase.

What equipment do you have to detect and measure the RF output of the tube?? If you do not have equipment to make these measurements, stop until you do have the equipment.

You will need to measure the power supply current as you increase voltage. Do this safely.

If it does start to oscillate, the frequency will probably not be at the normal pulsed frequency.

This is not a casual experiment. It is dangerous. If there is a crack in the waveguide it will paint you with RF energy. Your eyes are the most easily damaged.
 

Ramussons

Joined May 3, 2013
1,404
As far as I can remember, the working principle of a magnetron is Pulsed Mode. I would be very thankful if someone here can explain how a magnetron can operate in a continous mode :confused:
 

Deleted member 115935

Joined Dec 31, 1969
0
wow,

Please be careful.
Worked for years in radar design works,

these things kill.
the electricity is the least of your worry, the RF is the thing. Ensure your lab has RF radiation detectors, that work. Also make certain you have plenty of kill switches around, that others know about and can always be easily hit...

and don't allow any distractions, that friend that pops in with the coffee and distracts you as you erradiate your eyes, is a lousy excuse to go blind. ... ( seen it ... )
The health and safety paper work is amazing.

ok back to the questions.

Magnetrons can be run continuous or pulsed,
As mentioned above its thermal dissipation that can catch you out.

CW magnatorns of more than a few watts tend to have water cooling for a reason.
They are about 60 % efficient, depending upon the load VSWR... so if you have a 700 watt output, your magnatron is going to dissipate about 500 watts . Pulsed at about 10 % , thats 50 watts, if you up it to 100 % thats a fair amount of dissipation.

Wiring outputs of transformer in series, quiet normal,
You can get many transformers that have multiple secondary windings, and depending how you connect them depends what voltage out you get. Using two separate transformers, primaries wired in parallel and secondary in series is just the same, if you get the phases correct. Get it wrong and you will know about it.

I assume you know about coronal discharges, and HV cables over regular cables. If you have to ask. STOP NOW. 2 Kv at 10 mA will kill at a distance, even through plastic 'insulators' . Please remember that HV capacitors have a hidded kick, you discharge them, and leave alone and a few moments later they have a charge back across them. HV capacitors that can be accessed , like on experimental gear should have a fail safe dump circuit across them.
 

Techohead

Joined Nov 23, 2020
11
As far as I can remember, the working principle of a magnetron is Pulsed Mode. I would be very thankful if someone here can explain how a magnetron can operate in a continuous mode :confused:
There is no reason they can't work in continuous mode. I have a copy of an inverter u~ oven cct that has a capacitor filtered continuous o/p. In a 50Hz or 60Hz cct., 1/2 wave is convenient for the voltage doubler cct.
 

Techohead

Joined Nov 23, 2020
11
I
Hi all. First post here. I have very limited electronics knowledge so far. Working on plasma research project. Main issue is the pulsed nature of my magnetron to ionize plasma. I already have a 700W magnetron from an oven running satisfactorily- getting plenty of output into the vacuum chamber. If possible, I need to convert the pulsed microwave output to continuous.
Hi all. First post here. I have very limited electronics knowledge so far. Working on plasma research project. Main issue is the pulsed nature of my magnetron to ionize plasma. I already have a 700W magnetron from an oven running satisfactorily- getting plenty of output into the vacuum chamber. If possible, I need to convert the pulsed microwave output to continuous.
Hi all. First post here. I have very limited electronics knowledge so far. Working on plasma research project. Main issue is the pulsed nature of my magnetron to ionize plasma. I already have a 700W magnetron from an oven running satisfactorily- getting plenty of output into the vacuum chamber. If possible, I need to convert the pulsed microwave output to continuous.
I would suggest taking the innards out of an inverter microwave if you want continuous power. It will be far easier & safer. The voltage across the magnetron in a 50Hz or 60Hz cct. is a 0 to -4kV square wave and the current through the voltage doubler capacitor is sinusoidal. You would need another HV diode and a large 4kV capacitor or several 2.1kV capacitors in series/parallel to filter it properly, because magnetrons act like 4kV zeners. They don't even start to conduct until the voltage is about 3.9kV, and conduct heavily at 4kV, so you would need a lot of filtering.
 

Attachments

MisterBill2

Joined Jan 23, 2018
18,167
The output of a full-wave rectifier with a smoothing cap will be about 170 VDC without any load. What it will be with a load will depend on your cap and the load. The average voltage will drop and the ripple will increase.
How do you get 170 volts DC from a 2000 volt transformer?? Are you responding to the wrong thread????
 

MisterBill2

Joined Jan 23, 2018
18,167
Certainly the output from a non filtered half wave rectifier will be pulses. I saw no mention of the apparent pulsing rate so I can guess that it is at the line frequency. So a second transformer and rectifier to supply the other half oof the wave would be part of a solution.

It seems that most of the oven transfomers have one end of the secondary grounded, and none of them can withstand a voltage twice as high.
BUT it would make real sense to obtain an actual high voltage transformer rated for full wave bridge service and thus having adequate insuklation and being designed for continuous operation. And also required will be some actual filter capacitors to hold up the voltage so that the energy will not be variable. Research the design ogf high voltage supplies for amateur radio linear amplifiers and you will find lots of information. AND finding such a supply, used or surplus, is also an option.
 

WBahn

Joined Mar 31, 2012
29,976
How do you get 170 volts DC from a 2000 volt transformer?? Are you responding to the wrong thread????
Well, it's possible. Since the reply was written nearly five years ago it's hard to remember. But looking at the post immediately before my reply makes me think not, since it says, "Convert wall outlet to continuous 120V DC with a full wave bridge rectifier, then a 680uf cap in parallel." and I responded with, "The output of a full-wave rectifier with a smoothing cap will be about 170 VDC without any load."
 

MisterBill2

Joined Jan 23, 2018
18,167
Well, it's possible. Since the reply was written nearly five years ago it's hard to remember. But looking at the post immediately before my reply makes me think not, since it says, "Convert wall outlet to continuous 120V DC with a full wave bridge rectifier, then a 680uf cap in parallel." and I responded with, "The output of a full-wave rectifier with a smoothing cap will be about 170 VDC without any load."
This question was about the output od a microwave magnetron transformer, usually 2000 volts AC.
 

WBahn

Joined Mar 31, 2012
29,976
This question was about the output od a microwave magnetron transformer, usually 2000 volts AC.
So? Does that mean that when the TS talks about their internet searches leading them to conclude that they need to convert the power from the wall outlet to 120 VDC using a full wave bridge rectifier and a 680 uF cap in parallel that this error in their understanding should be ignored?
 

MisterBill2

Joined Jan 23, 2018
18,167
So? Does that mean that when the TS talks about their internet searches leading them to conclude that they need to convert the power from the wall outlet to 120 VDC using a full wave bridge rectifier and a 680 uF cap in parallel that this error in their understanding should be ignored?
Clearly you are referencing a quite different thread. This thread is about the high voltage thread for a magnetron plasma generator power supply, which uses a high voltage transformer.
 
Top