Mystery Klystron Tube

[gigavolt]

A friend gave me this funky microwave device labeled "MICROWAVE OSCILLATOR 50052" "Project Physics" "DAMON".  Based on some googling of the tube, I think that it is a reflex klystron and I want to see if I can correctly power it up, but I can't find any documentation on it.  Not even the name of the tube itself.  I've only seen ones that look similar.



The device has some banana plugs coming out of it which are labeled "-250V" "-125V" and "+250V".  Then there is another pair of banana plugs which a DMM says is hooked up to the filament.  I reverse engineered the body of the device and have an OK idea of what's going on inside.

It looks like pin 8 of the tube is the reflector and the potentiometer on the body is used to adjust that voltage.  Pin 3 (labeled +250V) is actually tied to the body of the device which is why it's labeled as GND in the schematic and everything else is referenced to it.

Anybody have some more information about this tube?  Any ideas on how to power it or fun things to do with it once I get some RF from it?  I have a 1.5 kV adjustable supply, but what filament current do I use and how do I bias it with respect to everything?

[bob91343]

Scratching my head and vaguely remembering that tube from the 1950s.  It was used as a local oscillator for perhaps a radar set.  The long pin gave it away.

Unfortunately I have no information on it.

[T3sl4co1l]

Most likely 6.3V and, Idunno, 600mA or thereabouts.  Check the resistance, the cold resistance will be around, what, 1/6th of that?

I almost wonder if it was painted over in yellow, and there's a black? coat under there along with the original type number and everything.

Yeah, the coax pin was a pretty standard way to do those.  I have a couple in my collection.

Tim

[cj]

Looks like a 2K45 http://www.decadecounter.com/vta/pdf/2k45.pdf

The device you have is the transmitter from a physics demonstration kit used to show how microwaves behave. Search for "microwave physics demo" in google for more information.

CJ

[gigavolt]

Cool!  That looks like the one.  And yeah, the filament resistance is only a few ohms, so probably 6.3V.

[cj]

I noticed the link in my previous message isn't working, alternative link: https://frank.pocnet.net/sheets/150/2/2K45.pdf

CJ

[TimFox]

The Cenco school-lab unit we had in high school painted the Klystron red to remind the students that it got hot (thermally).

[CaptDon]

I don't know exactly how they wired the supplies. I would expect the
tube to be very similar to a 2k25 or 723a xband klystron. Normally
the 2k25 local oscillators had a protective cover over the assembly
because the body of the device ran at +250 to 300vdc and could be
fatal under the right conditions. The long pin sits into the waveguide
and is basically a 1/4 wave antenna. The repellor voltage is used for
tuning and if you go from maybe -50 to -150 you will find several areas
of oscillation similar in frequency, but each of these sweet spots will
have maximum output at a particular frequency and areas where it
won't have any output at all.

[cj]

Looking at the circuit diagram gigavolt made it's wired with the cover to ground and negative supplies to cathode and reflector. I expect any exposed metal including waveguide and horn antenna to be connected to ground. This makes sense if students are to operate this equipment.

In old radars the cover may well be at high voltage level and then you'll get the safety issue CaptDon mentioned.

Klystron power supplies are tricky they must supply stable high voltages with very low ripple.
Also some klystron datasheets mention the filament should be supplied with DC as well as the magnetic field from the filament may modulate the RF.

Nevertheless klystrons are fun to experiment with but care must be taken because of high voltages.
The microwave radiation from these klystrons can be dangerous. The output power may be only 40mW or so but looking directly into the waveguide should be avoided.
 
CJ
 

[mag_therm]

I do remember getting a painful shock in engineering school.
I think it was a Michelson Interferometer.
My buddy bent down to switch on the supplies. I didn't see that and was still putting the klystron cover on.

[gigavolt]

Looking at the circuit diagram gigavolt made it's wired with the cover to ground and negative supplies to cathode and reflector. I expect any exposed metal including waveguide and horn antenna to be connected to ground. This makes sense if students are to operate this equipment.

That was just an assumption I made.  The labeling on the connectors for the device say that +250V is attached to case.  But, I didn't think anybody would be crazy enough to charge it up like that.  Especially for a classroom demo with the dial on the front which looks like it is supposed to be adjusted while it's operating.  Because of that, I just changed the reference voltage so that case was ground.

I have got one of those Hspy 400V/1A supplies on its way and so hopefully I will get a chance to power it up shortly.

[cj]

Here’s one of the experiments I did last year with a reflex klystron.
I wondered if a reflex klystron could be used as (super)regenerative receiver, it turns out you can.
Here’s a picture the super regenerative receiver I made using a KS9-40D reflex klystron.
The oscilloscope shows the response of the receiver to a -80dBm sweep from 9.3GHz to 9.5GHz.