A neat little widget: homemade solid state amplifying device...

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A neat little widget: homemade solid state amplifying device...

Post by Ragwire on Sun May 17, 2015 12:11 am

...That is, the amplifier circuit (used for an oscillator for testing, in this case) is homemade, but so is the actual active device:

Took some patience, but I built this "zinc negative resistance oscillator" after Nyle Steiner's design. (sparkbangbuzz.com)
This is a homemade tunnel diode amplifying device that works well for radio frequencies well into the higher frequencies...sort of like a 2 terminal transistor, in a way.
I found the piece that worked best was a strip of galvanized sheet steel that was scortched pretty fast in a hot flame until white hot sparks were jumping, and quenched in water while still red hot. The catswhisker is just a piece or 22 gauge copper wire cut at an angle for a semi-sharp point. I pressed that point through a small disk of plastic so it stuck through about 1/8", and put some Duct Seal on the back of the disc for a little weight. This way I can pick up the whisker by its little connector wire (a single copper strand from and old stranded lamp cord) and set the tip in different places--or drag it gently--until I got a bit of oscillation on the scope (more than the damped wave you get when it makes and breaks contact). Then the potentiometer was adjusted for stable oscillation.
I changed the power supply slightly from Mr. Steiner's design to give more current control. I had no luck with the website's exact power supply design.

I haven't attempted to use it for a crystal radio RF pre-amplifier or regenerative receiver design yet, because I do not have a crystal radio set up right now, but I will probably mess with that later on. If it oscillated, it has gain, so it should work fine if adjusted properly.

By the way, I found Steiner's zinc detector diodes both easy to make (much easier than the oscillator) and excellent performers.







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Re: A neat little widget: homemade solid state amplifying device...

Post by Ragwire on Thu May 28, 2015 1:28 pm

A more refined version.
I wanted to see how well this could amplify a modulated RF signal, so I set turned the voltage on this one just below the oscillation point and injected a tone modulated signal from the signal generator which was tuned to the same frequency as the resonant circuit, and played with the voltage level potentiometer a bit. I also cut the power and looked ate the signal output with the ZNO device both in circuit and bypassed. The scope clearly showed an increase of several times the input signal level when the batteries were connected.
I can see where this really could give a big signal boost to a crystal radio receiver.

The zinc plate and wire are different specimens than the previous unit posted here. I just made some new ones for the little adjustable holder I made.

Still no luck on the point contact transistor or homebrew tubes yet...but this device seems to work well for anything I would likely use the those for anyway.

cheers
Rob



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Re: A neat little widget: homemade solid state amplifying device...

Post by 75X11 on Thu May 28, 2015 2:52 pm

I am at a loss to figure out how I missed this thread when it first appeared. That is a quite impressive project and congratulations on such an outcome! I wish there were still some of the good old electronics magazines around so you could get the publishing credit you deserve.
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Re: A neat little widget: homemade solid state amplifying device...

Post by Ragwire on Thu May 28, 2015 10:51 pm

Thanks for the kind words...it's not my idea though. I'm just dorking around the old workshop seeing if I can brew my own solid state amplifier like Nyle Steiner and some others have done. Apparently, I can! A lot easier than making even a crude vacuum tube, too... Laughing

I forgot to mention, the peak to peak voltage in this example is likely about 6-8 volts at 800 kHz. Pretty strong. I can pick it up on an AM receiver as far as I tried. When I tuned it past 1 MHz, the oscillator died and I had to readjust the potentiometer a little to start it back up. They are impedance sensitive and sometimes need voltage adjustment for changing frequencies or loads. I guess it's the foxhole radio equivalent of an amplifier...you have to mess with it. But once it's adjusted to be relatively stable, I can kill power to it (in oscillation mode) and it will start up when I power it back up. When I have the voltage set lower so it won't oscillate itself, then any RF signal I apply pretty much amplifies with little if any further adjustment.

cheers
Rob
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Re: A neat little widget: homemade solid state amplifying device...

Post by 75X11 on Fri May 29, 2015 12:13 am

I used to do testing on diode voltage multipliers used for a "blanking" voltage potential for traveling wave tube amplifiers. I made up a circuit using that process to step up an audio signal to control a call check recorder.
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Re: A neat little widget: homemade solid state amplifying device...

Post by Ragwire on Fri May 29, 2015 9:00 pm

I never have worked with a traveling wave tube amplifier...is that the one that bends the electron beam with the input signal?

Just a little update, too, I got it working as a pre-amp for my crappy crystal radio this morning. Far from optimized...I just slapped something together...but it sure did double the volume and I know it can do better when I match impedance to the radio.

cheers
Rob
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Re: A neat little widget: homemade solid state amplifying device...

Post by 75X11 on Fri May 29, 2015 9:06 pm

It works by velocity modulation somewhat like a klystron tube or a ruby laser. The signal is injected into an oscillating beam. It was used as the final uplink amplifier in an airborne video transmission system to transmit real time video of the type shown during Operation Desert Storm.
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Re: A neat little widget: homemade solid state amplifying device...

Post by Ragwire on Mon Jun 01, 2015 9:58 pm

You lost me there...but that's OK. I am not an EE. LOL

cheers
Rob
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Re: A neat little widget: homemade solid state amplifying device...

Post by Ragwire on Sun Jun 21, 2015 7:57 am

Adding a note here: The metal working, of course, was done outside and with appropriate protection from heat, sparks, and fumes. Zinc fumes, I have read, are not good to breath.
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