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Lee de Forest's wonderful invention

Joined
Jun 13, 2018
Messages
335
Location
Colorado, New Mexico- and now in Washington DC
#1
I received a few Private Messages asking for more historical tales of early ham radio-- this one goes back to the very beginning--:)
.

Lee de Forest was probably the first experimenter to recognize the value of thermionic technology for radio detection. He was first intrigued by seeing the flame of a gas lamp move in sync with the discharges of a spark gap transmitter. Tho he incorrectly concluded that the flame was flickering in response to the signal (it was a air pressure patterns caused by the spark that caused the flickering)-- this observation put him on the right track. His idea went further to investigate the response to electrical vibrations in a gas flame; he even applying for a patent for several radio detection devices based on Bunsen burner flames.

Later, with further experimentation he developed the vacuum tube, with its heated element for thermionic emissions- which became the basis for the modern day vacuum tube. The rest is history.
.
.

I was recently a guest lecturer in a series on the early history of radio- especially on the history of tubes- and at the conclusion I was presented with this "5 Watt Transmitting Valve" (ca. 1918.)

I was told it had come from the collection of a former British radio ham from the 1920's.

It's pretty neat, No ?.... you can plainly see the filament, surrounded by the grid, surrounded by the plate. The filament is still good, after 100 years (and I light it on a very low voltage, just enuff to get a warm glow--it sits on a shelf as a wonderful night light.)

For those that are curious, I encourage reading about de Forrest, and his wonderful discovery.

Lauri :sneaky:
.
.
 

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Joined
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241
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#3
I was wondering how much impedance mismatch vacuum tube circuits can handle versus semiconductor. Anyone familiar with them? I would guess that flash through is still very possible but vacuum tubes already deal with very large voltages...

Have a pile of vacuum tubes, I wonder if it's easier to build a QRP transmitter final with a 50C5 or a IRF510 ...
 
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#4
That's a great question, Needs. :)

I am afraid that there is really no good answer- at least if you ask me. Ask a Gen"Z"'er and of course the answer is solid state-- ask an Old Timer and.... a lot of very good stuff is still out there and its tube'd.

Me ?- my career, up to very shortly was all this cutting edge stuff-- yet as I have tried to come off in here, and professionally-- I am a "Renaissance Girl"-- I live in this multi-time-dimensional sphere- Actually, I am really a Victorian/Edwardian trapped in a 21th century gal.
Of course everyone is familiar with the chip sets available today-- I can design- and build a SSB transceiver using a single IC and the assorted audio/RF peripherals in a snap. On the other hand......


I have a DSB (double sideband) 50 MHz transmitter built by grandfather that is a marvel in tube simplicity. It starts out with a 25 Mhz input from a VXO (variable crystal oscillator) into a 6EA8. The input is an amp/buffer that feeds the second half as a doubler/driver to a pair of 6AQ5 in push pull carrier cancellation to an audio input on their screens. (Hey, can I talk this ancient Anazai radio...?) Their output feeds a 5763 final and the output is about 8 Watts. During the good years of "F" Skip my grandfather literally worked the world on 6 metre's with this little platform (tho he used it to drive a 4CX250 'after burner' - that amp is now lost to time.)
Today his aluminium chassis, open design transmitter also graces a shelf*. I leave it on (filaments only) as another novel 'night light.')
_______________________________________________
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Tubes are very forgiving- and a lot of things were possible with them. If someone wants to step back in time, look at the myriad of old boat anchors for sale at a hamfest. Pick up an old Knight-Kit T60 (yes, I have one of those- from my father.....who said-- "what in blue blazes do you want with THAT??")--- and play around with tube technology. It will add another, fascinating aspect to your hobby,---
Oh, of that I can so assure you ! :D
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Just be careful-- those things run on high voltages and their bite can be so unforgiving.......
.
.

Lauri :sneaky:

____________________________________________________________

* He wrote it up ans its in 73 Magazine--- but I can't recall the issue
 
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Messages
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CO, USA
#5
Well, I'm not too worried about the voltages, I very well respect them after working with off-line SMPS's. In any case I actually have a few tube devices: a Heathkit shortwave radio, a Westinghouse AM/FM radio, and an Eico signal generator, each appear to work fine... No AA5 radio (yet?) and nothing that transmits.

I don't have enough tubes to keep them working unfortunately though I can withstand a few failures. I did end up with a set of AA5 spares hence the possibility of using the 50C5 as a possible QRP transmitter amplifier...

And yes, all the other devices in this radio would be modern or semiconductor, of course. Not much sense using a 6AU6 or 12BA6, but if the 50C5 has no problem with inf:1 VSWR because I forgot to connect the antenna, that would be interesting...
 
Joined
Dec 22, 2013
Messages
2,824
#6
An early encounter with HV led to a preference for solid state electronics. When I was 16, I built a home brew transmitter, powered from a TV HV supply (5U4 tube rectifier). Separate chassis for each. When I first fired it up the filaments on the transmitter chassis did not light up. In my haste I grabbed BOTH chassis! It was at that instant I remembered the ground return wire was off. Threw me right across the room! I have been wary of HV ever since. Before that, I built a power oscillator with an 808 tube. It was crude, I told visitors that it was "Zarkoff Generator" I could draw sparks and arcs to a pencil lead from the plate cap. I think radio and TV reception was wiped out on my block. It was built to no other standard but to oscillate, and that it did.

I did have a neighbor call the FCC about my CB radio. I got a call from the FCC's Chicago office (where I tested for my GROL years later) asking what my station was and my steps to mitigate the problem with my neighbors 27 MHz garage door opener, poorly shielded stereo and electronic organ (All from Sears)

Still I have in my mind some sort of envelope elimination and restoration EER amplifier employing TV sweep tubes.
 
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#7
If someone wants to step back in time, look at the myriad of old boat anchors for sale at a hamfest. Pick up an old Knight-Kit T60 (yes, I have one of those- from my father.....who said-- "what in blue blazes do you want with THAT??")--- and play around with tube technology. It will add another, fascinating aspect to your hobby,---
As they say... "12 volt radios are for wimps. Real radios can kill you".

=)

I have a sizable collection of antiques. All are complete, some actually work. Highest voltage floating around in the shack is 4200 volts. No, it's NOT in a CRT.
 
Joined
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#8
While Lee DeForest's invention made modern electronics possible, if he had had his way, there would be no amateur radio. He thought the radio waves should have been the sole domain of the "legitimate workers" and that amateur experimenters were "vandals."
 
Joined
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Messages
335
Location
Colorado, New Mexico- and now in Washington DC
#10
Isn't that something ?... no B+ supply !

And I recognize that circuit- a regenerative VHF receiver- broad as a barn door, but quite sensitive. A fun evening's 'homebrew' project from the 60's....... :)

The 12EC8 was one of the last in vacuum valve technology in competition with solid state... a loosing race- but there were a few others of these low voltage designs for 12 volt automobile radios- there was no need for a high voltage supply.

Long before my time, but, oh I have seen those dinosaurs with their vibrator HV supplies.... and transmitters with Dynamotors ! :)

Lauri :sneaky:
 

ladn

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#11
Actually it's surprising what you can do with 12 volts B+ ... VHF FM receiver perhaps....
Fun bit of nostalgia! Thanks for posting.
Like Lauri said, "A fun evening's 'homebrew' project from the 60's," but probably not very practical today since the demise of Radio Shack and "real" neighborhood electronic stores. Maybe some of us oldsters and tinkerers could source the parts from our scrap box. Sourcing the parts as new from the few remaining parts houses would be a tad costly.

Long before my time, but, oh I have seen those dinosaurs with their vibrator HV supplies.... and transmitters with Dynamotors !
Before my time, too Lauri, but I've seen some vintage Motorola low band Dynamotor transceivers powered up. Some of those monsters wouldn't even fit in a modern vehicle's boot!
 
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#12
I've heard of even using common 12AX7's is possible at 12V B+ ... I've never tried however. Unfortunately due to the high impedance of tubes, the power output is very low. Definitely depends on the tube, and I suspect nuvistors and other microminiature tubes like the CK512 can handle 12V just fine. I did try 6AL5's at 12V, actually have witnessed it myself that it has rectifying action at low voltage, though I forget how much voltage drop it had.

On the other hand, I don't think a type 80 tube will rectify 12VAC. Well it may, but the power output would be so low that it's not very useful, mostly due to impedance...
 

N4GIX

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#13
Long before my time, but, oh I have seen those dinosaurs with their vibrator HV supplies.... and transmitters with Dynamotors ! :)
My very first job back in 1965-67 was as an installer for the local Motorola shop in Alexandria, VA. I suspect I got the job mainly because they needed a healthy young man to lift those antique boat anchor "mobile radios" into the trunks of the cars and route the very heavy cables under the carpet to the underside of the dashboard! The transmitter (with the dynamotor) was a separate unit from the receiver, and between the two of them didn't leave a whole lot of room for any luggage in the taxi cabs.

I joined the Army in March 1967 and eventually wound up at Ft. Gordon, GA home of the Southeastern Signal School where I graduated first in class as a proud new "Field Radio Repairman." Upon arrival at Camp Hovey, Korea and checking into the Battalion's Radio Shop, my very first assignment was stringing new telephone lines between Camp Hovey and Camp Casey... :rolleyes:
 
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Messages
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#14
I'm surprised that AC outputs from car alternators aren't common, that could be fed through a transformer and you can get the B+ voltages for tubes this way. Granted regulating this output would be tough, and would require the car to be running to use it, and all the interference from the ignition system while it's running...
 
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#15
I'm surprised that AC outputs from car alternators aren't common, that could be fed through a transformer and you can get the B+ voltages for tubes this way. Granted regulating this output would be tough, and would require the car to be running to use it, and all the interference from the ignition system while it's running...
All this vacuum tube stuff and a VHF mobile antenna question got me to dust off my copy of THE RADIO HANDBOOK by William I. Orr W6SAI (SK). One of the chapters I flipped open was about building a HV supply from a Leece-Neville 3 phase alternator.

Link here for soft copy.

http://n3ujj.com/manuals/THE RADIO HANDBOOK.pdf
 
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Messages
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#16
When did they start putting radios in cars? Yes this is before my time, though I've seen a few artifacts that there seemed to imply there have been mass produced vacuum tube radios for cars, using specifically vibrators to generate B+ (versus dynamotors and alternator AC tap offs, apparently?). The radio must be an expensive option, must be why radios are still an "expensive" option for cars even though you can get/build one for $2 or maybe less thanks to cheap clones of the Philips TDA7088...
 
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#17
Good lord, you linked to the whole damned thing!

Makes me glad for solid state. Adding an alternator for B+ voltages is clever. I built a solid state switcher for my mobile Swan 500 back when I was 16. The fixed station power supply transformer had dual primary windings. The usual 120/240 winding, and a 12v winding. Insert 12vac, and operate the radio. So, I did.

It was pretty simple. A 555 timer running at 60 cycles amplified by a bunch of 2N3055s.

All this vacuum tube stuff and a VHF mobile antenna question got me to dust off my copy of THE RADIO HANDBOOK by William I. Orr W6SAI (SK). One of the chapters I flipped open was about building a HV supply from a Leece-Neville 3 phase alternator.

Link here for soft copy.

http://n3ujj.com/manuals/THE RADIO HANDBOOK.pdf
 
Joined
Dec 22, 2013
Messages
2,824
#18
When did they start putting radios in cars? Yes this is before my time, though I've seen a few artifacts that there seemed to imply there have been mass produced vacuum tube radios for cars, using specifically vibrators to generate B+ (versus dynamotors and alternator AC tap offs, apparently?). The radio must be an expensive option, must be why radios are still an "expensive" option for cars even though you can get/build one for $2 or maybe less thanks to cheap clones of the Philips TDA7088...
The Galvin Manufacturing company probably was the first to commercially install "infotainment" in motorcars. Then they renamed themselves Motorola for obvious reasons. One of the first cars they installed a radio into caught fire.

Motorola made a gasoline heater for cars back in the late 40's . Mrs Galvins car had a prototype and it belched fire at her and then the product was recalled.

My claim to fame? When I was a toddler in Omaha, my folks had a 1947 Willys Jeep Station Wagon with the gas heater. It belched fire at ME when the car was idling in front of the house. My Dad had it disabled and the chrome control head removed. Years later I wen to the Motorola Museum (a shame it is gone) and they had that infamous product on display.

We kept that Jeep until 1967, on its second or 3rd engine and sold it to some in laws. I wonder if that car is still around. It had the classic "woody" paint style. I doubt its 4 cylinder F head engine could have powered one of those big dynamotor sets. Its vacuum powered windsheild wipers barely had any oomph.
 
Joined
Dec 22, 2013
Messages
2,824
#19
Good lord, you linked to the whole damned thing!

Makes me glad for solid state. Adding an alternator for B+ voltages is clever. I built a solid state switcher for my mobile Swan 500 back when I was 16. The fixed station power supply transformer had dual primary windings. The usual 120/240 winding, and a 12v winding. Insert 12vac, and operate the radio. So, I did.

It was pretty simple. A 555 timer running at 60 cycles amplified by a bunch of 2N3055s.
Sorry about the data dump.

You could build that solid state vibrator today with a microchip processor as the timer and two MOSFets. That plus a decoupling cap would be the entire parts count.

I remember some hybrid car radios that had tubes and two Motorola germanium transistors on the back.
 
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Messages
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Location
RLG, Fly heading 053, intercept 315 DVV
#20
I received a few Private Messages asking for more historical tales of early ham radio-- this one goes back to the very beginning--:)
.

Lee de Forest was probably the first experimenter to recognize the value of thermionic technology for radio detection. He was first intrigued by seeing the flame of a gas lamp move in sync with the discharges of a spark gap transmitter. Tho he incorrectly concluded that the flame was flickering in response to the signal (it was a air pressure patterns caused by the spark that caused the flickering)-- this observation put him on the right track. His idea went further to investigate the response to electrical vibrations in a gas flame; he even applying for a patent for several radio detection devices based on Bunsen burner flames.

Later, with further experimentation he developed the vacuum tube, with its heated element for thermionic emissions- which became the basis for the modern day vacuum tube. The rest is history.
.
.

I was recently a guest lecturer in a series on the early history of radio- especially on the history of tubes- and at the conclusion I was presented with this "5 Watt Transmitting Valve" (ca. 1918.)

I was told it had come from the collection of a former British radio ham from the 1920's.

It's pretty neat, No ?.... you can plainly see the filament, surrounded by the grid, surrounded by the plate. The filament is still good, after 100 years (and I light it on a very low voltage, just enuff to get a warm glow--it sits on a shelf as a wonderful night light.)

For those that are curious, I encourage reading about de Forrest, and his wonderful discovery.

Lauri :sneaky:
.
.

I have to wonder if thermionics can apply to cosmic rays and thermal radiation in the atmosphere? Perhaps the energy density per cubic cm is too small.

I have an idea to detect stealth using cosmic rays. I came up with it when I read archeologists are using cosmic rays to map the inside of the pyramids of Egypt.
 
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