I became an aerospace engineer (aircraft electronics) sans degree. I was motivated. I loved the stuff. I also designed the IO board that went into the World's First BBS. Helped a little with the software. CACHE Club - Chicago. Support the Revolution Buy A Computer.

Right. The grid is biased to a set positive voltage and the signal applied to it is kept small enough to not try to drive it to less than zero volts.

Thierry Dewindt so glad you liked it and it made sense to you.

When I was early in High School and onward I got a hold of the American Radio Relay League (ARRL) Manual. It was a 3 inch thick paperback full of instructions and circuits for Radio hobby and professional applications. There were tons of stories by many of the project authors, but I remember nothing about the history of Radio. I learned more about the fundamental workings of Diodes and Triodes from Kathy than from the dry, if precise, explanations --sometimes-- provided in the book. If those books contained the history of people like Armstrong, well... if only they did.

I had always wanted to build a regenerative receiver, the first project in my father's old AARL handbook, but never found the time. Then, a few years ago, I found a fully assembled Radio Shack kit for a regenerative multiband radio in a thrift store, it was called the Globemaster. Tuning it required two hands, one on the tuner and the other on the feedback control. It was necessary to adjust both simultaneously, bringing the amplifier just to oscillation, then backing it off just a bit. It was extremely sensitive and fun to use, but something like that would not be widely marketable. I hadn't heard of Armstrong's solution, thanks for sharing that information.

Is it jus' Me, or does SUPER-HET sound macho?(sexist joke/alpha male-none of the above!)

@tadonplane In English the words INVENTED and INVITED are spelled differently because they mean different things.

@@MrCuddlyable3 that was a typo, it’s fixed, thanks.

@@tadonplane8265 Well done Sir, you are a conscientious person.

That is lovely. Thanks. How old are your grandkids?

@@Kathy_Loves_Physics You"re welcome,the youngest is eight,the twins are ten, the others are twelve,fourteen and fifteen.I have computers,chemistry,and physics labs all over the place.Your videos are inspirational to them all.

@@jamespowell1442 Wow, you sound like a fantastic grandfather. I made these videos for adults (or maybe advanced teens) so I am surprised that kids 8-15 can understand it, they must be super smart like you. My oldest child is 6, maybe I should start showing her the videos? Cheers, Kathy

@@Kathy_Loves_Physics Do basic math with applications first ,so you show how important math is to science,then show some computer basics,house old appliances that use electricity then show your videos,the discourse between you and your child will bring you closer to each other.Good luck!!

That is amazing

You where just making a sensitive VTVM with enormous high input impedance.. once you just could "smell" volts

You can repeat this with modern components, any n-channel FET instead of a vacuum tube

Glad you liked it but don't keep my videos on my computer as they would take too much room so I can't give you them to download, sorry. I have also become a HUGE Armstrong fan as well. (but his story ends so sadly)

@@Kathy_Loves_Physics Very true. I build and restore old time radios, regenerative and superregenerative recievers are very intriguing.

Thanks, so nice of you to comment on so many videos!

Thank you!

Jack D. Ripper awww thanks Jack. 😊

Jack D. Ripper I just found out that bated and abated are two forms of the same word!

I should use it more often

Armstrong was the goat of radio.

I don’t know, he was amazing and delightful. Also, he wrote an autobiography that I really enjoyed and it’s free on the web.

With a tragic end

You forgot the "Reflex" receiver. A very clever idea where the signal was sent through the active device twice - once at radio frequencies and once at audio frequencies. LC filters routed the signals through the correct path. It basically gave the performance of 2 tubes with the costs of only one and without the disadvantages of the (super)regenerative circuit.

Such a good book.

Capacitors were seen as literally 'condensing static charges' in operation. This mistaken notion was driven by countless early experiments with Leyden 'gathering' static electricity.

i’m so lucky and so much of the stuff not just old scientific papers but also old radio magazines have been digitized and I can just find it from my computer at home.

@@Kathy_Loves_Physics Excellent. Thanks a lot

One of the best lines in history

Marconi in Cornwall UK?

It’s true that his middle name was Howard but his niece called him uncle Howard, and he was referred to by his middle name in a well researched biography called “Empire of air” and he signed all his patents with his initials so I figured that he went by his middle name.

The feedback circuit's full name is the regenerative feedback circuit. This isn't feedback like you have on a microphone. It refers to ,'feeding back' part of the output into the input. This causes signal amplification bc the signals are phased in such a way as the amplitude ( volume) increases.

Also an EE here. The secret sauce is in how MUCH positive feedback you apply. Just a tiny bit can give a big boost in performance if you are limited in the number and gain of active devices. You are correct that too much positive feedback will result in the problems you mention. Think of a public address system. When a sound is fed into the microphone (assuming the microphone is not isolated from the loudspeakers) some of the sound from the loudspeakers will reach the microphone "in phase" depending on the frequency, path length, room characteristics, etc. If the "in phase" sound is low enough in amplitude at the microphone it will not cause oscillation even though it is in phase (positive) feedback. The critical factor is "loop gain". A PA system with microphone and speakers isolated from one another has a loop gain of zero at all frequencies. As you decrease the isolation between the mic and speakers (or increase the gain of the PA amplifier) the loop gain at some frequency where the feedback to the microphone is in phase will increase - but the system will be stable IF the loop gain is significantly less than 1.0. As you approach a loop gain of 1.0 the system will become less stable. It won't break into unprovoked oscillation but it will start to "ring" like a bell. A transient sound into the microphone will produce a damped tail of sound from the speakers at the frequency where the maximum amount of in phase sound is applied to the microphone. If you continue to decrease the isolation between the mic and speakers (or increase the amplifier gain) the loop gain will eventually exceed 1.0 and the fun will begin with all of the problems you mention. About 40 years ago I was working as an EE for the Canadian National Research Council in Ottawa mainly designing and building electronic equipment for the scientists to use in their research. The building I was in (100 Sussex Dr. in Ottawa) had a beautiful auditorium. I was tagged to look after the sound system in the auditorium as I was the "electronics guy". The amplifier was very interesting. As I recall it was a commercial product manufactured in Britain but I can't remember the brand name now. It had a switch to turn on "feedback suppression" and it worked by shifting the frequency of the sound signal being fed into the amplifier by a few cycles. Any sound from the speakers that arrived back at the microphone in phase couldn't build up to audible feedback because after a few round trips of the loop it would slide off the frequency where the feedback was positive and the loop gain was more than 1.0. The scheme actually worked quite well. If you opened the gain wide with the feedback suppression switch turned on it simply would not under any circumstances build up into a flat out saturated clipping oscillation. It would sort of oscillate with a warbling sound but it was fairly quiet and nowhere near saturating the output stage. In a way it was a bit like Armstrong's super-regenerative circuit where the loop gain exceeds 1.0 but the resulting oscillation is quenched at an ultrasonic rate. I hope the above helps explain how there can be positive feedback in an amplifier without catastrophic results. These days active devices are readily available, inexpensive, have high gain, and low power usage so there isn't much incentive to derive maximum performance from the minimum number of active devices in today's designs. This was not the case in the early days of electronics! For another interesting method of getting maximum performance from the minimum number of devices check out the "Reflex" radio receiver circuit. Most people have never heard of it, but it was another very clever idea.

@@Vincent_Sullivan There was a technique called neutralization, also using positive FB to increase gain at higher frequency to avoid roll-off. They used the inverted output, added some more delay such that it was in phase again. Not sure what that did to the medium frequencies, maybe it worked out because their phase wasn't delayed enough.

​@@Vincent_Sullivan I have done the math now and found that the loop amplification can be infinite if the amplifier has an amplification >1.0 If the gain is 1.1x and the FB is +0.9 the loop gain is 11x. Increase the FB just a bit and the loop gain explodes to infinity. I found that this is how cheap 50MHz BJT FM amps work. They simply feed an insane current into the base.

Who are you talking about? I’d love to learn more