Here is an anecdotal story. Your mileage (or kilometers) may differ of course...
Near the middle of the last century I was serving a four-year term of enlistment in the U.S. Air Force. Life was boring for a single airman stationed at a snowy, isolated, post in the northern peninsula of Michigan. When I was offered an opportunity by my first sergeant to join the local base amateur radio club and study for a Novice-class amateur radio license, I eagerly accepted. A few weeks later, while "practicing" receiving Morse code in a class held at the clubhouse, I was surprised to be informed that I had passed the 5 word-per-minute Morse code test! I didn't even know I was being tested... nor did any of the other students in the class know when they were being "tested," lest they fill up with dread and fail to copy the code. So we all passed our code tests, and we all passed the written "theory" test, and the volunteer examiner sent the results off to the FCC. Some time later (probably no longer than a month but it seemed like forever) we received our "tickets," a printed paper license authorizing each of us to own and operate a radio station in the amateur radio service. We were now Hams!
I had a LOT of time on my hands during off-duty hours, and I was anxious to get started in amateur radio. I couldn't afford a Collins "rig" which was the "top-of-the-line" equipment in 1966, so I settled for an almost "look alike" Heathkit SB-300 receiver kit:
I was barely able to afford this kit on my A2C monthly salary. And there was no money left over to purchase a transmitter. So, after putting the receiver kit together, and with the help of a few friends (and permission from the first sergeant) we erected an 80m dipole antenna about ten feet above and parallel with the gravel-and-tar roof of our barracks. I found a spool of "practically new" coaxial cable tucked away in a corner of our Armament and Electronics (A&E) maintenance shop. Using an oscilloscope and a pulse generator, along with a variable 100 ohm potentiometer connected across one end of the coax, I determined that the coaxial cable characteristic impedance was 50Ω. Voila! My first sergeant determined that the spool of coax was "surplus" to our shop's current needs and allowed me to remove it to the barracks and install it between my ground-floor room and the roof antenna some three stories higher. So after a few months of labor I was now "on the air" as a short-wave listener (SWL) and could practice receiving CW transmissions by real amateur radio operators while I built a Novice transmitter.
I devoured the only issue of The Radio Amateur's Handbook (an ARRL yearly publication) that I had, reading it from cover-to-cover while drawing up schematics of various transmitter options. Back in those days, Novice class licenses were limited to transmitting with only 75 watts of input power to the "final" output tube. And the dipole antenna I had erected was useful only on the 80m amateur radio band, where a small slice of spectrum was allocated for Novice operators. Allocated, not reserved: any other amateur could use the same slice of spectrum but Novice operators could only operate in "their" slice. Still, it was enough to make contacts with other amateurs, including some novices, and become proficient in receiving and transmitting Morse code. Now all I needed was a transmitter and a telegraph key. And maybe some earphones. And an SWR bridge. And maybe a grid-dip meter for pruning the dipole to the proper length for resonance in the 80m NOVICE band... Geez, this is becoming an expensive hobby.
Besides spectrum (band) limitations and power limitations, Novice-class operators were also "rock-bound" to fixed frequencies, selected by whatever quartz crystals one could afford to buy. I could live with that, transmitting on one frequency while listening on another slightly different frequency, changing crystals if necessary to avoid QRM (interference) from more powerful stations who wanted to park their transmissions at or near the frequency I was using. I was able to purchase, scrounge, or otherwise acquire about a half dozen quartz crystals for the 80m Novice band (3.525 to 3.600 MHz) and by the winter of 1966 had finished construction of my very own Novice transmitter and a separate power supply for it. I wish I had taken and preserved pictures of this "rig" because I was really proud of my work. The RF power section was fully enclosed inside a mesh cage salvaged from the high voltage section of a junk TV. I used an RCA 6146B beam-power pentode biased for Class C operation driving a pi-network load. A separate RF oscillator tube and full break-in (QSK) keyer with envelope-shaping network, to eliminate key "chirps" or "clicks" drove the "final" to 75 watts input power. I spent all my free time that whole winter "on the air" practicing Morse code and "rag chewing" with those Hams who enjoyed it.
The dipole was not oriented in a very favorable direction. IIRC, the wire ran east and west along the top of the barracks, meaning the antenna lobes were oriented north and south. Not much was north of Kincheloe AFB, MI and very few stations were directly south either. Still, I managed to obtain contacts and held conversations (QSOs) with many stations until my enlistment expired in May 1967. During the time I was operating "on the air" I learned a few "tricks and tips" from other Hams. One of these seemed novel and simple to apply: use an ordinary, wood-encased, sharpened #2 lead pencil to test your RF "tank circuit" for the presence of RF, drawing a short, hissy, arc from the tank coil to the pencil point while holding the body of the pencil between thumb and forefinger. Worked like a charm on my little transmitter, although I still used a small neon lamp connected to a single loop of wire as a visual indicator.
After leaving the Air Force, I managed to get a job as an electronics technician at a local university. Lots of opportunities to discover new things electronical as well as optical, chemical, and other branches of science. One day I was asked to help out with troubleshooting an RF induction heater. This little beastie operated at about 450 kHz, which is near the frequencies that Tesla coils generally resonante. It used a water-cooled power triode as an RF oscillator to drive ten turns or so of copper tubing wound around a hollow nickel "susceptor." The copper tubing had cooling water flowing through it because the nickel susceptor became white hot (Incandescent) during induction heater operation. Except this day it wasn't doing that. I suspected the power oscillator had quit oscillating and so I pulled out a #2 lead pencil to test that theory, a 'la amateur radio practice.
I was still pretty new at working around high-powered electronics, so I gingerly held the pencil at one end with the metal ferrule holding the eraser grasped between my thumb and forefinger. I carefully approached the tank circuit, attempting to draw a small arc if it were operating. When the pencil point came within about a half-inch of the tank coil a fat, sizzling, arc jumped across the gap. Another arc formed between my fingers, thumb, and pencil. All this happened very quickly and the result was I immediately dropped the pencil. Unfortunately the damage had already been done. I pin-point sized wound pierced my thumb and charred the flesh around the area where the arc occurred. It was quite painful, but more importantly, it took almost a month to heal.
Apparently the flesh was cauterized internally as well as externally, prolonging the healing process.
I learned a valuable lesson from this (non-fatal) experience: use proper test equipment instead of my valuable body to test electronics. I do remember when I was just a kid that a neighborhood radio-tv repairman, who also happened to be a licensed radio amateur, showed me how he tested for the presence of AC in his basement workshop, cum ham-shack, with knob-and-post wiring by carefully bridging two bare wires with thumb and forefinger. Seemed to me like a dumb thing to do, standing on a dirt floor in a damp basement, but the idea must have stuck in my head somewhere for me to try a similar stunt with a 50 kW RF induction heater.
Do be careful messin' aroun' with Tesla coils, even if they are built with so-called slayer exciters and operate from 9V dry cell batteries instead of from mains power. Believe me, you are NOT ready for a mains powered Tesla coil yet.