Modern green LEDs will light up with just a few uA running through the device. Easily to check: such a LED in series with a 470k resistor will light up when holding one end with fingers and other to the "hot" end of AC line. With RF that won't be different, so any coupling coil delivering enough voltage (easy with tube circuits) will light up the LED.
OK. in the pic seems metalic. Bad mine.
Wonderful. The absolute value of the plate current of a tuned Class C like your futherly pentode isn't crittical. The goal is to find the current dip as I mentioned earlier here.
200pF is OK.
Spectacoular! Yes, hook them and if you want, the screen and plate circuit too but keep it without Ebb (power suply) until being sure suffient negative bias is obtained. Class C tuned amplifiers get their bias thanks to rectifying the incoming signal. As the cathode is grounded, positive going signals are rectified in the cathode-grid circuit acting as a diode. Grid attracts electrons when positive respect to cathode and stores it in your C5. When signal goes negative it adds to the negative voltage stored in C5 carrying pentode into cutoff. Thus when grid was positive a large and thin spike of current flows in plate and screen. This current generates a voltage in the tuned plate circuit close to a sine wave. Thus, this is esentially different for a Class A audio: plate current and voltage obeys grid signal. Class C doesn't. Plate voltage is always sine (at resonance) while current is a spike.
Tuned class C are similar to a mass attached at the end of a spring. If you keep the mass and the spring dancing up and downwards, at some time the energy is lost thanks to air viscosity. But if in every same moment (say when wheight is in the upper position) you hit it downward again, oscillation mantains or ever grows depending on the energy you gave to it.
Thus, pentode stimulates once a cycle the tuned circuit to mantain current in it. This is why current and voltage differs each other. But curiously, the current flowing through inductor and capacitor alone ARE sine like.
Enjoy the hobbie.
A quick update... I added just the R3 and C5 and voltage on pentode's control grid is only -3,7v, voltage on the triode's grid is -2v....
Just to be sure please look at that schematic that I had drawed and confirm if c5 and r3 gets connected to the RFC1 & the triode's cathode (8) before getting wired in between the c1 & c2... (cross on the schematic)
I didn't connect anything to the pentode's screen or plate.
Ok, will need to buy the caps tomorrow. I did one quick test tho... I connected another 100pf in parallel and voltage of pentodes grid felt a bit as expected... to 3.0v, so there is a feedback.... will report when I change the cap.
I bought a bunch from eBay. They're so bright I use them in clip indicators to see clipping starting at THD 100 ppm. These are the ones performing that way: used antiparallel with proper series resistor, a much improved replacement for the aged neon bulb. Emphasis is on 10,000 mcd and higher is better. When buying from a shop, test with 9V battery plus 1 meg resistor.
10,000mcd green LED
One more acclaration. You must not confuse the band or frequency of emision of a TX with the way it is modulated.
You may have a 100MHz transmitter modulated in AMPLITUDE and a 1MHz TX modulated in FREQUENCY. Commercially they are assigned as almost all know: AM for 500 to 1600KHz and FM for 88 to 108MHz. But you can build an 1400KHz FM modulated and other at 90.7MHz amplitude modulated. At both cases, it will be difficult anyone can listen to your emmision properly, but this is other problem. I suggest search in any radio book or web page and fix this concepts. IMHO. 🤔
You may have a 100MHz transmitter modulated in AMPLITUDE and a 1MHz TX modulated in FREQUENCY. Commercially they are assigned as almost all know: AM for 500 to 1600KHz and FM for 88 to 108MHz. But you can build an 1400KHz FM modulated and other at 90.7MHz amplitude modulated. At both cases, it will be difficult anyone can listen to your emmision properly, but this is other problem. I suggest search in any radio book or web page and fix this concepts. IMHO. 🤔
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Ok will do some research on that.One more acclaration. You must not confuse the band or frequency of emision of a TX with the way it is modulated.
You may have a 100MHz transmitter modulated in AMPLITUDE and a 1MHz TX modulated in FREQUENCY. Commercially they are assigned as almost all know: AM for 500 to 1600KHz and FM for 88 to 108MHz. But you can build an 1400KHz FM modulated and other at 90.7MHz amplitude modulated. At both cases, it will be difficult anyone can listen to your emmision properly, but this is other problem. I suggest search in any radio book or web page and fix this concepts. IMHO. 🤔
EDIT: I had actually read about this as it was covered in many "How AM works" articles, if we are thinking of the same thing:
Frequency modulation for carrier signal and then it gets amplitude modulated as "sound gets injected".
This is it right?
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The carrier is only a medium to carry the wanted signal across long distances that the signal alone can't do. As all sine wave you have 3 parameters: amplitude, frequency and phase. One or more can be modified by the modulation signal accoring to the method used. Amplitude and frequency are the most known but phase exists too. It behaves a bit similar way to frequency modulation but has lack of low frequencies when listened on an FM receiver.
Ok....
I replaced c1 with 22pf, but voltage at pentode's grid is -3v... Did you mean c5? Both are grid to the cathode, it's just that c1 is from triode to triode and c5 is from pentode's grid to triode's cathode...
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