Hi, I don't know if I am posting this in its place. I am designing a FM 1 Tube Rege. 88-108 Mhzs. receiver, tuning by varactor. I have finished my diagram, but I have some doubts anyway. There is a clear lack of this type (varactor) operate receiver in the Web. I am wondering if my design is going to work or close to. Here include my schematic. Any comment!. Thanks a lot.

 

Welcome to AAC!

I don’t see how this is a regenerative radio receiver.
I don’t see how this is an FM receiver. I looks like an AM receiver to me.

 

I have finished my diagram, but I have some doubts anyway. There is a clear lack of this type (varactor) operate receiver in the Web.

1N4007
AI: While the 1N4007 is a rectifier diode and not specifically designed as a varactor (also known as a varicap or tuning diode),
it can be used in some applications as a substitute due to its voltage-dependent junction capacitance.
Varactors are designed for this purpose, with careful doping to optimize capacitance variation with voltage, while the 1N4007's primary function is rectification.

 

Hello,

What capacity range do you need?
This site has a lot of varicaps:
https://www.rf-microwave.com/en/varicap-varactor-diodes/434/

Bertus

 

I need 1 up to 22pF, but I can use a BB205 varicap diode or a regular 1N4007, but I doubt this circuit could work 100% as is. It's a critical working tank circuit, and I would like accomplish this idea. I know it looks like an AM design, but I have not farther information because it's an unusual diy diagram. I don't like the FM Chinese ones neither, of course the are cheap, but I am trying to use TV tubes instead as PCF80, for instance, besides, I try to avoid just using Variable Capacitor and these type of tubes are very common here in Europe. Thanks in advance.

 

I don’t see how this is a regenerative radio receiver.
I don’t see how this is an FM receiver. I looks like an AM receiver to me.

It's not obvious but it actually should receive and demodulate the FM signal.
You tune it slight off center of the station's frequency so it is on the slope of the receiver's resonant frequency.
This gives a variation in the audio output as the station's frequency is modulated by its audio.

Here (schematic below) is a similar FM 1-tube receiver I built way back in the 60's (actually still have it) ,which was tuned by a dual 15pF variable mechanical capacitor (and notice the selenium rectifier).
Not great sensitivity, but I could pull in local stations with just a simple T dipole antenna made from some 300Ω twin-lead.
(Of course, no stereo).

 

View attachment 351731QUOTE]
Note the use of uuF instead of pF in the schematic.
Of course the tuning dial would be labeled in MegaCycles too.

 

Thanks Crutschow and everyone, but still same problem, I need to use a Varicap. If someone better than me could draw changes been taken in order to adapt this 60's diagram to varicap diode as thank circuit, it will solve my needs. I was checking this 60's schematic a few days back and is not so clear how to get neither the value nor exactly way to diy both RFC1 and RFC2, I guess 15µH. Besides, as I told you, I didn't find so far any add information for what I want. Sorry for the inconvenience and thanks one more time.

 

It's not obvious but it actually should receive and demodulate the FM signal.
You tune it slight off center of the station's frequency so it is on the slope of the receiver's resonant frequency.
This gives a variation in the audio output as the station's frequency is modulated by its audio.

Here (schematic below) is a similar FM 1-tube receiver I built way back in the 60's (actually still have it) ,which was tuned by a dual 15pF variable mechanical capacitor (and notice the selenium rectifier).
Not great sensitivity, but I could pull in local stations with just a simple T dipole antenna made from some 300Ω twin-lead.
(Of course, no stereo).

View attachment 351731

That "regenerative receiver is also a transmitter!! Just supply an adequate audio signal to the "audio out" line and listen to it on another FM receiver of a conventional design.
THAT is the basic flaw of every "regen" rec. that does not include an amplifier stage.

 

I built 3 years ago an audio AM emitter, with a PL500 tube with a range of 200 feet, with adjustable capacitor, and still works pretty good. But for this new diy, I will try to add a varicap diode and modify the tank part of this nice 60's main circuit, because we all know it works for sure, I will remove the Variable Capacitor from the original diagram too, because as I told you I don't like it. Anyway, I will let you know my experience in this matter asap. Thank you all.

 

IF the TS is wanting to create that circuit shown in post #1 with a vari-cap diode, "Good Luck" will be needed.

 

And now I see that removing the cap s because the TS "does not like it".

 

Hi, I don't know if I am posting this in its place. I am designing a FM 1 Tube Rege. 88-108 Mhzs. receiver, tuning by varactor. I have finished my diagram, but I have some doubts anyway. There is a clear lack of this type (varactor) operate receiver in the Web. I am wondering if my design is going to work or close to. Here include my schematic. Any comment!. Thanks a lot.

The problem with using a 1N400X as a varactor is that specs are loose, and you have no assurance of what the characteristics will be from batch to batch and manufacturer to manufacturer. Instead, choose a zener diode. They are much more constrained in how they are constructed. For instance the PN junction is very uniform to ensure the breakdown knee is as abrupt and flat as possible. This results in good varactor operation below the knee. Characteristics will be much more consistent between different sources.

 

There is also the rather huge issue of the lack of the "ground" connection to the two capacitor center-tap of the tuned circuit. That changes the whole circuit quite a bit.

 

i would not worry much about diode. you can change it later too or compensate by stretching or compressing coil. the bigger issue is anode voltage of just 12V. i don't think you can get any of those tubes to run below 60V or so. and that is without heating cathode by passing current through filament? where did inspiration for this circuit come from?

 

Re-visiting that circuit in the post #1 PDF, what the TS has done is removed the feedback portion of the circuit and changed it to a poor amplifier, with cathode degeneration. There was no "design"involved at all, just some redrawing.
Compare the circuit to the circuit shown in post #6, which does include feedback, and understand that there is a great deal of difference between drawing and designing.
It should have hit many of us sooner that a basic element of a regenerative detector is positive feedback. The only feedback in the post #1 circuit is negative feedback by means of the reactance in the cathode circuit.

 

I made a lot of mistakes because I never upload any diagram, sorry.

 

It is also often simple and easy to copy the diagram onto a piece of paper . NOT to trace off the screen but simply to copy the drawing. This circuit is certainly rather simple.