Hi, I am trying to make a simple fm tuner as per the circuit diagram attached. Problem is, BF494 transistors are not readily available in my locality. Hence, I have used 2N3904 transistors as an alternative choice but the tuner doesn't seems to work. Can this transistor be used in this circuit?

 

That would be a pretty poor detector.

A 2N3904 is an excellent choice for this circuit, indeed I have used a 2N3904 in a circuit like the one below.

This (below) would be much better. It is a regenerative detector.

http://www.vk2zay.net/article/195

 

The original circuit is a latch with DC positive feedback, not a radio.
If the latch transistors operated like a regen amplifier then the circuit would detect AM pops and clicks interference but will receive an FM station if it is tuned to the side of a station and detect the FM by "slope demodulation".

It would probably pickup a few FM stations at the same time because it has only one tuned LC circuit.
It would sound very muffled like an AM radio because it is missing the pre-emphasis that all FM radios have.

Correctionl It is the FM radio station transmitter that has pre-emphasis (treble boost). Then all FM radios have ds-emphasis Treble reduction. Nit this simple radio does not has a de-emphasis filter so it will sound shrill and harsh.

 

That would be a pretty poor detector.

A 2N3904 is an excellent choice for this circuit, indeed I have used a 2N3904 in a circuit like the one below.

This (below) would be much better. It is a regenerative detector.
View attachment 306556
http://www.vk2zay.net/article/195

Hi Dick, thank you so much for sharing this circuit with me. I will definitely follow your suggestion and build this one. I have one doubt that I'd like to clarify, could you please tell me the turns and uH rating of the 1st inductor?

 

The circuit looks a lot like the one-tube regenerative receiver publishes about 1962. It will be able to receive FM but it will also transmit and this will not be good. Not a good receiver but not everybody can tell the difference.