Yes, I worked with audio equipment in my career but I am retired now.
My FM transmitter works fine from a 9V battery until it runs down to 6V. It might get too hot with 12V.
Someone designed a pcb for it but I haven't tried it:

 

A 9V battery is "dead" when its loaded voltage drops as low as 6V but the 5V low dropout voltage regulator I used (that one is now obsolete but there are many newer ones) still regulates perfectly with a 6V input.

The circuit that I designed and built is in post #18 in this thread. I did not test the "tweaked" values, instead I simulated different values until the simulation had the most output and the least distortion. It might be different when built.
I also did not try the two pcb layouts, the other layout has ".brd" and ".sch" file types that I have never opened and cannot post on this site.

I am sorry that I do not have time to compare parts on the pcb layout with the actual parts on my schematics.

 

The text of the Micro pll FM Transmitter has a poor translation into "Engrish".
1) The audio is missing pre-emphasis that all FM radio stations including my FM transmitter have to match the de-emphasis that all FM radios have. Then the audio will sound very muffled because all medium and high audio frequencies will be reduced like your stereo with its treble tone control turned all the way down.
2) The preamp opamp is inverting with a very low input resistance (R4= 100 ohms) which reduces the output signal from the mic to about 1/27th) and the low value for C4 cuts low audio frequencies.
3) The TL061 preamp opamp is not an audio low noise type, it does not work when the battery drops below 7V and its gain is extremely high (R1 is 10M) which results in a very high noise level.
4) I do not see an RF oscillator and since it is supposed to work at the 4th harmonic then the output signal will be weak.

 

Sorry I didn't answer your questions.
1) My FM transmitter works well and sounds great. I doubt the pll transmitter works but if it does then its radio signal will be weak and it will sound awful.
2) Post #18 shows my transmitter's schematic and the compact stripboard layout I used. The pcb I posted was made for my FM transmitter but I did not check it.
3) The LM2931Z-5.0 low dropout 5V regulator is still made and available at Digikey.

 

The Z is the TO-92 little TO-92 transistor package from manufacturers that make the LM2931 in many other packages. The LM2931 without the Z is made by manufacturers that make it only in the TO-92 package. The A is with a slightly tighter tolerance of its output voltage from 4.81V to 5.19V and without the A the output voltage is from 4.75V to 5.25V. Pick the least expensive one. Ones from ebay, Amazon or Aliexpress might be defective or fake.

I posted a pcb layout made by somebody else of my circuit in post #23 here but I didn't use it and didn't check it.

 

Sometimes I can hear the music on my cell phone at a frequency of 100.35 MHz but mostly its all noisy...

prsarr plz tell me u have 3-meter receiver app on your cell cuz otherwise it's case of _slope detection_ in phone's audio circuits or wicked harmonics with phone reverting to analog mode

 

obtw @Audioguru and @Dodgydave huge tnx for showing ppl proper xmitter design (instead of like _VXOed_ digital oscillator that keeps popping up on project threads)!

 

I show the pcb layout with my original schematic. I marked the parts values and a brief description of each one. Some are wrongly marked pf instead of pF. You can use "tweaked" parts values if you want.
The resistors should be 1/4W, 5%, carbon film.
The pcb layout has the spacing for the coils too large and the spacing for film capacitors also too large. Whatever trimmer capacitor size you find probably will have 3 legs (the ones on the pcb have only 2 legs) and different spacing.

 

I show the pcb layout with my original schematic. I marked the parts values and a brief description of each one. Some are wrongly marked pf instead of pF. You can use "tweaked" parts values if you want.
The resistors should be 1/4W, 5%, carbon film.
The pcb layout has the spacing for the coils too large and the spacing for film capacitors also too large. Whatever trimmer capacitor size you find probably will have 3 legs (the ones on the pcb have only 2 legs) and different spacing.

Ingenious efforts put in, Glad. Very soon il put one alive .

 

I made a 2 transistor fm transmitter but it seens like it doesn't work. The schematic and real image is attached, i used 2n222a transistors in place of 2n3904.View attachment 144549

View attachment 144550

you really need to put this kind of circuit in a metal box, make sure there's no unwanted contact to the box, shut the box with enough screws, make sure the through holes again do not touch the box, then you can test this circuit.