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25w fm amplifier

25W FM Radio Amplifier Circuit

A simple 25W fm radio amplifier used as a final stage for a 2.5W transmitter. I has a total gain of 10 dB and needs a 12V / 3A power supply. It is equiped with KT925W or BLY88, BLY89C. Use a very good headsink because this transistor get very hot 🙂

Coils values:
L1 = L3 = 4 turns / 1.5mm / 8mm / 10mm long
L2 = 4 turns / 1mm/6mm/10mm long
L4 = 20 turns / 0.8mm / on 22Ω resistor

25W FM radio amplifier circuit schematic

25w fm amplifier

32 Comments

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  • tong

    If i don’t have SWR-Watt meter, am i have hard to do it?

  • tapash parui

    sir please send my emil 25w amplifier’s 22 ohms . 10 ohms and 100ohms resistor watt valu and l4 coil dia meter and 3uh coil valu.

  • Dovydas

    Can i use KT925B transistor instead KT925W?

  • EngMsr

    one more question
    how to connect that 1nf cap at the supply
    thnx

    • P. Marian

      Between plus and minus, it is a special thru-hole capacitor, but you can use an ordinary one too.

    • EngMsr

      wont it block the dc current and prevent biasing of the transistor ?

  • EngMsr

    hey there
    is that 3uH coil is an SMD ? pls advise thnx

    • P. Marian

      no, it is not a SMD coil. It is made on a ferrite core.

    • raj

      Another question:-
      -Are there two 56pf capacitor connecting base to ground? Or one 56pf is Positive supply to base?
      – and what will happen if I feed this amp with 4 watt rf?

    • raj

      -3uH mean…resistor type small inductor? May I use 4.7uH (color band:- Yello Violet Golden) OR, 2.7uH ( Red Violet Golden )?
      -Is it not necessary to give fix diameter and fix length to L4? Just to wind over 22 ohm resistor of any shape?

  • platch

    Hello Guys,

    I just would like to know the power/wattage of this resistor 22. 1w is enough? Please advise.

    • P. Marian

      You can use a 0.25W too because the DC current is going thru the L4 coil. The resistor will get hot if there is high RF current when the antenna is not corectly tuned.

  • iran miss

    schematic boarb smd of 25 watt rf with bly89 or 50watt by bly94 plz.

  • Finland

    Whit 2W drive i get 18W out, when driving 2.5W i get about 28W out after hard tuning.
    When its ready and i turn it on, its give only poor 13Watts.
    It’s take 2hours to tune it but after that, it’s runs very well.

    Last night, i broadcasted 6hours 😀

    • P. Marian

      I am glad to hear that, are you from Finland?

    • Finland

      Yes i’m, This little linear runs very well.
      I added better lowpass filter, whit out it it’s make lot’s of harmonics
      Only what i need to do is change heatsink to bigger one and add fan on it.

    • nielplatch

      Hi Finland, can you please email me how you made yours? am very eager to have it try. but am not professional with this stuff that’s what i badly needed the details. Hope to hear you soon.

    • P. Marian

      Can you send me some photos with the amplifier? I want to post them on this article. Thanks.

    • Finland

      Search gray aluminium box, add power switch and fan, now take a photo 😀

      I don’t have digitalcamera so maybe it take some time to get it somewhere.
      Or I need ask someone to take photos and send them to You.

  • ziddik

    does it transmit fm signals upto 50 kilometeres of distance?

    • Finland

      Whit dipole on 15m above ground i get about 20km, whit poor 70cm whip only 700m.

      Antenna is best amplifier!

  • Andrew Ssewava

    i believe everything is possible as long as there is a combined ideas in electronics most especially in our field of communication guys we need to share the ideas and i thank all trying to share with the young generations thanks a lot.

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