this is my second try in fm amplifier using a mosfet rd15hfv1.i only get 3 watts anyone with good design please .i need it quickly.i tried to build the FRB one free radio berkley get the paper from a friend what is wrong ? sorry image not high quality my camera phone is bad .but can be seen as buildirs and professionel like you what is the maximum supply on the BIAS if i increase the bias the power increase too .bias is biased from 5volt reg 7805.

I have not used one of those devices yet but how did you set the bias up on the amplifier? From looking at the datasheet it appears to need a quiescent current of 0.5A @175mhz, so would assume it needs the same at 100Mhz.

Have you connected an amp meter in series with the supply to the amplifier to see if it is drawing that? (with no input rf connnected).

Hello again Mr Radium
If you have built it to the correct specification? I dont see why it wouldnt work? The bias is set up by disconnecting the positive supply lead and connecting a current meter in line! you then adjust the bias potentiometer to the required Drain quiescent current (Idq) in mA! it is important that you carry this out with no drive connected!
A few Points?
By the picture? i assume you are driving it with 1watt?
What Power supply are you using?? (regulated 2 amp capable at least) Your DC leads are FAR TOO THIN!!
Where is your heatsink??

Yess Mr 2000!
Im not sure he will get any current at all from the DC supply leads! They look like bell wire or something lol!?

thank you for reply and pointing to help me

hi friend sinus trouble.sorry for bad quality pictures.lol dc power cable yess are thin and heatsink is now disconnected right i have a good ps capable of 6 amps i generate exitation from pira 1w pll good power through pi network to compensate drive while it only needs 200 mw but i am not sure cable are thin but not warm at all tomorrow i will replace them but this is not the problem i only could get 3 watts with bias up to 3.25volts

@ s2000 i will look through also iand inform here.

Sounds like your drive and and PSU are great!
I cannot stress enough how important your supply leads are! just because they are not warm, it does not mean they are ok! wires that thin can cause a huge voltage drop! you need to change them asap! keep them short and Thick!
Bias voltage is irrelevant! You need to know when the specific device comes into conduction! the only way you can do that is by measuing the drain current via an amp meter!

Haha do love a bit of bell wire

Have a look at this thread Radium... it has a interesting video on it that shows you how to set up amps etc... What you are looking for is not voltage but current draw...

viewtopic.php?f=11&t=1149&p=11821&hilit=bias#p11821

LOL!!! I think bell wire should be banned!! Ive seen people wire up mains sockets with that shite!!
Good Vid though! Its a shame that the majority of multimeter owners have never used as an Ammeter! Its a great tool and easy if you understand it!

It's probably a fake RD15 transistor.

I agree,probably fake transistor. One of my China transmitters(have two and one is suprisingly good)using the same mosfet as in your amp. I have never had less output than 15Bird with it. Some weeks ago a managed to blow the output due a bad antenna connection and bougt two new transistors. I'd didn't think it ever should get that output again but now with the new transistor it reached the magical 20Bird limit!

I suspect there is lot of fake transistors out there,i like the RD15, it makes it possible to build good small RF amps at the same level as those BGY33 units but cheaper!

wolfmanjack i agree totally i get many fakes but this one is real i just removed from a working PA

maybe you burn the RD15 by taking it out the working board?
A few weeks ago i need some RD15s but RFparts.com was out of stock so i orderd on ebay
They didnt work and blow my inductors in the drain to the power supply
After putting a new RD15 from the same order in my component tester the source was on the right and not in the middle like then original RD15 and gate was about 1090pF and the original about 20-30pf
After going trough my stock and testing a few standard mosfets i found the same specs it was a IRF 510
Lol chinese fakes

@ analyser please check your mail

after a hard work with a 1w BW pll exciter and after strtshing coils i can get 6watts .but why with no rf input transistor heat up and when i put rf from exciter it cool down to normal temperature

Analyser wrote:It's probably a fake RD15 transistor.

I accidentally bought a fake whilst on holiday in Thailand, when the RD series first came out over 10 years ago.
It proper blew my mind when I managed to get 30W out of the thing.


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