Anyone help with this ?

[Classic]

Ok thanks I will look over it, but at a glance the gate voltage should never exceed 20V as it clamped with a zenner.

So from the diagram is there anything i can change to get the gate voltage to 4 volts as black spirit recommended ?

The MOSFET Gate is tolerant to +/-20V, the gate is clamped to a maximum of 20V with the zenner diode - I am not sure why it is failing - I would try a different device - is it genuine or a Chinese import?

Not sure it's a irf520n international rectifier. I thing they are real but can't be 100%.

[Classic]

Also check the gate voltage with a DVM and an FM carrier not exceeding 5W, check the diodes and the zenner diode to be sure.

All the diodes have been changed and it's still the same.
It's obvious they are fake or someone gave me the wrong advice by saying i could use one in that amp.

[2E1IIP]

I would not chuck in the towel just yet, there are a few clever blokes on here who might have other suggestions.
If you go to a supplier like Radio Spares, Farnell or Mouser you are very unlikely to get fake/inferior parts - here is an example:
http://uk.rs-online.com/web/p/mosfet-tr ... s/5411180/
I am not saying that it is 100% a fake part although I would certainly eliminate that from the list of possibilities.

[Classic]

I would not chuck in the towel just yet, there are a few clever blokes on here who might have other suggestions.
If you go to a supplier like Radio Spares, Farnell or Mouser you are very unlikely to get fake/inferior parts - here is an example:
http://uk.rs-online.com/web/p/mosfet-tr ... s/5411180/
I am not saying that it is 100% a fake part although I would certainly eliminate that from the list of possibilities.

I have lots of irf520n's i think they are real as i've been doing some research on the fakes and it looks like they are real. Just wish i could use them in this amp.

[dt307]

http://uk.farnell.com/fairchild-semicon ... dp/2453903

all i use for ss3900/rm amps /ss9900/at6666 ect

gave voltage from 3.6-4.3 (norm3.7)

pm me your addy and i send you two for free m8 to try

[Classic]

http://uk.farnell.com/fairchild-semicon ... dp/2453903

all i use for ss3900/rm amps /ss9900/at6666 ect

gave voltage from 3.6-4.3 (norm3.7)

pm me your addy and i send you two for free m8 to try

Thanls alot mate.

[Classic]

How much power are you putting into the amp ?, It must be kept below 4w, Also the Mosfet will burn up quickly if the gate voltage is too high [over 4v].

Ive lowered the input power and the gate volt is around 8 volts on about 1 watt in. Is that meant to happen ?

[163TM847]

I would say 8v TX gate voltage is way to high, It should be no more than 4v at all times, Personally i dont think its worth messing with as you can get small 15/20w amps cheap enough, I have a few amps [MRF455 transistor, Some may describe it as a 100w amp but realistically 5w in FM and i am getting 60w out which is about right] I would probably sell it off cheap.

[dt307]

as the man said 8v way too much 4.3 is max depending on application 3.8 is a good starting point and give a little more if needed

[Classic]

as the man said 8v way too much 4.3 is max depending on application 3.8 is a good starting point and give a little more if needed

So how do i get the voltage to stay in that range ? I've tried another transistor and it's still doing the same,starts at 12 watts goes down to 8 watts.