Amp help

[XXL]

Looking for some help on this amp. Not too sure what iv done wrong here. Probably not the best way of using these 2 devices but hopefully it will still work semi ok for now.

The coil to the RD15 drain starts to fry when applying voltage. The bias is not turned on/up at all.

Also it’s just a prototype iv built on a board that was meant for something else, don’t worry about the tracks.

https://pasteboard.co/IFpQw96.jpg

[sinus trouble]

How much current is drawn as you turn up the supply voltage? That is with no RF drive applied or bias!

[XXL]

No RF drive or bias. Still fry’s the coil. Iv beeped it all out, no shorts.

I’m baffled.

[sinus trouble]

Well that is a start! You still need to monitor the current when powering up!
Your bias pot also seems to be backwards? or is it just the pic?
the coil could possibly be too thin? but I doubt it, especially in an idle state!

[nrgkits.nz]

Start by removing the RD from the board and then checking the resistance between the drain and source, you may find the device has been fried and there’s low resistance between the two pins.

[sinus trouble]

Totally agree G!
There should be no load on that coil unless you have a dodgey FET or bias problems!

With zero gate bias and no RF drive the current consumption should be a few milliamps mainly to the regulator.

[sinus trouble]

The orientation of your bias pot would lead to a regulator short and unstable bias voltages if my eyes are correct?

Remember FETs can be gate charged with very little voltage and current due to their high impedance!

[XXL]

It’s like there’s a dead short. When I put the multimeter on the drain it beeps slightly, then stops. I left it plugged in and let it fry the coil. The fet popped. I replaced it, and doing the same thing. I’ll change the pot and lift the fet up. Thanks

[sinus trouble]

When you use a multimeter on diode test (beep) you are actually charging the gate with voltage which can cause the FET to conduct! The temporary short you are getting is quite normal, if it persists? there is a problem!

As I suggested previously a PSU that can display and limit current is essential for electronics! Trust me it will save you a lot of money in the long term!

[XXL]

I think it needs tuning between the fet and the sd1407, but I can’t turn it on for long enough to try different values. I’m guessing I couldn’t leave it on if I had a current limiter.

[sinus trouble]

It is highly unlikely to be your matching circuit at fault if you have zero bias or drive! And its decoupled from the DC also!

You will need to check the gate has no unusual voltages present and drain current