Mosfet experimentation OR how far is too far

[Turbine Divinity]

Okay since I have had allot of fun modding the snot out of Old Cobra 29's with the IRF520. the questions now become "how far has anyone gotten with a Mosfet Mod?"

Has anyone taken it the next step? 40 - 50 watts seems to be the best you can expect from the current crop of Mosfets. But have we seen higher?

I have been looking at some other Mosfets with much higher gain and have been considering a few experiments. But without treading into work that has already been done . I am curious what people have achieved (if anything)

I know heat quickly becomes an issue along with a myriad of others. But can we see an 80 watt mosfet hack here without rebuilding half the transmit section?

Just curious

 

[Robb]

There is an ERF-7530 device that can sustain 75 watts PEP with a ERF-2030 driver. The 7530 is actually capable of more - of course - but can run 75w reasonable duty cycle. Used first in the RFX-75 add-in amps. Spec sheet is here:
http://www.cbtricks.com/miscellaneo.../rfx_75/graphics/erf7530_datasheet_rev2_0.pdf
http://www.cbtricks.com/miscellaneous/accessories/power_band/rfx_75/index.htm

Then, there are RF amps made of several IRF-520's built by RangerUSA - placed in the RCI-2970N2 - producing 200w PEP.
Very popular radio - BTW.
http://www.bellscb.com/products/tenmeter/ranger/RCI_2970_N2.htm

Magnum Int'l makes the 'Power Cabinet' unit - using ERF-7530's instead of IRF-520's to accomplish the same thing.
http://www.cbtricks.com/miscellaneous/accessories/magnum/sx_175/index.htm

And yes - they all fail when pushed past the 2/3 of full power limit - regardless of who makes the amps.

Not sure if the circuit must be altered to change from ERF-2030's to IRF-520's. They are supposed to be interchangeable - I've never done it.

 

[Turbine Divinity]

How about this

I was considering figgurig out how to drive this bugger with the addition of a better heatsink.

http://www.vishay.com/docs/91019/91019.pdf

A bunch of issues begin to show themselves but are they insurmountable to keep it "in the box"

Now where are my screwdrivers.

 

[W5LZ]

The 'mainest' problem with any mosfet is that they are not very linear as compared to a 'regular' transistor. That linearity has a narrower range, which means that if you don't keep that mosfet in that range, you will not care for the results. That typically means that at some point, rebuilding the whole transmitter section is going to be the only way to get more out of a mosfet. The best way around that is by starting fresh, don't 'rebuild' anything. That's certainly not the easiest way, but sure seems like the best, doesn't it?
That certainly doesn't mean that mosfets aren't useful, and maybe (big maybe) the device of the 'future', but they certainly do have limits.
- 'Doc