Swapping IRFP9240/240's for SC5200/SA1943's??

[richie00boy]

Sorry, my bad. I meant to say:

Surely the power dissipated in MOSFETs not under saturation is exactly the same as with BJTs?

I agree with you totally on the clipping scenario, but you also said:

The IRF's will actually dissipate a lot more heat at any given power output

Which is not correct IMO, and was what I was getting at.

 

[Stuart Easson]

you are quite right...

...that'll teach me not to generalize. As is clearly the case, the device dissipated power at levels below the clip point should be the same.

As long as I do the maths before I post I do OK. OTOH shooting from the hip generally hits my foot, which I then obviously put in my mouth...

Stuart

 

[jacco vermeulen]

Re: not quite...

Changing the amp to allow for higher voltage drive is not hard, but adds considerable complexity to the swapping rework...there's a very good reason why every well designed mosfet amp uses a higher rail for the VAS etc, it actually reduces the size of the power supply needed to achieve a given output power...

I think those lines are THE most important reason not to swap Mosfets for BJT's.

Though for any front end and output stage applicable i should think it is quite a waste of energy and heat to run Mosfet amps on a single voltage level supply.
Especially given the relatively low required current for the stages up to the driver, a small step-up transformer often will do.
The MJE or MJ15*** series have become quite affordable, often a few extra can be added easilly and nothing needs to altered.

 

[Zero Cool]

Re: not quite...

I still maintain a quad of mje21193/4 will be the best answer...

Stuart

I will see what i can do to aquire some of these and swap them in.

Thanks

Zc

 

[Zero Cool]

Whats the difference between MJE21193/4 devices and MJL21193/4 devices???

I cannot fine the MJE units but can get the MJL's for about $5.00 each


ZC

 

[Stuart Easson]

package

Sorry I mistyped, the mjl's are the plastic packaged, the mj21193/4 are TO3 versions, which have somewhat better power rating, but most everything else is the same I think.

If you decide to go with them, you can get the MJL's for $3.50ish from http://www.tech-diy.com , the owner's a forum member and typically has great prices and service. Plan B might be to register with On-Semi and get samples...sounds like you might be fixing a few of these...

Stuart

 

[Zero Cool]

Ok well i ordered some samples from On Semi. I am still trying to figure out there number system. for example. the have a MPSA92 device and a MPSW92 device that looks exactly the same to me. whats the difference between the A and the W devices???

I ordered samples of the MJL21193/4 and the MJW21193/4's as well.

hopefully i wont let the magik smoke out of these! Boy if i could only find a way to get that smoke back in there I would be RICH!

And i see they have some new devices that arent available as samples yet that match the specs of the C5200's exactly! so On Semi must be making some replacement devices.

I also ordered some MJL3281 and MJL1302's which appear to be On Semis version of the toshiba parts.

Zc