I am trying to use a VHF transistor whose collector is internally connected to the case to provide a ~2W output. Now, running at that sort of power, it's clear that you need a heat sink on the case yet, so far as I can see, any decent heat sink would add enormously to the collector-to-ground capacitance and, working up in the 100MHz+ range (still less for the 400MHz the transistor is rated at), that looks pretty prohibitive.

Here is the setup recommended by the manufacturer:




and here are the specs they give.

Ideally I'd want the case to be isolated as in the now-discontinued 2N3375 and so use a nice case-ground.

What would be the usual workaround here?

 

Hello,

You could use a heasink in the style given on this page of digikey:
http://www.digikey.com/product-sear...t=0&page=1&quantity=0&ptm=0&fid=0&pageSize=25

Bertus

 

Another common solution is to use the collector to heat sink capacitance as part of the matching network.

 

newer types of transistors have the case tied to the emitter, allowing the case to be grounded. they typicly have higher output than the older types.

 

Thanks for the suggestions/observations. Would I be right in saying that for VHF transistors operating much over 1W the general move has been to use FETs? Apart from the high input capacitance and possibly the cost, is there any other disadvantage to using a FET?