[BC] high power transistors for FM

[John Lyles]

Many FM and VHF tv amplifiers were developed using the generic design which started with the Motorola MRF151G part or variants which can take 50 VDC on the drain from Philips, ST, Freescale, M/ACOM (Tyco) etc.. I am wondering when the broadcast designers will start to move to higher voltage devices at 108 MHz such as:

ARF473 from Advanced Power Technology (now Microsemi) capable of 300 watts with 135 volts
IXZ2210N50L from DEI (now part of IXYS) capable of 300 watts CW with 150 Volts,

I wonder whats holding back these developments, low reliability, VSWR trouble, linearity? Maybe someone has got newer generation parts in their box now. Certainly would make the matching a lot easier on the pallets. What became of Silicon Carbide based devices, that could run higher junction temperature. Remember the  developmental transmitter at NAB - was it Westinghouse? 

John

> One of the main advantages of solid state  is that not all the eggs  are in 
> one or two tubes.   Called "Soft Failure"   loss of  one or two modules only 
> reduces power output.  It does not affect the air  sound in other ways.  Simple 
> replace the module and back to normal.   In many systems loss of more than two 
> modules begins to changed the combiner  system which becomes less efficient 
> meaning it makes more heat.
>  
> Still one of the problems is that in FM we are still using a 48 volt device  
> (MOSFET)  with VHF capability of 88-108 mHz of 300 to 400 Watts analog  Class 
> C FM Power.  Depending on your output power it starts with combing  two of 
> these devices and going up.
>  
> Maybe FM will get a 100 or 200 Volt MOSFET allowing more efficient solid  
> state transmitters by making more power per single device using fewer  combiners
>  
> Dave Hultsman
> Continental ELectronics
> 
>