[AMPS] FET Power Amps

[David B. Ritchie]

Icom makes a very nice amp, albeit incredibly expensive and not quite 1500W
Japan Radio makes a nice MOSFET amp at the 1000W level -- also very 
expensive.
The big problem with solid state is that you trade volts for amps and 
volts are, at least for now, easier to deal with and cheaper than amps.  
You should see the power supply for the 18Kw LARCAN they use at KCBS-TV 
in Los Angeles -- if you dropped a monkey wrench across its terminals, 
you'd wind up breathing the monkey wrench.  The power supply is huge -- 
much larger than the HV power supply it replaced.  BUT, the MOSFETS 
appear to be more reliable -- they fail, but only one or two at a time, 
and because the entire installation is modularized into 1kw plug-in 
modules, the techs just solder in new transistors when they feel like it 
without bringing the transmitter down.  Its very nice, but its not 
cheap.  Tubes are cheap.  What is the most you could possibly pay for a 
1500 W tube?  $1200 - max -- less if you are willing to use surplus, used 
or pulls (which we are all willing to do or this news group wouldn't 
exist).  You are not going to find $200 50W Mosfets available cheap, used 
and surplus (which aren't fried like the one sitting in front of me right 
now) for some time to come.  And its harder to build -- a lot of stuff 
all running in parallel on stripline or circuit boards rather than a nice 
socket and some HV wire and a couple of vacuum caps.

Oh -- Ameritron has a couple of 500+W class amps for DC -- you have to 
supply your own power supply -- probably best to just use a car battery 
and a charger.

So to conclude -- current technology doesn't permit cheap desktop 1.5KW 
amps -- you can do it, but the desktop has to be pretty sturdy and you 
pockets will need to be deep.

Dave N7UE



On Fri, 28 Mar 1997, Lee Buller wrote:

> I was listen to some guys on 75 meters the other night (Nothing was good on
> TV) and they were talking about FET amplifiers.  They seemed to be quite
> informed about the subject.  
> 
> My questions is this...where is the technology today to have a big old harry
> 1.5 KW amp with enough headroom that uses solid state devices?
> 
> I know that is broadcasting (AM and FM) a lot of rigs are being produced use
> solid state devices.  I know Harris, BE, Continental, Elcom/Baur and a
> others are doing this...on FM and AM.  Why hasn't the designs made it to ham
> radio?
> 
> Thanks for the comments....or flames.
> 
> Lee
> k0wa@southwind.net
> 
> 
> --
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David B. Ritchie, Esq.
D'Alessandro & Ritchie, P.C. -- Intellectual Property Lawyers
3521 E. Yorkshire Road, Pasadena, CA  91107-5432
818-683-8800 (TEL)   818-683-8900 (FAX)   dbr@alumni.caltech.edu


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