Bill, W6WRT wrote:
> ORIGINAL MESSAGE:
>
> On Fri, 26 Mar 2010 10:17:53 -0400, "Carl" <km1h@jeremy.mv.com> wrote:
>
>
>> For the technically savy and safety knowledgeable why not go AC/DC?
>>
>
> REPLY:
>
> I have been waiting for years for reasonably priced transistors which
> can deliver 1500 watts while running of a line-rectified 150 VDC.
The problem with transistors is two fold. One is getting rid of the
heat. The transistors are small meaning a small area for heat conduction
and a high delta T even with the best of heat sink compounds. So, even
with adequately rated transistors it often takes several of them to get
sufficient heat transfer to keep the operating temp down to a reasonable
value.
The second problem is the elaborate protection circuitry. Transistors
must be protected from voltage, current, over drive, and temperature.
The over voltage protection circuitry can come from the SWR circuit.
Unlike tubes which can *usually* tolerate over current and over drive
for a short time (depending on the tube) with no detrimental
effects/results, transistors can be destroyed by a single pulse of over
voltage or over drive and they are not good at handling over current.
What we need to do in these cases is treat each parameter with a
separate approach which greatly simplifies things, but still those
protection circuits need to be fast! The circuits in the Tokyo Hy-Power
amps are impressive. I've not had a chance to play with the Icom and
Yaesu solid state amps.
IIRC there was some one on here about a year ago developing a legal
limit, rugged, SS amp. I remember a number of e-mails where I talked
with them about cooling and the support they were receiving from some of
the manufacturers with the protective approach.
So there is some work going on with big solid state amps. I don't know
how that particular project turned out.
> I
> think they're getting close, but they are still pretty expensive.
>
And fragile.
73
Roger (K8RI)
> 73, Bill W6WRT
> _______________________________________________
> Amps mailing list
> Amps@contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
>
>
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|