On a sunny day (20 Sep 2006 02:53:13 -0700) it happened "Telstar Electronics"
wrote in
om:


Frank Gilliland wrote:
No PCB = no cracked traces, copper seperation, no burnt boards, better
heat dissipation, more efficient conductors, etc, etc. Let's face it:
replace the power transistors more than twice on a PCB and your board
(and therfore your amp) is garbage. Not only that, but it also allows
the flexibility to use transistors of different physical sizes and
styles; i.e, the amp can be upgraded or retrofit as desired.

You're losin' it... no PCB at RF frequencies means wires and
uncontrolled inductances / resonances all over the place causing
instabilities... resulting in oscillations. Why don't you think any
commercial amps are built your way.
Great idea Frank... LOL... you're truly a great engineer!

www.telstar-electronics.com

Well, not exactly, I had in the long ago past a nice 40MHz army transceiver,
toobes!!! (called '32set' IIRC) 40 MHz FM full of toobes and no PCB anywhere.
My own 500W linear PEP with toobe had no PCB either.
If you go to a real shortwave station, 10kW and up, they use big plumbing,
big toobes sometimes... (these days transistors too in modules OK).
PCB (an as already mentioned by somebody): the thickness of PCB traces becomes
a BIG issue especially if you run 1kW at 12V, a few milli-ohm will give
you big i^2 x R losses.
So copper strip is better anyways, lower current, and higher voltages, FETS,
means lower losses, you will need the switch-mode to get the higher voltage.
Switch-mode design 50V many amps is an art in itself, I have done switchmode
design for a company, it will take you study and time, and likely a few
transistor failures.

Soldering copper strips to these transistors will require you to support these
with proper spacers, so as not to mechanically load the transistors too much.
Else vibrations will rip the connections right of over time.

I like Franks idea, it is a lot like this one:
http://www.ibelings.com/n4ip/mrf157.html
I looked up the price of those FETS, 475$ each :-)
But I also found a pair on offer for less then 60$, was already gone however.
http://www.sphere.bc.ca/test/rf-semis.html
other interesting stuff there too:-)
In my school days I used to sell Motorola parts...... to finance my hobby.


So, anyways, long before the kids had PeeSeeBees the big boys were using
copper [wiring], and it did not [always] oscillate.
And in the old toobe times the voltages were more 'electrifying' too, mine
ran on 1kV, some used much higher voltage power supplies, dangerous these big
capacitors.
So the Telstar amp is just a small toy..... compared to what was done already
in and just after WW2.

But do not let that put you off, it looks like a nice amp.
And Frank will still have to build his ;-)


BTW you Americans have 110V, I had some BUZ44A (IIRC) MOSFETS that can do
500V DC, these oscillated (unwanted) around 20MHz, one could just plug it in
for a base station.... No voltage converter needed, not even a transformer.
Not sure if something like BUZ44A can be used as an amp.... at 27MHz.
http://www.datasheetarchive.com/data...rticle=1048164
probably to much input capacitance 1600 pF.....

But looking around for a nice FET may be worth it.