"Jay in the Mojave" wrote in message
...
DR. Death wrote:

I received the board today along with the Motorola engineering bulletin
and
a list of construction hints and ran across my first problem. The
bulletin
lists R4 as 33 ohms. The construction hints lists it as 82 ohms. The web
site resistor package lists it as 47 ohms. Hopefully they can clear this
up
for me. I'll post the results when I get a reply.


Hello DR. Death:

One other thing that could be done to get a feel for the Value of R4 is
look at the other Motorola Engineering Bulletins, and see what they use
for the resistor. 33 and 47 ohms looks like a good value.

One problem I see is that because this resistor needs to dissipate 5 to 6
watts, a lot of these resistors used are too small in there power rating.
Thetas why the 8 watt series/parallel circuit works so well. And the 2
watt carbon Resistors can't be too expensive. See:

http://www.rfparts.com

You could have a 33 ohm and a 47 ohm resistors, and switch between them to
see what what works best.

And of course you could always measure the current of the two transistors
at .6 to .7 Volts applied at the Base and Emitter of the Q3 and Q4
Transistors. This with ohms law would tell the range of resistors used for
the bias supply for a pair MRF242 Transistors.

Jay in the Mojave

If you are really concerned you will want to use 5% or better resistors,
which, can be hard to find in large wattage for cheap. If you want to burn
a little money look into the dale power resistors which have an aluminum
outer heatsink covering. Since this covering is sinked to ground it will
also help with stray RF and may prevent some internal oscillations thus
keeping harmonics down a tad.

http://www.vishay.com/resistors-disc...wer-more-five/

Chad