"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

"Chad Wahls" wrote in message
...

"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


That's an excellent suggestion A little more money sure won't break the
budget on this project. Thanks.

"DR. Death" wrote in message
...
"Chad Wahls" wrote in message
...

"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


That's an excellent suggestion A little more money sure won't break the
budget on this project. Thanks.



Frank said it would be a moot point to have RF rejection in this area, do
trust him more than me as he has WAY more RF knowledge than I do. I'm an
audio guy!

BTW what's the budget on the project? Just curious.

Chad

On Fri, 22 Oct 2004 08:17:01 -0500, "Chad Wahls"
wrote in :

snip
Frank said it would be a moot point to have RF rejection in this area, do
trust him more than me as he has WAY more RF knowledge than I do......


Sorry, I wasn't trying to step on your toes. You probably didn't know
that the input impedance of these transistors is about 1 ohm (with a
little reactance), and I think you will agree that any pickup by this
resistor (or other relatively short wiring in the low-impedance part
of the circuit) isn't going to amount to squat. Regardless, any RF
that happens to land on the center-tap of the input transformer will
end up as common-mode signals that will be nulled at the output
transformer.

The most likely cause of self-oscillitory feedback will probably come
from the relay. Notice that one relay is used for both the input and
output (both at higher impedance than the amp block), and that the
armatures are long, parallel, and relatively close together. Scary!
Even Pride, the company that produced some of the worst CB amps ever,
had enough sense to use two seperate relays.







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"Chad Wahls" wrote in message
...

"DR. Death" wrote in message
...
"Chad Wahls" wrote in message
...

"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


That's an excellent suggestion A little more money sure won't break
the
budget on this project. Thanks.



Frank said it would be a moot point to have RF rejection in this area, do
trust him more than me as he has WAY more RF knowledge than I do. I'm an
audio guy!

BTW what's the budget on the project? Just curious.

Chad


I'm pretty sure I should be able to do this for $75 or less. I've had the
454s in a drawer for about 15 years. I have most of the switches, caps,
resistors, diodes and transistors. The heatsink was a freebie. I'll build my
own enclosure. SO239s robbed from old radios. Really the only things left to
buy is the relay, the resistor in question, and the transistor. So far I
only have $33 in it.