On 21 Sep 2006 17:31:24 -0700, "Telstar Electronics"
wrote in
.com:

True, if you expect the transistors to never be replaced. But that's
not the reality with CB amps. The owners like to swap transistors for
more power. Either that, or they overdrive the transistors and blow
them up. Replacing them tears up the board, which is why it's hard to
find an old single-board amp with good traces. Point-to-point wiring
eliminates this problem because both the transistors -and- the strips
can be replaced. The servicable life of the amp is almost indefinite
irrespective of the amount of work done to it.

Transistors in amps normally have to be replaced because the amp has
matching problems or inadequate cooling... or both. Almost all the
bootleg amps I've worked with suffered from these problems. This causes
the transistors to run red hot... and it cuts their life drastically.


Most of the bootleg amps are usually overdriven. For example, the
Pride 100 is rated for 100 watts output. But most ampheads don't know
that 100 watts means the peak power output, and when running AM they
need to reduce the input power until the output is only 25 watts
(unfortunately, the word "attenuator" isn't part of the amphead
lexicon). Then they key down for far longer than the designed duty
cycle permits ("duty cycle" also not a part of amphead vocabulary).
And -that's- why the transistors are frequently cooked. And -that's-
why this amp is going to have a variable attenuator on the front end,
a thermostatically controlled fan, and will include very detailed
instructions on how to set up the amp for different operating modes.

As far as "matching problems", if you are referring to mismatched gain
in transistor pairs, that only causes harmonics. If the mismatch is
great enough to cause one transistor to run hotter than the other,
that would be due either to component failure or ****-poor quality
control.


As for your statement about using point to point wiring... bad idea.
This causes stray inductances and capacitances all over the place that
cause RF oscillations. Oscillations contribute to failed power
transistors, due to the tremendous power dissipation that is present
during these oscillations. Many times these oscillations can't be heard
on the air and do their damage without the operator ever knowing why
the failure occured.


Not only are you repeating yourself, but you are -way- out in left
field with this concern.....

Power RF bipolars are inherently stable and not likely to oscillate
(assuming no wiring errors) because (a) the input impedance is so low
that stray RF is going to be heavily damped, and (b) the power gain
isn't high enough to overcome the low impedance at the base. You have
to intentionally force these things to oscillate, and even then they
won't start without a solid kick. Ironically, the only bipolar amp I
have seen that -did- oscillate was a single-board design that someone
tried to modify for more power [insert Tim Taylor grunt here].

FET's are different because of the high input impedance at the gate.
But point-to-point wiring has been used both successfully and reliably
in commercial high-power RF transmitters ever since Molly Brown took a
ride in a lifeboat. Oscillation problems were resolved long ago when
tubes were the only choice. Damping isn't difficult, and shielding
between the input and output circuits is a common practice with both
FET's and tubes. All you need is a thin sheet of copper, aluminum, or
even a blank PC board. Got tin snips?

Frank Gilliland wrote:
As far as "matching problems", if you are referring to mismatched gain
in transistor pairs, that only causes harmonics. If the mismatch is
great enough to cause one transistor to run hotter than the other,
that would be due either to component failure or ****-poor quality
control.

No, I'm talking about impedance matching problems. On the input is not
a big issue... only reducing the available drive... but a mismatch on
the output is critical... and causes big problems with excessive
transistor heating... leading to premature failure.

www.telstar-electronics.com

On 22 Sep 2006 04:55:24 -0700, "Telstar Electronics"
wrote in
.com:

Frank Gilliland wrote:
As far as "matching problems", if you are referring to mismatched gain
in transistor pairs, that only causes harmonics. If the mismatch is
great enough to cause one transistor to run hotter than the other,
that would be due either to component failure or ****-poor quality
control.

No, I'm talking about impedance matching problems. On the input is not
a big issue... only reducing the available drive... but a mismatch on
the output is critical... and causes big problems with excessive
transistor heating... leading to premature failure.


Ok. So what does that have to do with the difference between a PCB
mounted amp and a chassis-wired amp?

Frank Gilliland wrote:
Ok. So what does that have to do with the difference between a PCB
mounted amp and a chassis-wired amp?

I think the problem here is always one of repeatability. Anyone can
fiddle around for a time impedance matching and make one amp work...
but when you plan to make a number of units... having wires running all
around, and putting components in different physical locations
unit-to-unit makes performance unpredictable. There is another problem
that shouldn't be overlooked about the wiring method... that is the
problem of manufacturability. The PCB version is usually much easier
and faster to build... not a insignificant advantage when building
numerous units.

www.telstar-electronics.com

On 22 Sep 2006 05:31:06 -0700, "Telstar Electronics"
wrote in
.com:

Frank Gilliland wrote:
Ok. So what does that have to do with the difference between a PCB
mounted amp and a chassis-wired amp?

I think the problem here is always one of repeatability. Anyone can
fiddle around for a time impedance matching and make one amp work...
but when you plan to make a number of units... having wires running all
around, and putting components in different physical locations
unit-to-unit makes performance unpredictable.


Well, you think wrong. I tried to explain this before but I guess it
didn't sink in the first two times, so let me make this -really-
simple:

http://bama.sbc.edu/

Many of those radios were (and still are) considered by many to be
some of the best ever built. If you really think their chassis wiring
construction made their performance "unpredictable" then there are
only three possible conclusions: One, that your experience is severely
limited; two, that your sanity is in doubt; and three, that you are
digging for the lamest of excuses to discredit me at the expense of
your own credibility.

I'm guessing the prize is behind door number three.


There is another problem
that shouldn't be overlooked about the wiring method... that is the
problem of manufacturability. The PCB version is usually much easier
and faster to build... not a insignificant advantage when building
numerous units.


Haste makes waste.

"Telstar Electronics" wrote in message
oups.com...
Frank Gilliland wrote:
Ok. So what does that have to do with the difference between a PCB
mounted amp and a chassis-wired amp?

I think the problem here is always one of repeatability. Anyone can
fiddle around for a time impedance matching and make one amp work...
but when you plan to make a number of units... having wires running all
around, and putting components in different physical locations
unit-to-unit makes performance unpredictable. There is another problem
that shouldn't be overlooked about the wiring method... that is the
problem of manufacturability. The PCB version is usually much easier
and faster to build... not a insignificant advantage when building
numerous units.

www.telstar-electronics.com

Point to point wiring does not have to mean the birds nest constuction you
describe. RF wiring could well be stamped out metal pieces mounted on Teflon
or ceramic. very repeatable, very stable. It could also mean the isolted pad
constuction where smalll sqares of PC board are glued to a substrate. This
has proven reliable, obviously an improvement over PC board material could
be found.and better mounting methods than glue.

There are two big problems I see with most amp designs. One is biasing, even
the cheapest Boomer would be much improved if it had an adequae bias
circuit. The other is proper setup. I doubt if someone mostly interested in
how well they can make the power meter swing will pay much attention to
setup instuctions. Attenuators on the front end would be a joke. How would
establish proper drive for a given setup with only a cheap power/VSWR meter.
FET amps really dont have a stability problem if properly designed. The idea
of using a switching power supply to take the voltage up to 50 volts or more
is a good one that has already been proven in audio amps. It is impossible
to make an amp idiotproof, just when you thingk you have along comes a
better idiot.

Jimmie D wrote:
Point to point wiring does not have to mean the birds nest constuction you
describe. RF wiring could well be stamped out metal pieces mounted on Teflon
or ceramic. very repeatable, very stable. It could also mean the isolted pad
constuction where smalll sqares of PC board are glued to a substrate. This
has proven reliable, obviously an improvement over PC board material could
be found.and better mounting methods than glue.

Yes, I agree with you. The problem is that these amp builders are not
using the point-to-point methods you describe. From what I can see...
they are gluing pieces of copper clad board (via double sticky tape) to
a non-etched copper-clad board. They have no regard for characteristic
impedance of trace widths
(http://www.pcb123.com/help/calculators/microstrip.html). I also am not
really crazy about the longevity of double-sticky tape... LOL


There are two big problems I see with most amp designs. One is biasing, even
the cheapest Boomer would be much improved if it had an adequae bias
circuit. The other is proper setup. I doubt if someone mostly interested in
how well they can make the power meter swing will pay much attention to
setup instuctions. Attenuators on the front end would be a joke. How would
establish proper drive for a given setup with only a cheap power/VSWR meter.


Agreed, my new amplifier design
(http://www.telstar-electronics.com/S...202879ABTC.pdf) now has
thermal tracking class AB biasing. I also don't use any front-end
attenuators. Like you say, proper setup is critical to any good
station. The operator needs to pay attention to the drive requirements
of the amplifier... and should adjust the driver accordingly.

www.telstar-electronics.com

On a sunny day (24 Sep 2006 07:20:57 -0700) it happened "Telstar Electronics"
wrote in
. com:

Jimmie D wrote:
Point to point wiring does not have to mean the birds nest constuction you
describe. RF wiring could well be stamped out metal pieces mounted on Teflon
or ceramic. very repeatable, very stable. It could also mean the isolted pad
constuction where smalll sqares of PC board are glued to a substrate. This
has proven reliable, obviously an improvement over PC board material could
be found.and better mounting methods than glue.

Yes, I agree with you. The problem is that these amp builders are not
using the point-to-point methods you describe. From what I can see...
they are gluing pieces of copper clad board (via double sticky tape) to
a non-etched copper-clad board. They have no regard for characteristic
impedance of trace widths
(http://www.pcb123.com/help/calculators/microstrip.html).

At 27MHz 50Ohm this is not critical.


I also am not
really crazy about the longevity of double-sticky tape... LOL

Maybe it is epoxy glue, how would you know.

Agreed, my new amplifier design
(http://www.telstar-electronics.com/S...202879ABTC.pdf) now has
thermal tracking class AB biasing.

Yes that is good.

I also don't use any front-end
attenuators. Like you say, proper setup is critical to any good
station. The operator needs to pay attention to the drive requirements
of the amplifier... and should adjust the driver accordingly.

There are many sets on the market, somebody will drive it with too much,
and somebody else will drive it with too little.

Tough world out there.
;-)

www.telstar-electronics.com

On 22 Sep 2006 04:55:24 -0700, "Telstar Electronics"
wrote:

+++Frank Gilliland wrote:
+++ As far as "matching problems", if you are referring to mismatched gain
+++ in transistor pairs, that only causes harmonics. If the mismatch is
+++ great enough to cause one transistor to run hotter than the other,
+++ that would be due either to component failure or ****-poor quality
+++ control.
+++
+++No, I'm talking about impedance matching problems. On the input is not
+++a big issue... only reducing the available drive... but a mismatch on
+++the output is critical... and causes big problems with excessive
+++transistor heating... leading to premature failure.
+++
+++www.telstar-electronics.com
**************

Mismatches only stress transisitors when they are driven beyond the
manufacturer's reccommended operating points. Like Frank said,
ampheads don't care about specifications. If a transistor is speced
for 100 watts then getting 150 watts out it is better.

james