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?