Dan,
Your speaking of a capacitor in paralell with a resistor on the emitter to
ground? The resistor sets the bias and the capacitor is used as a bypass cap.
Sometimes, an emitter resistor can be the signal output instead of the
collector. A coupling cap will be between the resistor and emitter to the next
stage. There though, they wouldn't be a bypass cap and it's according to the
circuit use. An inductor on the collector is generally used to block the signal
from getting into the power supply. Generally, they'll be an inductor, and
between it and the collector, a coupling cap to the next stage the same as a
tube amps tank circuit starts really. The base bias is generally made up of two
resistors. One going to ground, and one to the VCC, making a voltage divider.
The previous stage is coupled to the base through a coupling cap also in an amp
circuit, which blocks the base bias voltage off the previous stage. An
oscillator will be different, but the oscillators bias can be changed
. There's two ways to bias a transistor amp circuit I've seen, either base, or
base and emitter bias. The only ways to raise the gain would be to change the
bias, use a transistor with higher gain than the one now in use (more E to C
current for the same amount of B current), or increase the bases drive signal.
That's really true of any amplifier circuit. Hope that helps.
Best,
Will
*********** REPLY SEPARATOR ***********
On 3/15/06 at 9:15 PM Dan Sawyer wrote:
>Thanks Will,
>
>One quick follow up:
>
>Can the RF gain of a stage be inductor collector and capacitor emmiter
>biased transistor be changed by varying the capacitor value?
>
>Thanks - Dan
>
>Will Matney wrote:
>
>>Dan,
>>
>>Increasing gain can be had by resetting the bias if the transistor can
>stand the extra current through it. Also, you have to watch and not
>overload the stage ahead of it. However, you said it did better with about
>4X extra drive. You would want to select a transistor that will withstand
>the amounts of current needed for the gain, and that it's frequency spec
>will match. Then re-do the bias so you acheive the gain with (or without)
>a new transistor. I'd check what the transistors specs are that's in there
>now. You may find it can handle it by doing the math. If it wont, look for
>one that will. Try looking through the Motorola books, etc. You might even
>be able to use a NTE, etc., replacement by crossing the original, and
>finding one similar but a little stronger.
>>
>>Best,
>>
>>Will
>>
>>
>>*********** REPLY SEPARATOR ***********
>>
>>On 3/15/06 at 6:59 PM Dan Sawyer wrote:
>>
>>
>>
>>>All,
>>>
>>>I have an older transistor based transceiver. I have separated the
>>>circuit and substituted an external signal generator in place of the
>>>internal circuit. The circuit drives a mixer, by varying the amplitude
>>>the mixer performs better with about a 4x increase in drive.
>>>
>>>My question is: what is the best way to increase the output of an
>>>amplifier stage?
>>>
>>>Is it as simple choosing a transistor with a higher beta?
>>>
>>>There are two nearly identical stages. Both are NPN, the collector bias
>>>is a resistor - inductor in series and the emitter circuit is a
>>>capacitor - resistor in parallel. Would reducing the resistor values
>>>increase gain?
>>>
>>>If this question is too general - where is a good source for reading
>>>about stage gain variables?
>>>
>>>Thanks - Dan
>>>_______________________________________________
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>>>http://lists.contesting.com/mailman/listinfo/amps
>>>
>>>
>>
>>
>>
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>>
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