What is the function of a variable....

[SmackDown]

in a two transistor linear without a third transistor as a driver? All the linears I've come across with a variable control has had a driver in front of the finals. All the linears I've seen that do not have drivers may have a switch that goes from low power to high power.
Will the variable on a two pill for example, do the same without some loss?


3's

 

[dxhound]

All these variables do is bleed off a certain amount of rf from your radio to ground. they are just variable resistors. You can install them in any solid state amplifier as long as the input is kept at 50 ohm.

 

[9C1Driver]

in a two transistor linear without a third transistor as a driver? All the linears I've come across with a variable control has had a driver in front of the finals. All the linears I've seen that do not have drivers may have a switch that goes from low power to high power.
Will the variable on a two pill for example, do the same without some loss?


3's

There are dozens of 2 pill amplifiers that have either a variable power control, a hi, lo, or a lo med hi. Texas Star 250,350,400, and 500 HDV amps, Magna Force 100,200,and 400, X-Force, Davemade, Fatboy's all make 2 pill variables.

 

[SmackDown]

My question is directed at the wisdom of using a potentiometer with either a carbon "wipe" or a wire "wipe" instead of a switch which is a more mechanical connection for changing the output of a linear.


3's

 

[wulff]

I might be wrong but I don't believe the amps use a pot to run the RF to ground, this would be bad on the the finals and overheat them.
I believe the hi/low switches works by cutting voltage down to the voltage regulator.
Why do you not want a hi/lo switch? Are you just looking for more control over it (the output)?

 

[dxhound]

I might be wrong but I don't believe the amps use a pot to run the RF to ground, this would be bad on the the finals and overheat them.
I believe the hi/low switches works by cutting voltage down to the voltage regulator.
Why do you not want a hi/lo switch? Are you just looking for more control over it (the output)?

The RF from the radio enters the amplifier. Then, a piece of wire or coax carries the RF to either a potentiometer or a switched resistor bank that is attached to ground. some rf passes to the driver or final of the amplifier, some is bled off to ground. These are primitive ways of implementing what is known as a swamping network.

There are no voltage regulators used, un less the amplifier has a true bias network. But changing that voltage would only net a change in class. A, C, AB1 etc...

 

[Crusher]

A carbon type is used. Never a wirewound. A variable is used with a resistor in series and a resistor shunted to ground. While cheap it works well as long as proper wattage rating is used otherwise it heats up and you can watch the carrier drift as components heat up.