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TS DX500V, convert to class C?
- Thread starter dxing440
- Start date
B
BOOTY MONSTER
Guest
Ya got that right.
Even DaveMade, Midnight Special, and the other amp brands now offer to bias their amps to AB so they don't lose customers to Texas Star.
As you know C class amps were intended to run on FM mode by design; not AM.
IIRC, most of the CB AM only radios run Class B output. Should run a Class B amp; think that Midnight Special amps builds them that way. Most SSB/CB radios are AB Class outputs. Also, an AB Class amp for a CB/AM only radio is an improvement overall. They might run a little hotter and draw more amps than a Class C but should put out just as much power. While offering little in the way of spurs and harmonics. Of course, this is all moot if the radio is running more than 100% modulation . . .
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Nah homie, convert that thing to class Sextouple Z
it will put out 10.4567 trillion watts with only 0.0001 watt input
it will put out 10.4567 trillion watts with only 0.0001 watt input
Wow, I thought you were just being funny when I first saw this. Dude, your amplifier is fine and the quality of the audio will be much smoother then any class C box. Class C can sound blarring and harsh most of the time. Just turn the SSB delay switch off and run it on AM.
The fact is, Your Texas star already is class C. Ever notice after you talk on it for awhile, it seems to produce a lil more power than it did when it was cold. The reason for this is, the bias circuit is not thermally tracked/corrected.
We all learned in high school that electrons move more freely when the medium heats up. Well, because the bias in these amplifiers is nothing more than a resistor, with no diode regulated power supply, The resistor heats up and begins to change value.
This in turn causes the bias supply voltage to drop from the AB region into class C.
So, if you want to convert your Texas Star 500 into class C, just talk on it for about 5 minutes until shes nice and hot......then watch the smoke roll(PUN INTENDED)!
We all learned in high school that electrons move more freely when the medium heats up. Well, because the bias in these amplifiers is nothing more than a resistor, with no diode regulated power supply, The resistor heats up and begins to change value.
This in turn causes the bias supply voltage to drop from the AB region into class C.
So, if you want to convert your Texas Star 500 into class C, just talk on it for about 5 minutes until shes nice and hot......then watch the smoke roll(PUN INTENDED)!
the increase in output for a given input as the amp heats up is due to increased conduction in the transistors,
as the transistors heat up they conduct harder, operating point moves up towards AB not down towards class C,
if the bias voltage was dropping more than is needed to counteract the increased conduction of the transistors output would drop not increase,
a thermal tracked bias supply is used to counteract the rising conduction of the transistors with rising temperature to maintain a constant operating point/stop thermal runaway,
if the bias supply source impedance is not sufficiently low the bias voltage will sag with increased drive level causing a drop in operating point towards class C, your modulation will modulate the bias supply,
class C having better efficiency than AB is only true when both amps are designed with correct load lines for the supply voltage and operating point they are using,
when used on stock voltage, class C amps of the davemade style draw more current per watt of output than any properly design class AB amp i ever came across because they are designed with load lines for running elevated voltage in keydowns,
the often touted class C efficiency advantage in this example is a fairytale, they have very poor efficiency when used on stock voltage,
it gets even worse if the clone builder throws a resistive divider + untracked diode bias circuit in there to keep the ssb crowd happy,
another one for cb mythbusters.
as the transistors heat up they conduct harder, operating point moves up towards AB not down towards class C,
if the bias voltage was dropping more than is needed to counteract the increased conduction of the transistors output would drop not increase,
a thermal tracked bias supply is used to counteract the rising conduction of the transistors with rising temperature to maintain a constant operating point/stop thermal runaway,
if the bias supply source impedance is not sufficiently low the bias voltage will sag with increased drive level causing a drop in operating point towards class C, your modulation will modulate the bias supply,
class C having better efficiency than AB is only true when both amps are designed with correct load lines for the supply voltage and operating point they are using,
when used on stock voltage, class C amps of the davemade style draw more current per watt of output than any properly design class AB amp i ever came across because they are designed with load lines for running elevated voltage in keydowns,
the often touted class C efficiency advantage in this example is a fairytale, they have very poor efficiency when used on stock voltage,
it gets even worse if the clone builder throws a resistive divider + untracked diode bias circuit in there to keep the ssb crowd happy,
another one for cb mythbusters.
B
BOOTY MONSTER
Guest
you know that ain't gonna jive with the needle watching , splatter box owning all knobs to the right crowd .... 
but heck even going from 200 watts pep to 500 pep didn't give me a significant difference down the road and i didn't make any skip contacts with 500 watts that i couldn't make with 200 . i was surprised how little effect even slightly more than doubling my power had on my TX distance .
but heck even going from 200 watts pep to 500 pep didn't give me a significant difference down the road and i didn't make any skip contacts with 500 watts that i couldn't make with 200 . i was surprised how little effect even slightly more than doubling my power had on my TX distance .
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The conduction angle does change in the transitor allowing for higher outputs. But the fact that the bias voltage drops due to heat, is what pushes these amps into class C when they get hot.
Monitor the current consupmtion and peak output when the amplifier is cold. Then, using the same amount of drive, monitor the current and peak output.
You will notice one of two scenarios. The amplifier produces more power with the same or less current draw, or the amplifiers output stays constant and the current consumption drops. Ive done this with a TS350 and 500V, and both amplifiers went from a low 70% efficiency to high 70, low 80% region.
This was measured using an inline current meter, LP100a and IFR1600
