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All things being equal: AB vs C

Class C conduction angles are too low to produce reasonable output distortion levels in R.F. linear service.

Some amp builder's smoke and mirrors include suggestion that they have some kind of new technology. They Don't.

Shifting conduction angle during the R.F. cycle isn't a viable technique when linearity is concerned.

You can't fight physics. The rules have not changed since the 1930s.

Even class B amplifiers need degenerative feedback to become good R.F. amplifiers.

You want to see a meter swing higher, use class C and plenty of drive. Some operators are all about watching a wattmeter when they transmit.

You want audio that doesn't sound like you are talking through a kazoo, use class AB or B. There will of course be a lot more device heat to deal with.
 
Last edited:
HiDef said:
Class C conduction angles are too low to produce reasonable output distortion levels in R.F. linear service.

Some amp builder's smoke and mirrors include suggestion that they have some kind of new technology. They Don't.

Shifting conduction angle during the R.F. cycle isn't a viable technique when linearity is concerned.

You can't fight physics. The rules have not changed since the 1930s.

Even class B amplifiers need degenerative feedback to become good R.F. amplifiers.

You want to see a meter swing higher, use class C and plenty of drive. Some operators are all about watching a wattmeter when they transmit.

You want audio that doesn't sound like you are talking through a kazoo, use class AB or B. There will of course be a lot more device heat to deal with.
Click to expand...

And this is not a real issue if the operator is responsible and does not drive the device into saturation as with any device and the heat will be as minimal as it is in class-c and I am living proof of that statement.
 
mackmobile43 said:
And this is not a real issue if the operator is responsible and does not drive the device into saturation as with any device and the heat will be as minimal as it is in class-c and I am living proof of that statement.
Click to expand...


Class B by definition uses a larger conduction angle than class C. This alone even without any drive power will increase device heat dissipation.

Keeping within the subject asked by the original poster [not exceeding manufacturer's ratings, AM service] saturation isn't an issue. We can't saturate anything and stay within manufacturer's recommended parameters.

You cannot amplify AM in a linear fashon without about 2 times as much wasted heat as carrier out in a 100% sine wave modulated system.

Example for a 1 KW DC input linear amplifier

1000 watts consumed from the power supply will give you about 300 watts carrier out to the antenna. 700 watts goes up as wasted heat. Most of that dissipates in the transistors or tubes. A small amount is lost in the tank circuit and wiring.

300 carrier watts out of a linear on AM, almost 700 watts of heat on the fins.

That 300 carrier watts equates to 1200 P.E.P. watts. Notice it looks like we are making power out of thin air. 1000 watts DC gives us 1200 P.E.P. watts out to the antenna. That's where the old defacto "twice average DC" input specification used in ham amps comes from. That 1 kw DC input is an average and it maxes out at 2000 watts where we have peak efficiency of 60 percent giving us 1200 P.E.P. watts out with about 800 watts going up as heat.

If you lower the conduction angle to save heat the amplifier will no longer be linear. Linear means you can draw a straight intercept LINE on a graph that plots device grid or base swing verses plate or collector swing. It's in the book. My explaination is too short.

No free lunch.
 
Wish I could add more to this thread but IM sitting in the back of the class waiting patiently for more. :thumbup: .......but then again , maybe there isn't anymore ? :( Enjoyed the read HiDef
 
HiDef said:
Class B by definition uses a larger conduction angle than class C. This alone even without any drive power will increase device heat dissipation.

Keeping within the subject asked by the original poster [not exceeding manufacturer's ratings, AM service] saturation isn't an issue. We can't saturate anything and stay within manufacturer's recommended parameters.

You cannot amplify AM in a linear fashon without about 2 times as much wasted heat as carrier out in a 100% sine wave modulated system.

Example for a 1 KW DC input linear amplifier

1000 watts consumed from the power supply will give you about 300 watts carrier out to the antenna. 700 watts goes up as wasted heat. Most of that dissipates in the transistors or tubes. A small amount is lost in the tank circuit and wiring.

300 carrier watts out of a linear on AM, almost 700 watts of heat on the fins.

That 300 carrier watts equates to 1200 P.E.P. watts. Notice it looks like we are making power out of thin air. 1000 watts DC gives us 1200 P.E.P. watts out to the antenna. That's where the old defacto "twice average DC" input specification used in ham amps comes from. That 1 kw DC input is an average and it maxes out at 2000 watts where we have peak efficiency of 60 percent giving us 1200 P.E.P. watts out with about 800 watts going up as heat.

If you lower the conduction angle to save heat the amplifier will no longer be linear. Linear means you can draw a straight intercept LINE on a graph that plots device grid or base swing verses plate or collector swing. It's in the book. My explaination is too short.

No free lunch.
Click to expand...

I see your point, thanks CCM.
 
Interesting place to put my first post ... But i'll try ...
:unsure: Are we missing the fact that someone keying a radio is finally heard ...Considering the playing field isn't any gun an equalizer ? no matter how many innocent bystanders get killed ..?? and really who of us is really all that innocent here ??
 
linearone said:
How did I miss this? This is a really good post.

that amp is apparently ok right?
Click to expand...

That amp is almost identical to the used one I sold a month ago that had the popped relay.

I haven't looked at too many 10-12 meter amps lately, but that's about as clean as they come.
 

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