Question about SSB Biasing.

[Rhinoky]

I ran across a page that sells the Base style amplifiers and the wording has got me confused. All the amps I look at say AM-FM-SSB for modes at the bottom, however the wording is a little different in the discription. For instance, Some say SSB biased, and some say SSB bias and delay. Take these two ads...

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Carl Built 1.2KW Base HG2879​

$2,099.99

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Add To Cart

Carl Built 12xHG2879 Base

Do you remeber the O.G. X-Force amps? The ones that NEVER gave a issue? Well he is back! Carl Built amps are here to stay. Top quality, Great Customer Service, and a name you can count on!
HERE----> Here is the Carl Built 1.2KW Base. It sports 12 HG2879 Transistors, SSB delay AND Preamp.

Allow up to 2 weeks for delivery

Specifications:

AC Voltage: 220V
Dead key input: 20-40 watts
Max pep swing input: 400 watts PEP
Dead Key output: 600w max
Output power: 2800-3200 watts PEP
Mode: AM-FM-SSB
SWR requirements- 1.5 or less



And this one,

Carl Built 1.0KW Biased base​

$1,999.99

Choose 110V or 220V
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Add To Cart

Carl Built 10xHG2879 Biased Base

Do you remeber the O.G. X-Force amps? The ones that NEVER gave a issue? Well he is back! Carl Built amps are here to stay. Top quality, Great Customer Service, and a name you can count on!
HERE ----> Here is the Carl Built 1.0KW Base. It sports 10 HG2879 Transistors, SSB delay AND Biasing, Preamp.

Allow up to 3 weeks for delivery

Specifications:

AC Voltage: 110V or 220V
Dead key input: 5-15 watts
Max pep swing input: 300 watts PEP
Dead Key output: 400w max
Output power: 2500-3000 watts PEP
Mode: AM-FM-SSB
SWR requirements- 1.5 or less

30 Day warranty on everything except the transistors


These are from Truck CB sales, a link to the page: https://truckscbsales.com/cb-radio-products/carl-built-base-amp-1.0kw


Is this just miss-wording and they are the same, or are there a difference with the word biasing listed on the one amp? I do realize there are two more pills on one amp but it's only $99 higer wich leads me to believe there may be a difference with the word "biasing" after all.

Thanks,

RR

 

[nomadradio]

Here's the difference. The transistors used in these amplifiers can be switched on by just the radio's AM carrier alone. And if all you care about is AM, this simplifies the design. No need to turn off the power to them when receiving, they turn themselves off when there is no AM carrier feeding into them. Also allows you to drive the transistors harder and get a bit more wattage from them. This is commonly referred to as "Class C", or "AM only".

Sideband is different. No carrier. As a result, the transistors must be switched "on" when the amplifier's relay closes or the sideband audio will be terribly scratchy and distorted. A circuit that keeps the RF power transistors turned on while the relay is activated is called a bias circuit or bias supply. It adds complexity and expense, so a builder who caters to AM operators will leave it off.

Just one problem. To use a self-contained amplifier on sideband you need a delay in the relay circuit. Something to keep it keyed for a second or so between words and syllables. With no steady AM carrier to hold the relay closed, it would chatter with every syllable unless this delay feature is added. The switch on the front panel labeled "SSB" will activate this delay.

You'll see this on an amplifier whether or not there is a bias circuit to keep it from sounding like doo-doo on SSB. The delay is cheap to add, and gives the impression you can use it for sideband without necessarily spending the money to do it right. Plenty of AM-only amplifiers built out there with that "SSB" switch on the front.

73

 

[Rhinoky]

Thanks Nomad, you explained it well. That's what confused me... they all have the SSB on the front .. so I didn't know the difference except one said SSB delay and biasing one said SSB delay. Thank you for your time.

73's

 

[sp5it]

AM also need biasing. Otherwise amp is not linear and produces distorted signal.
Only FM it doesn't.
Mike

 

[BC Coyote]

AM also need biasing. Otherwise amp is not linear and produces distorted signal.
Only FM it doesn't.

Which is exactly why the vast majority of CB type amps are "splatter boxes".
Non-linearity in an amp = distortion and splatter.

 

[575nightrider]

Here's the difference. The transistors used in these amplifiers can be switched on by just the radio's AM carrier alone. And if all you care about is AM, this simplifies the design. No need to turn off the power to them when receiving, they turn themselves off when there is no AM carrier feeding into them. Also allows you to drive the transistors harder and get a bit more wattage from them. This is commonly referred to as "Class C", or "AM only".

Sideband is different. No carrier. As a result, the transistors must be switched "on" when the amplifier's relay closes or the sideband audio will be terribly scratchy and distorted. A circuit that keeps the RF power transistors turned on while the relay is activated is called a bias circuit or bias supply. It adds complexity and expense, so a builder who caters to AM operators will leave it off.

Just one problem. To use a self-contained amplifier on sideband you need a delay in the relay circuit. Something to keep it keyed for a second or so between words and syllables. With no steady AM carrier to hold the relay closed, it would chatter with every syllable unless this delay feature is added. The switch on the front panel labeled "SSB" will activate this delay.

You'll see this on an amplifier whether or not there is a bias circuit to keep it from sounding like doo-doo on SSB. The delay is cheap to add, and gives the impression you can use it for sideband without necessarily spending the money to do it right. Plenty of AM-only amplifiers built out there with that "SSB" switch on the front.

73

Very well explained, thanks for taking the time to do it so well!

 

[AudioShockwav]

Transistor PA Bias Circuits

This is a very good primer about Bias in rf amps.

73
Jeff

 

[9C1Driver]

With Carl built you can request a class B bias if you plan on doing SSB.

 

[Shockwave]

Operation within the transistors rated specifications, becomes much more important when they are run in the biased, linear mode. Bias causes a portion of the transistors dissipation, to be consumed at DC, rather than RF. All bias power can therefore only be dissipated as added heat within the transistor junction.

This is how a linear is supposed to work and not something to be alarmed about. Just don't expect the same drive levels, voltage limits, or maximum output power that a lower quality class C amplifier might handle or produce.

 

[nomadradio]

Class C is "hot rod" mode. Just remember what happens to a hot rod when it takes Dead Man's Curve a little too fast one time too many.

73

 

[linearone]

Speaking of drive, simply stated, a biased amplifier takes less drive than an unbiased one.

 

[dave457]

Then again class "c" is more efficient than a/b or b

 

[linearone]

Then again class "c" is more efficient than a/b or b

Yup. People forget that gain and efficiency are separate things

 

[brandon7861]

I'm not trying to troll here, in fact, I made this mistake myself here not long ago, so don't take this the wrong way, but I think the 11m world, amp builders included, have been calling amplifiers by the wrong class. If it has a transformer with a grounded center tap having a transistor working each side of it, that's not class C, regardless of whether it has additional bias or not.

Every single piece of amplifier literature I have ever come across shows that when you have two transistors, one working as the waveform goes positive and the other working when the waveform goes negative, that is called class B, regardless of presence of bias. Class C is when you are conducting for only a portion of the positive going part of the waveform and absolutely nothing during the negative portion, like the final (or paralleled finals) in a galaxy 959. When you put two class C amps together that work both the positive and negative parts of the waveform, it is, by definition, no longer class C, even though it would appear as such from the perspective of each individual transistor. When you see two transistors working a common transformer, suggesting one is working each half of the waveform separately, that is class B. Plain old class B. Now, If you took that and applied bias such that each transistor is nearly turned on, that's called class AB.

Maybe I am wrong, or maybe every single person that ever did a write up on the differences between amplifier classes is wrong. I'll let you guys decide. I just feel that not getting this right makes us 11m guys look silly.

Fire away, I can take it

Edit: I think the only way an amplifier working both halves of the waveform could be called class C is if the incoming signal established a negative DC voltage at the base to further reduce the duty cycle beyond what the transistor's diode drop alone would cause. Please correct me if I am wrong here.

 

[AudioShockwav]

Go to School on RF Power Amplifier Classes - Mini-Circuits Blog

Learn about the differences in how Class-A, B, AB, C and other classes of solid-state power amplifiers (SSPAs) are biased and how they perform with respect to linearity, efficiency and output power.

blog.minicircuits.com

This is a very good read about the different classes of rf amps.
I think you are getting confused by push/pull operation and actual classes of bias.

73
Jeff