Driving the Amp ?

[Tripple Nickel]

B) When I use my Amp (2 pill) B) either on HI or LO, locals tell me I'm driving my amp too much. My 148 gtl dead keys between 4-5 watts, what am I missing here ? Is that why some only carry 2 watts dead key ? I just don't want to mess up my radio. Should I look for a tube amp with LOAD/PLATE tuning, a Contex like I had back in the 70's ? What am I missing here.
555

 

[W5LZ]

Try thinking of it like this. Any/all amplifiers have a maximum usable input power level, you can't go over that without problems. Most solid state amplifiers don't require much input power. And since the typical output from a stock radio tends to be something around 5 watts (total, not dead key), that's what most of them are designed for. Thinking in terms of dead key doesn't take that maximum input power into consideration. So, an over driven amplifier isn't unusual at all. What's unusual is convincing someone that they shouldn't be driving the snot out of the thing. That maximum usable input power isn't dealing much with popping a transistor, it deals with the quality of the output signal. There's quite a bit of 'spread' between blowing something up and producing 'quality'. More does not mean better.
- 'Doc

 

[hotrod]

B) When I use my Amp (2 pill) B) either on HI or LO, locals tell me I'm driving my amp too much. My 148 gtl dead keys between 4-5 watts, what am I missing here ? Is that why some only carry 2 watts dead key ? I just don't want to mess up my radio. Should I look for a tube amp with LOAD/PLATE tuning, a Contex like I had back in the 70's ? What am I missing here.
555

a 2 pill amp usually 1-2 watt dead key and 12-15 watt swing. OR what i do is use the
variable on my radio so the amp keys around 100 watts on the high setting ,then
let it swing from there.

 

[RatsoW8]

Maybe the CB community is getting hip to the fact that driving an unfiltered amp to its maximum isn't necessarily the best way to make friends with your neighborhood ham or avoid distortion and band splatter?

 

[Tripple Nickel]

On the backside of the Amp is a sticker stating 4 watt input. Does the pre-amp being on or off have any effect ?
555

 

[KM3F]

We don't know your amplifier specs.
Here is what your missing:
Dead key is the carrier only.
100% modulation added to the carrier would be a 'peak drive' of 20 watts if the dead key were 5 watts or 5x4=20.
If this overdrives the amplifier on peaks there will be distortion and splatter.
You have to understand the principle of the operation.
The amplifier gain spec has to be known or an accurate honest input /output power specified or you don't know what you need to do for correct drive.
.
Here is an example:
On a 30 watt in/160 watt out, FM could be used at the full 30 watt drive.
But to use this same amp on AM the drive has to be dropped all the way down to 7.5 watts carrier because 7.4 x 4 = 30 watts max drive the amp will take at 100% modulation.
Where did the #4 multiplier factor come from?
It's normal AM modulation science that 100% modulation is equal to 4 times the carrier power.
If an amplifier is driven harder it goes into gain compression causing distortion, splatter and excessive harmonics.
Some possible problems adding to distortion are a mismatch between the radio and amplifier and mismatch at the antenna.
This very often shows up as RF getting back into the mike line because your whole setup becomes RF hot on the outside.
You need to sort out the drive level first then be sure the matches are all less than 2 to 1 SWR.
On CB, lack of this knowledge brings about a lot problems that are not understood.
Good luck.

 

[9C1Driver]

On the backside of the Amp is a sticker stating 4 watt input. Does the pre-amp being on or off have any effect ?
555

The pre-amp is recieve only, it will have no effect. They can put anything on a sticker, the bottom line is you are dead keying way too much into that small amp. This is why people you talk to can tell you are over driving it. What they hear is audio that has a pinched up sound, almost starting to garble.

What kind of amplifier is it and what finals are inside? As an example a local guy used to run a Texas Star 350 years ago with a Galaxy 88 tuned for a 2 watt dead key on Low and 8 on Hi. He talked for quite some time and sounded superb with the setting on Lo. Then he decided he was really gonna impress everyone and run it on Hi..........since his amp was a HIIII DRIIIIVE. It sounded like crap, all pinched up.........he was over driving the amp with too much carrier. That is what you are doing too. Easy fix, back the dead key down to 1-2 watts.

 

[9C1Driver]

a 2 pill amp usually 1-2 watt dead key and 12-15 watt swing. OR what i do is use the
variable on my radio so the amp keys around 100 watts on the high setting ,then
let it swing from there.

Depending on the 2 pill amp 100 watts dead key out might even be too much. I usually try to set the amp input so the amplifier on Hi will dead key 1/4 to 1/3 of the peak output.

 

[The Bruce]

B) When I use my Amp (2 pill) B) either on HI or LO, locals tell me I'm driving my amp too much. My 148 gtl dead keys between 4-5 watts, what am I missing here ? Is that why some only carry 2 watts dead key ? I just don't want to mess up my radio. Should I look for a tube amp with LOAD/PLATE tuning, a Contex like I had back in the 70's ? What am I missing here.
555

Don't push more than 2 watts into your low-drive amplifier.

 

[Tripple Nickel]

We don't know your amplifier specs.
Here is what your missing:
Dead key is the carrier only.
100% modulation added to the carrier would be a 'peak drive' of 20 watts if the dead key were 5 watts or 5x4=20.
If this overdrives the amplifier on peaks there will be distortion and splatter.
You have to understand the principle of the operation.
The amplifier gain spec has to be known or an accurate honest input /output power specified or you don't know what you need to do for correct drive.
.
Here is an example:
On a 30 watt in/160 watt out, FM could be used at the full 30 watt drive.
But to use this same amp on AM the drive has to be dropped all the way down to 7.5 watts carrier because 7.4 x 4 = 30 watts max drive the amp will take at 100% modulation.
Where did the #4 multiplier factor come from?
It's normal AM modulation science that 100% modulation is equal to 4 times the carrier power.
If an amplifier is driven harder it goes into gain compression causing distortion, splatter and excessive harmonics.
Some possible problems adding to distortion are a mismatch between the radio and amplifier and mismatch at the antenna.
This very often shows up as RF getting back into the mike line because your whole setup becomes RF hot on the outside.
You need to sort out the drive level first then be sure the matches are all less than 2 to 1 SWR.
On CB, lack of this knowledge brings about a lot problems that are not understood.
Good luck.

Thank you......KM3F and 9C1DRIVER, this makes a lot of sense the way you put it, I understand, it's been a while guy's, over 40 yrs ago. Technology has changed, modulation is the same, Amps were much different then, you could adjust for it. I got you loud and clear, I'll try and figure it out without going into my radio, it goes in the motorhome, I'm also looking for a nice Base station. Thanks again, 3's to you and yours.
555

 

[9C1Driver]

You should be able to adjust VR10 in your 148 to get a lower dead key, on SSB a Cobra 148 should not overdrive a 2 pill amp. If you are concerned VR11 is the SSB power adjustment, something like 12-14 watts PEP will be fine.

 

[hotrod]

Depending on the 2 pill amp 100 watts dead key out might even be too much. I usually try to set the amp input so the amplifier on Hi will dead key 1/4 to 1/3 of the peak output.

yes i agee. figured though was good starting point.

 

[The Jerk]

I've got a 2-pill (2x2879) behind a Uniden PC76XL...

I drive it with the variable all the way down, about 3/4 of a watt dead key input, and 4 or so watts peak. That gives me around 50 watts of dead key and about 200 watts of peak from the amp.

A two pill takes almost nothing to drive it correctly...and as previously stated, it also depends on the amp (type of transistors and/or input padding).