Sufficent drive for amp

[Cookie Monster]

I have a Commstar TX-150 AB Linear, however have not hooked it up. Antenna today hopefully. It has high & low power settings, and all I have is a 12 amp power supply.
If I use a basic P=E x I, it wouldn't be big enough at 150W being 12.5Amps for my radio too. Just curious if anyone else ever used this model before and knows what it drew on high & low power settings.
Thanks for the response 9C1 Driver.

 

[Captain Kilowatt]

I have a Commstar TX-150 AB Linear, however have not hooked it up. Antenna today hopefully. It has high & low power settings, and all I have is a 12 amp power supply.
If I use a basic P=E x I, it wouldn't be big enough at 150W being 12.5Amps for my radio too. Just curious if anyone else ever used this model before and knows what it drew on high & low power settings.
Thanks for the response 9C1 Driver.

You didn't factor in the efficiency which is typically 50%. 12.5 amps times 13.8 volts is 172 watts. Mulitply that by the efficiency and you get around 84 watts output. Fudge a little and call it good for 100 watts out. Probably 90% of CBers negate to account for efficiency when considering current required for a given power output or vice versa. 12 amps average or 20 amps peak is required to operate a normal 100 watt amateur radio in SSB mode.

 

[Onelasttime]

If you go by the spec sheet you need 8-10 watts pep for each 2SC2879. I would tend to disagree with this practice and say you need have that in rms input. Than you have to take the input padding into account. You have to look at the matching network. Your amp is not close to AB bias unless it is being feed from a low impedance source so if you doing the typical resistor bias on a high power BJT.

In a really good design you should be able to get 300 watts rms from a 4 transistor amp driven by a stock CB. I can tell you right now you will not see that from any of the "builder's" amps or from any of the gray market CB linears. This is why they almost always parade their peak number's out for people and show it with all the swing with insane amounts of input drive like a 2 transistor amp feeding a 4 transistor amp.

It has been my experience that CB amps put out about half as much power RMS as they should when talking about clean output.

Your amp setup is likely well under 50% efficiency. You need to make current and voltage are in line with the amount of drive power your putting in. RMS power really likes voltage and current to be readily available.

 

[Captain Kilowatt]

If you go by the spec sheet you need 8-10 watts pep for each 2SC2879. I would tend to disagree with this practice and say you need have that in rms input. Than you have to take the input padding into account. You have to look at the matching network. Your amp is not close to AB bias unless it is being feed from a low impedance source so if you doing the typical resistor bias on a high power BJT.

In a really good design you should be able to get 300 watts rms from a 4 transistor amp driven by a stock CB. I can tell you right now you will not see that from any of the "builder's" amps or from any of the gray market CB linears. This is why they almost always parade their peak number's out for people and show it with all the swing with insane amounts of input drive like a 2 transistor amp feeding a 4 transistor amp.

It has been my experience that CB amps put out about half as much power RMS as they should when talking about clean output.

Those specs are for PROPER operation at the given IMD specs. Sure you can get more out by driving the piss out of the devices but then that throws all the other performance specs out the window. Manufacturers spec their devices for proper RESPONSIBLE operation. CBers with a don't care attitude can certainly get more out but there is a balance between can and should.

Your amp setup is likely well under 50% efficiency. You need to make current and voltage are in line with the amount of drive power your putting in. RMS power really likes voltage and current to be readily available.

50% is pretty close for the typical non-class C amplifier. Maybe a little more like 55%. Class C could be as high as 70% or more depending on devices used and actual construction.