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UK CB Radio Specialists - Expert Advice, Competitive Prices & knowledgeable staff, Est 1996
< Menu > CB Accessories > Amplifiers    <- Go Back
   Product #1975   
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One of our favourite amplifiers of all time, they've been around years and are a well proven design using two MosFET transistors (MS1307's) offering both efficiency and reliability.

The 737 is rated as being able to handle 10w of input power, however for safe working and for a life-cycle measured in years rather than months i would not put any more than 7w into one of these.

This amplifier can be used on FM, AM and SSB modes (the legal CB system in the UK uses FM only) and it features an electronic switch so unlike some amplifiers you do not need to choose which mode you are using.

    SIZE :
  • 108 mm Wide
  • 44 mm High
  • 85 mm Deep (excluding sockets on the back)

  • Large on/off push button switch
  • Red LED "on" light
  • Internally fused (6.3amp)
  • Frequency range : 26-30 MHz
  • Normal expected output : 50w, Max output : 80w

It's worth studying the power output graph image above... this shows that you will get different power outputs depending on the supplied voltage.

Normal alternator output is 13.8v so if wired directly to the battery with it's own seperate power feed (the best way) you'd expect this amplifier to be receiving about 13.6v. If you are stationary with the engine off it would be receiving approx 12.0v

Looking at the graph you can see that with a 4w input (legal CB's put out 4w) you'll get around 40w output at 12.6v (approx 35w at 12.0v) but nearer 50w output at 13.6v. A good illustration of why it's best to wire this amp (and all amps) directly to the battery.

This amplifier has nuts inset into either side which can slide forwards and help you secure it on a bracket or whatever, although no bracket is included.

All in all, probably the most reliable amplifier currently available. I (Jim, the owner of Communication Eleven 4x4CB and webmaster of this site) have run a couple of these amplifiers for many years in the past [ not now of course - use a totally legal setup now! ;-) ] and can i vouch for them.


  • CONSTANT POWER SUPPLY : This amplifier must have power to it all the time it is in line - if you don't want it on just use the on/off switch, but if it is in line it MUST have power to it otherwise the relay will close when the power feed is removed and the transmit power from your CB will not be allowed through, causing damage to both the CB and amplifier.
  • AMPLIFIERS GET HOT : The majority of the size of these amps are the heat-sink fins on the top - the job of these is to get hot as dissipate the heat into the air, and they will get pretty hot in use. You need to make sure that there is a free flow of air around these amps - best not to cram them into a small space.
  • YOU NEED A LOW SWR TO USE AN AMP : One of the quickest ways to kill an amplifier like this is to run it into an antenna system that has a high swr... like the CB's we sell, the output transistor (the bit that can get damaged by a high SWR) is NOT covered by the guarantee as it's the user/installers responsibility to make sure the SWR is low - ideally below 1.5 although you can usually get away with readings upto 1.7 / 1.8 if amplified transmissions are kept short. More about SWR on our SWR explained page.
  • BE CAREFULL WHERE YOU USE AN AMP LIKE THIS : Please do not use this amplifier is you are within 100 yards of the following : petrol pumps, police/ambulance/fire vehicles or other cb users on the same or adjacent channel to you. You may also find that this amp can set off some older domestic wireless house alarms as well as cause interference/breakthrough on televisions and radios - maybe best switched off when driving through a housing estate for example... leave the amp for the countryside!
  • AMPLIFIERS ARE ILLEGAL : Remember Amplifiers like this are illegal to use on CB Radio. A lot of people do use them, and prosecutions are extremely rare and even then only when serious interference or abuse has occured, but please be mindful of their illegality.
  • A WORD ABOUT HOW INCREASING OUTPUT POWER WORKS : When using an amplifier, double the power does not mean double the transmission distance. For every half a signal point increase at the receiving radio you need to double your power, so the largest gains are made fairly low down the scale :

    For Example :
    If someone is receving you at signal 5 when you are using 4w, they'd get you at signal 5.5 with 8w, signal 6 with 16w, signal 6.5 with 32w, signal 7 with 64w, signal 7.5 with 128w, signal 8 with 256w etc etc.

    So you can see that using this amplifier will give you approximately a 1.75 signal pont increase - however this does rely on their signal meter being calibrated which most aren't really so the actual gains you'll see may differ slightly depending on who you're talking to.

    You can also see that if you were running a 250w amplifier, increasing this to 500w will only get you 0.5 signal point increase - the same as going from 4w to 8w !!

    Consequently the differences in actual amplification of signal between this amp giving around 50w output and some of the others we sell which give about 85w, is small.

This item is listed in CB Accessories > Amplifiers

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