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Amp selection

Discussion in 'Amplifiers' started by Ben Hebert, May 13, 2018.

  1. Ben Hebert

    Ben Hebert Active Member

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    i have a general hp40. Would I be able to add a amp with this radio? If so how do I choose a amp?


     

  2. nomadradio

    nomadradio Analog Retentive

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    That radio is pretty large. Delivers roughly twice the power of a legal 40-channel CB.

    Goes without saying that this requires an amplifier that's built to match a transmitter twice the power of a CB radio.

    A radio with a built-in "driver" amplifier like a Texas Star DX667V has one RF power transistor that drives a set of four. A radio this size has nearly the same drive power as that built-in driver stage in that amplifier. You'll assasinate it with this radio.

    A "straight" 4-transistor amplifier is pretty much the smallest you can hope to use. The Texas Star DX500 would probably hold up okay.

    Most other "straight" 4-transistor or 8-transistor should sound okay with this radio. Yes, using one twice the minimum size will work. They tend to last a lot longer running at half or 2/3 throttle. A 4-transistor amp will be in high gear all the time. One with eight transistors will cost more to buy and cost less to own if it takes longer to break down.

    This kind of amplifier is still contraband, and the folks who sell them may or may not honor a warranty if it's bought new.

    And if it's used, never hand over the money before you see what a wattmeter reads with your radio driving it.

    Another side effect of the "black-market effect" is that nobody installs overload protection in a CB amplifier. Drives up cost, doesn't make it sell better, so they leave it out.

    This produces a lively market filled with blown-out amplifiers offered for sale. Like a car in that front yard with the For Sale sign and weeds grown up around it. "Just needs a battery, you can drive it anywhere".

    Hence the advice to see for yourself that a used one works before the seller is out of reach forever.

    Just stay very far away from any amplifier that has a driver amp in it.

    73
     
    Shadetree Mechanic likes this.
  3. Ben Hebert

    Ben Hebert Active Member

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    Could I go bigger than the Texas star dx500
     
  4. nomadradio

    nomadradio Analog Retentive

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    That was the point I wanted to make.

    A bigger amplifier may only be getting half or 2/3 of the drive it can accept with this radio. This means it won't blow up as soon as an amplifier that's always at the red line, all other things being equal. Running an amplifier below its limits is not going to cause any problem.

    JUST SO LONG AS IT ** DOESN'T ** HAVE A BUILT-IN DRIVER STAGE.

    Your radio is big enough to make an internal driver a bad idea.

    Which is the other point I wanted to get across.

    73
     
    Shadetree Mechanic likes this.
  5. 543_Dallas

    543_Dallas Sr. Member

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    Is this going to be a base or mobile setup? Do you prefer transistors or tubes?
     
  6. Ben Hebert

    Ben Hebert Active Member

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    Base setup. its my first time using an amp
     
  7. 543_Dallas

    543_Dallas Sr. Member

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    Base is good. That gives you some more options. A 100 watt radio will work well with most of the tube type ham amplifiers. One will probably cost more than a cb amp but you'll have a cleaner signal and they aren't too hard to operate.

    The first thing that comes to mind is a drake l4b. The ameritron al80b is good for 125 watts am carrier and 700 pep. People buy them then upgrade to a legal limit amp so you can easily find a used one.

    If you want to go transistors I'd find something with 6 or 8 2sc2879s then after you get a power supply the tube amp may have been cheaper. Make sure your antenna and coax are up to snuff before putting the fire in the wire.
     
    sunbulls likes this.
  8. Ben Hebert

    Ben Hebert Active Member

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    Oh ok thanks
     
  9. Ben Hebert

    Ben Hebert Active Member

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    Any certain brands better the rest? And not quite as pricey?
     
  10. 543_Dallas

    543_Dallas Sr. Member

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    What's the price range? You usually get what you pay for. If you buy something quality the first time and take care of it the cost of ownership is low. If you buy something cheap it could nickel and dime you for years.

    I know guys that have been beating on sweep tube amps for years and buying tubes every year or so. They would have saved a lot time and money if they had bought quality.

    Whatever you do don't buy something that you have to abuse to get the power you want. If you find an amp you want look at the parts it's built with and find out what are the transistors or tubes capable of. How hard they are to find and how much replacement will cost.
     
  11. Ben Hebert

    Ben Hebert Active Member

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    I wanna try and stay under 800.00 if possible
     
  12. Shadetree Mechanic

    Shadetree Mechanic 808 On The North Side of Dover

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    I know it is hard to figure out what you want and what will work with what. I have learned a lot in my short time here and I am still learning. I think the hardest part about running an amp is to know when something is wrong with the system. If you buy used, you could buy someone else's problem but if you know amps then this might be the best value. Tube amps add another level of complexity as you have to learn how to adjust the Tune and Load knobs on the front. Its not hard to learn but you don't know what you don't know. Even if you get a new amp, it is possible that the input will need to be tuned for your radios output. Maybe someone with more knowledge can elaborate on that. I would start out with a small simple system like a Texas Star 500 and then upgrade it from there. If you look at the increase in signal by going with more power, it gets expensive real quick for the small increase you would get. If you still want something bigger then check this out.
    You could get something like this for around $600.
    http://www.jokermanelectronics.com/tnt-1200hd/
    [​IMG]

    Product Description
    Transistors 6x 2SC2879pp100
    ALL box come in silver color now!! No longer in Black
    Dimensions H 4 3/4' x L 11' x W 6 3/4'
    Amp Draw (maximum) 120
    Class B
    SSB Delay yes biasing
    Pre-amp yes
    Driver Required TNT 250 (optional)
    Power Output (RMS) 400 Watts
    Power Output (PEP) 725 Watts
    Driven Power (RMS) 650 Watts
    Driven Power (PEP) 1200 Watts
    install recommended with 2ga wire
    and 125a fuse. Max input carrier of
    25w or 450w max carrier from amp.
    Max peak input 350w

    I have had my eye on this one for some time. It is class B so it would work well on side band as it is cleaner than the class C that most amps are. If you are not worried about SSB then a class C would be fine and possibly save a few $. This amp would need a power supply and I would run three of the Mega Watt 50a in parallel. Model S700-12. They are $110 each.
    http://megawattpowersupplies.com/
    [​IMG]
    Hope this helps.
    Chris 73s
     
    9C1Driver likes this.
  13. 543_Dallas

    543_Dallas Sr. Member

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    I used to recommend xforce but the last 2 I've had my hands on were not the quality they once were. I don't make a habit of repairing amplifiers so I really don't see that many. The 2 pill that works as it should but the heatsink fins are facing the wrong direction for proper air flow. A 6 pill tnt that had issues because some caps were left off of some of the sections that caused an imbalance.

    The 6 pill was built in the same case that a 4 pill should be built in. Everything is crammed into a small enclosure and the bias and premp circuits were complete rats nests. So many people are building the same amp and the prices have been pushed down so far that someone that builds a good product can't afford to compete.

    For $800 I would go with an amp with one or two 3-500z tubes but a tube amp may not be right for you. A healthkit sb220 is a popular one you just have to take it easy on AM because the hv power supply and cooling system were designed for ssb use. It will still a much better amp than a 6 pill can ever be. The Drake L4B is a better option IMO.

    Keep an eye on the classifieds. You never know what will pop up.

    https://swap.qth.com
     
    Shadetree Mechanic likes this.

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