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Adjusting the Ameritron ALS-1300 Power Supply voltage

Discussion in 'Amplifiers' started by dxhound, Jan 28, 2011.

  1. dxhound

    dxhound Active Member

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    How much voltage drop is there at full output? 50v is nominal, What does it dip to?
    Also looking at this http://www.datasheetcatalog.org/data...com/MRF150.pdf There apears to be some play room with 300 watts disipation per device and they seem like they would tolerate a little more voltage. Any chance there is an adjustrment for Power supply voltage? It would be nice to see this amplifier achieve 1500w. I know theres not much diff.....but since you get to play with it!



    AHhhhh EHAM is littered with ALS-1300 issues like this one!
     
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  2. Toll_Free

    Toll_Free Active Member

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    300 watts of DISSIPATION means about half that in CLEAN output.


    Meaning, 150 watts each. OUTPUT. Not a whole lot of room to spare.

    It's not a CB amp, it's not running bipolars, and it won't like being overdriven to make the meter go farther to the right.

    You want a REAL solid state amp? Get a prometheus, by Dishtronix :) 10 grand gets you a 2400 watt OUTPUT amplifier. ALL BAND, ALL MODE, ALL DAY!

    I've had problems with mosfet devices when being run BELOW Pout (saturated). In talking with people at Galaxy, it seems when people turn their mosfet amps / radios DOWN, they start having problems, like blown devices. Of course, those are "switchmode' rf amplifiers, and this uses actual RF rated devices, so might not be the problem.

    --Toll_Free
     
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  3. dxhound

    dxhound Active Member

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    Typically these amps run 55%-60% efficiency. And Im sure they are not reaching anywhere near their thermal maximum where Po begins to suffer. Im not saying blast 200 watts into the thing, but somthing like 110 watts. I just want to know does it stay linear with increased input or does it begin to flatten out. Because if it begins to flatten out the gain is dropping and you are now turning the transistors into expensive heaters. Also the reports Ive been seeing say the Power supply sags to 45 volts under load. If this is true, the power supply may be replaced with a better unit and stay at 50-52 volts. That alone could easily cost you 100-200 watts output. I know it will never make a diff on the S meter, But I figure what the hey, We all like to tinker!
     
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  4. Moleculo

    Moleculo Administrator Staff Member

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    There is no adjustment indicated in the power supply schematic. I looked around inside the supply and didn't see anything that jumped out at me. There may be something in there somewhere, but I'm didn't find it.
     
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  5. HiDef

    HiDef Active Member

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    Someone told me these were being Built by Fatboy for Ameritron.

    They seem to have the same color solder so maybe there's somthing to it.
     
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  6. Captain Kilowatt

    Captain Kilowatt Professional Amateur Staff Member

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    I was wondering how long it would be before this came up. :cry: There is a lot more to how much power you can get out of a device then simply what the power dissipation is.
     
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  7. dxhound

    dxhound Active Member

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    Hence the SOME part, I would never try anything on my own amp like this, but since he gets to play a little bit, we might as well have some fun.

    And if each transistor produces 150watts Po and the amplifier is 60% efficient, with a dis. rating of 300 there is some wiggle room. and thats taking into account loss in the output combiners and filters.

    The voltage adjustment I was asking about isnt to VOLT the amplifier per say. But instead have the amplifier stay closer to its rated voltage under load instead of sagging so much.
     
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  8. Toll_Free

    Toll_Free Active Member

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    The increase in IMD will completely offset any increase in Pout you would see.


    I mean, let's blow up a thousand dollar amplifier to get another 100 watts on the meter?

    You want the amp to not sag, build a better power supply, DON'T increase the dissipation the transistors are having to deal with. Remote monitor the voltage on the collectors and then feed that back to the regulator, as linear supplies do....... THEN, you don't have the 'fluctuating voltage' issue... Otherwise, ANY voltage fluctuation causes IMD and can cause other issues as well.

    I'm failing to follow your math, anyway. If each transistor is capable of 300 watts of diss., then that equates to 180 watts output at 60 percent eff. THEN, take 10 percent off for the xformers, oh wait, another 10 percent off for the COMBINER, and you're right back at.... Oh hell, 180 * .8 = 144 watts OUTPUT for each transistor, TOTAL OUTPUT for the stage.......

    Whoops. It's that physics that f*cks CBers up every time :(

    Also, on a FET, voltage plays a HUGE issue. To have 50 volts on a FET, in amateur service (where 1:1 VSWR is NOT always the norm), you better have devices capable of 200 volts, MINIMUM.... I'd go 250 or better.. There MIGHT be a reason Ameritron isn't running their amplifiers balls to the wall... Or Alpha... Or THP, or any other manufacturer besides CB junk. BUT, back to the original meaning, if you increase that voltage so the FET sees 50 volts across it, and have any VSWR, it could mean bye bye fets.

    I KNOW Yeasu had issues with this exact thing in the radio I own.....



    --Toll_Free
     
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  9. Captain Kilowatt

    Captain Kilowatt Professional Amateur Staff Member

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    I was just simply saying that I knew someone would bring it up at some point. It always does. One thing a lot of people do not understand is that some devices have a maximum power output that they can produce regardless of how much power they can dissipate. This especially true of RF power modules and all increasing the power supply voltage does is lower IMD and increase power dissipation.
     
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  10. dxhound

    dxhound Active Member

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    If IMD is a consideration in this discusion then the amplifier should never produce more than 640 watts to stay within the confines of the FCC's -43db IMd requirement. Now we know the Filters better the final IMD numbers, but since I dont know their roll off points and attenuation, I cant comment on their ability to reduce IMD. We only assume that they have a Q of 12. And if built well, the filter network should only present a .5db loss in total output. Then there is negative feedback that will drop the gain, however this can be over come with more drive. Roughly 5-6watts per device for 150 watts at 30mhz

    Also the mrf-150 can withstand upto a 30:1 SWR without any degradation in Po. So if it can withstand that kind of current abuse at full output, then It will def. handle more Po with only a 1.5:1 SWR.

    On the discussion of the transformer and combiners. The broad band transformer offers a Q of unity and there for the IMd suppression is negligible as well as Power loss.. The combiner if tuned correctly should present a 50Ohm load and again loss would be negligible. Even if it presented a 3:1 SWR the loss would be 1.25db.

    So providing SWR is in line and kept minimal there will be little to no iron loss in the cores of the transformers and cores of the combiners adding to the efficiency of the amplifier.

    AGAIN!!! I know fully that the extra 150-200watts will produce no diff at the rxing station, I just want to know if the amplifier is BEEFY enough to have some headroom. Just look at my Ten Tec 425 Titan, Rated at 1500watts butt capable of 3kw. within IMD specs upto around 1900. There is what the amp was designed for, and what it can do!

    I agree, the power supplies current rating should be addressed to prevent voltage loss, But adding 6% to 8% in voltage will not add much stress.

    Oh, and I spend Very little time on 11 meter compared to 80-40meter...10-4

    This device has exhibited linearity upto 190watts with little trouble, Ill find the article and post it.
     
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  11. Moleculo

    Moleculo Administrator Staff Member

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    I don't know how you came up with that number. I have a copy of the IMD specs and tests on this amp and it does very well. I was planning on posting the results as soon as I get a working amplifier back.
     
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  12. dxhound

    dxhound Active Member

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    The IMD rating I was referring to was taken from the mrf150 datasheet. Thats not taking into account Ameritrons filter network.
     
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  13. Moleculo

    Moleculo Administrator Staff Member

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    Well then you can't say "...the amplifier should never produce..." An amplifier is incomplete without its filter network. I'm mean, we're not talking about CB amps here :D
     
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  14. dxhound

    dxhound Active Member

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    Your right, I was in the discusion with toll free about the device itself and then about the amplifier as a whole. Without knowing the Q of the filters, I have no clue how hard you could push the amp before killing the overall IMD. Im guessing no matter what, its better than an sb220. They were never required to meet IMD specs since they were a kit. I think I heard best IMD product was -35db. FCC requires 43db.
     
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  15. Toll_Free

    Toll_Free Active Member

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    I had to stop reading at that point, as your output filters (no filtering, actually) can reduce in band IMD, which is what people get pissy about.

    Apples and Oanges.

    Who CARES that the device can do 190 watts output cleanly. It's not DESIGNED for that. I can get 4000 watts out of a single 8877, too. BUT IT ISN'T DESIGNED FOR THAT!

    Please, do a bit more research.

    --Toll_Free
     
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