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Adjusting the Ameritron ALS-1300 Power Supply voltage

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  #1  
Old 01-28-2011, 04:57 AM
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Default Adjusting the Ameritron ALS-1300 Power Supply voltage


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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Old 01-28-2011, 07:47 AM
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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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Old 01-28-2011, 08:44 AM
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Quote:
Originally Posted by Toll_Free View Post
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
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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Old 01-28-2011, 09:19 AM
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Quote:
Any chance there is an adjustrment for Power supply voltage?
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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Old 01-29-2011, 11:14 AM
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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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Old 01-29-2011, 11:33 AM
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Quote:
Originally Posted by dxhound View Post
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!

I was wondering how long it would be before this came up. 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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Old 02-01-2011, 12:58 PM
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Originally Posted by Captain Kilowatt View Post
I was wondering how long it would be before this came up. There is a lot more to how much power you can get out of a device then simply what the power dissipation is.
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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Old 02-01-2011, 04:32 PM
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Quote:
Originally Posted by dxhound View Post
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.
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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