Need ALS-600 Amp Info - Elmers Forum at eHam.net

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eHam.net Forum : Elmers : Need ALS-600 Amp Info

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Need ALS-600 Amp Info	Reply
by N9VX on August 9, 2004	Mail this to a friend!
I am looking for info on the Ameritron ALS-600 amp. Some people get full power out with 50 watts or less drive. I must drive mine with about 100 watts to get full power out. If you know how to adjust or modify the amp to get full output with less drive, please email me. Note: not looking for theories, but experience. Thanks, Joe N9VX

RE: Need ALS-600 Amp Info	Reply
by K0BG on August 9, 2004	Mail this to a friend!
I've played with two units. Both required just about 65 watts for full output. You can drive them with 100 watts, apparently without damage, but the IMD is through the roof. In other words, you have to be careful not to overdrive them. ALC helps, but it isn't a cure. Alan, KØBG www.k0bg.com

RE: Need ALS-600 Amp Info	Reply
by WB2WIK on August 9, 2004	Mail this to a friend!
I've serviced ALS-600s before and am quite familiar with this product. What is your exciter (model)? Do you have the ALC line connected? If so, how did you adjust the ALC control on the ALS-600? Did you measure input VSWR (between exciter and amp)? If so, what is it, on the band(s) where it takes 100W to drive the amplifier? Also, what are you using to determine that it takes 100W drive power? The panel meter on the ALS-600 or something else? What does the power output indicate when driven with 50W? My experience with the ALS-600 is that 50W will drive it to almost "full power," but not quite. Increasing drive power from 50W to 100W creates about another <1 dB output power (like 650W out with 100W drive, and 550W out with 50W drive), indicating obvious non-linearity that would be best avoided. As such, I always kept the drive down to 50W PEP, and the output down to about 550W PEP (varies a bit by band) and kept the amp in the more linear region. Nothing to be gained by increasing output power 0.7 dB and increasing distortion at the same time. If yours is not behaving that way, but doing something differently, tell us about that. WB2WIK/6

RE: Need ALS-600 Amp Info	Reply
by W4VR on August 9, 2004	Mail this to a friend!
Joe: I bought one about 3 years ago. I had the same problem, especially on 40 meters driving with as much as 100 watts I could not get more than 400 watts output. I talked to Mike Ennis of Ameritron and he said they ship these amps out with a heavy duty swamping resistor in the input so people don't blow up the amp with 100-120 watts of drive. He sent me a different swamping resistor and that allowed me to drive the amp with much lower power and improved the output on 40 meters up to 500+ watts. You may want to give him a call and get the details...the replacement resistor is free if your amp is still under warranty. Ron, W4VR

RE: Need ALS-600 Amp Info	Reply
by WIRELESS on August 9, 2004	Mail this to a friend!
There is a series resistor between the change over relay and the rf input to the amp board. It is 35 ohms at 50 watts. You can short it out and your drive should go down. RF power transistors can have very different gain factors and can vary more than 3db. Yours may have low gain rocks in it.

RE: Need ALS-600 Amp Info	Reply
by WIRELESS on August 9, 2004	Mail this to a friend!
Forgot to add that 35 ohm resistor is R301.

RE: Need ALS-600 Amp Info	Reply
by N9VX on August 9, 2004	Mail this to a friend!
Answers: I drive the amp with a Pegasus. No ALC. No SWR between radio and amp. Meter in amp and external Palomar are about the same, also have has a Autek and VSD. 50w in 325w out. 75w in 5oow out. 100w in 600w out. I recently changed the swamping resistor from 45 ohms to 35 ohms, this helped some. (got from Ameritron) The in/out varies some from band to band, numbers based on 20 meters into a dummy load. Mike at Ameritron cautioned against going real low on the swamping resistor. Hope I did not miss something!! Joe

RE: Need ALS-600 Amp Info	Reply
by KZ1X on August 9, 2004	Mail this to a friend!
Gee. From your description, it sounds more like the power supply is 'funny.' I don't like that cross-needle meter! Can you measure the loaded voltage and current? The power draw is a dead giveaway about the 'health' of the amp.

RE: Need ALS-600 Amp Info	Reply
by KZ1X on August 9, 2004	Mail this to a friend!
Gee. From your description, it sounds more like the power supply is 'funny.' I don't like that cross-needle meter! Can you measure the loaded voltage and current? The power draw is a dead giveaway about the 'health' of the amp.

RE: Need ALS-600 Amp Info	Reply
by WB2WIK on August 10, 2004	Mail this to a friend!
Maybe the power supply is dropping out of regulation, but if it can achieve 600W output power with 100W drive, probably not. It only needs to deliver 30A at 40Vdc to hit that power. Maybe the transistors in your particular amp have less than normal gain, who knows? I never had to change the series resistor from the stock value, whatever it is (45 Ohms?). The fact that they install this resistor in fuse clip type mounts may be an indication that they do change them at the factory, though! Why not connect the ALC line, since you're using a Pegasus, it's 100% compatible. I'd give that a try, you never know. With the "dynamic ALC" in the AL80B, for example, PEP power almost always increases as soon as the ALC is connected, even while restricting peak grid current. WB2WIK/6

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