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Re: Low Power Output

 

Hello Bob,
?? I tend to think you have a problem with the amp.? If you continued to run it with 40 watts of drive on RTTY it should continue to produce 1kw until it overheats and shuts down at 100 degrees C.? This will be proven if 40 watts drive on SSB only produces 500w peak.? Usually, when one of the two LDMOS chips fail hard, (usually short on the input side of the chip)? the output drops to near zero, but there could be a failure mode on one chip that still allows half output if the input isn't shorted.?? I would contact Palstar by phone and let them know that the unit is only putting out 500 watts in any mode regardless of drive power and I'm sure he'll make it good.? If 40 watts of drive (in any mode) is only giving you 500 watts then there is an issue. ? Typically, with any manufacturer of LDMOS amps, you will likely get an entirely new RF block rather than replacing just one transistor. (guessing here)?
?? Sorry you're having this issue.? It's always a disappointment when an exciting new piece of equipment has a problem.? I use mine daily and for the first time today I hit 100 degrees C on a long AM transmission.? Normally that wouldn't be an issue with the 260ish watts of AM carrier, but I live at 9,000 feet where cooling efficiency is severely compromised.? When the temperature came down to around 70C or 80C (about 30 seconds or less) the amp operation returned to normal.? It continues to run 1kw with 40w drive. ? I'm friends with a gal who runs a traffic net for 5 hours a day working it hard the entire time.? She has one of the first LA-1K's off the production line, it's still running fine.? Of course, this could be a defective chip from the factory for it to fail so soon.? All of the above comments are based on the assumption that one of the chips has failed, there could be an issue with a combiner, LP filter, combiner, relay, etc... even the coax used in the transformers.? They will be able to diagnose it quickly.
Good luck and let the group know how it works out.
Best,
Dennis

On 9/20/2018 at 1:19 PM, "Bob KU5J" <valentines.49@...> wrote:
I just acquired a new LA-1K yesterday, and put it in service that evening.? At first, with 35 watts drive in RTTY, the unit showed output on the LA-1K watt meter plus an MFJ watt meter that I have of near 1000 watts. In fact, with 40 watts drive, the unit was showing well over 1KW output.? Over the next ten minutes, I ran some on the air tests, and the unit performed perfectly, showing output of 1KW or more.? However, after that short time, it quit putting out the higher power. Instead, with 40 watts output using RTTY,? the output dropped to only 500 watts on? both meters. I tried using two different radios on several different bands, and the result was the same.? SWR as shown on the LA-1K was in the 1.2-1.6 range. I do use a tuner after the amplifier to keep SWR in control.? I did all these tests with the ALC line unplugged.? With a voltmeter, I verified the supplied operating voltage was? 235-240 volts. Vd on the LA-1K stayed steady at 50, and Id varied a little, but was always near 23.? I tried turning the amplifier on and off and all sorts of other "tests" to see if it would start to read 1KW again, but it never did go higher than 500 watts.? I also tried transmitting with a straight key on CW, and on CW key down, it showed the same output as RTTY did. At no time did I drive the amplifier with over 50 watts.?

I email Paul at Palstar, and he told me RTTY output is only 500 watts, so that's what I should expect it to show.? But, the unit was showing a solid 1KW when I first powered it on.? And, on CW, the specifications in the manual indicate the output is 1000 watts, not 500.? Yet, in both RTTY and CW, I am only getting readings of 500 watts.

My question is, do I have a problem?? Why would the amplifier first show 1000 watts out, and then moments later, drop to half that?? I did email Paul at Palstar back, but so far, no response.?

Thanks,
Bob KU5J
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