I'm getting the klv 550 amp back today. the person say's the amp works fine but when he tries to set the SWR'S he says everything goes haywire. the swr meter goes all over the place and cannot be set.Gets about a 7 to full scale reading. I have to figure out why this is happening. the relays might be keying where they shouldn't be. or a cap. might be shorted near the relays. If anyone has an idea what might be wrong I would really like the help. Thank you ,Ron
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KLV 550 Amp
- Thread starter Ronald Porter
- Start date
don't know of any driver. this is two transistors, sd1407 finials.there is a transistor,nte152 that is heat sinked real good. this is an audio transistor. don't know if its a driver. Is this what you are talking about? Ron
I told the person the same thing,but he said when he takes it out of line the swr's go back to normal.. I got it back to make sure it was in tune to peak as good as I could get it with the adjustments inside the amp. It could be a little out of harmonic and cause distortion. All I can do is check it over and see if it is working well. thanks, RonThere are no SWR adjustments on this amplifier. The other possibility is a bad jumper cable or a bad pot on the external SWR meter.
Kind of proves my point? If he takes all of the other stuff out of the circuit it all works normally. There are no user adjustable filtering circuits on the circuit board. If there is a problem it's in the test equipment.
Do check the SO-239 mounting hardware and be sure it is tight and the connections are properly made.
You might want to learn a little about SWR, harmonics, and what a driver is before messing amplifiers.
Rich
Rich
Put a good-quality low-pass TVI filter between the output of the KLV and the SWR meter.
The SWR reading will now fall back to more or less what it shows with only the barefoot radio transmitting.
The higher reading is not really SWR. Not at the frequency you're using, anyway. The high SWR reading is caused by harmonic frequencies generated by the amplifier. These multiples of 27 MHz, 54, 81, 108 MHz are NOT what the antenna is tuned to accept. As a result the RF energy at those frequencies is pretty well reflected back down to the meter 100 percent. Just a few Watts of harmonic energy will fool the SWR meter. It can't tell one frequency from another. It can only read the sum-total power of all the frequencies coming out of the box.
Just why the amplifier is producing a lot of harmonic energy is another question. Don't know. I do know that this model includes only the tiniest amount of harmonic filtering in its output circuit.
My best guess would be that the two RF transistors are not in balance. Could it be that one of them blew out and was replaced alone? This would produce an unequal gain on each side of the push-pull circuit and get you a lot of harmonic energy. One benefit of using matched pairs in a push-pull amplifier circuit is that it reduces harmonic output.
If you have a TVI filter handy, just try it. And if you don't have one, don't worry. The high SWR reading is a symptom of other things going on, not necessarily a sign of antenna or feedline problems.
73
The SWR reading will now fall back to more or less what it shows with only the barefoot radio transmitting.
The higher reading is not really SWR. Not at the frequency you're using, anyway. The high SWR reading is caused by harmonic frequencies generated by the amplifier. These multiples of 27 MHz, 54, 81, 108 MHz are NOT what the antenna is tuned to accept. As a result the RF energy at those frequencies is pretty well reflected back down to the meter 100 percent. Just a few Watts of harmonic energy will fool the SWR meter. It can't tell one frequency from another. It can only read the sum-total power of all the frequencies coming out of the box.
Just why the amplifier is producing a lot of harmonic energy is another question. Don't know. I do know that this model includes only the tiniest amount of harmonic filtering in its output circuit.
My best guess would be that the two RF transistors are not in balance. Could it be that one of them blew out and was replaced alone? This would produce an unequal gain on each side of the push-pull circuit and get you a lot of harmonic energy. One benefit of using matched pairs in a push-pull amplifier circuit is that it reduces harmonic output.
If you have a TVI filter handy, just try it. And if you don't have one, don't worry. The high SWR reading is a symptom of other things going on, not necessarily a sign of antenna or feedline problems.
73
Besides what Nomad stated, you might want to try a low pass filter between radio and amp. It's possible that radio is a generating a lot of harmonics and the amp is just amplifying it. What radio are you using to excite this amp?
Good point, Crusher.
That amplifier is incredibly easy to overdrive. Trying a lower setting on the amplifier's input knob will reduce that high SWR if the radio is overdriving the amplifier.
73
That amplifier is incredibly easy to overdrive. Trying a lower setting on the amplifier's input knob will reduce that high SWR if the radio is overdriving the amplifier.
73
Thanks, tried this, did not work. I didn't even plug it in, put it in line to dummy load, set the swr meter, keyed the little radio I've been using and it pegged the meter. there is something going on with this amp for sure. checked for voltage reading at a 12 volt reg. diode and got -5.5 volts on both sides of the diode. got this reading on other places on the board. It put out 250 watts on key up with 31/2 watts drive. but sometimes the relays stick and won't release,have to shut it done to release the relays.
I don't know where the -5.5 volts is comeing from, but something is going to ground.
Getting 35volts to collector on the finials, but not getting good readings anywhere else. There are to sets off relays one 12 volt and one 28 volt. one might be stuck open causing backwards readings?? this amp has been worked on before I received it. the 12 volt power supply part of this is not even hooked up, the voltage regulator ic isen,t there. there is no voltage even going to that section of the board. I think this thing was toasted at one time with to much input power and cooked the board someplace. These double sided circuit boards are difficult to work on as it is,then have something like this one.I'll keeping looking might get lucky. Thanks for all the help, slowley loosing hope for this project. there is much more wrong with this than he says. Ron
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