Just got this amp for real cheap from someone local. I know it probably had issues, but it was so cheap I couldn't pass it up. So got home and hooked it up on my MFJ-891. It's showing high reflect no matter what setting I have it on. On max setting and with meter set on the 200 watt scale, both needles jump up. Left side jumps up to a little over 150watt, and the reflect side jumps up to about 50 watt reflect. This only happens with this particular amp in line. I have another amp and the reflect is fine. So the amp does key up and work, so the question is. Can a transistor go bad and still allow the amp to work to an extent, or could it be another component that has gone bad?
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Texas Star DX350HDV high reflect issue
- Thread starter CorruptHawkeyez
- Start date
not sure how to check the impedance on the amp. Is there a way i can do this with a multimeter with the amplifier off? I did check the ohm on C8 and am getting 0.5 with the meter set on 200
Shadetree Mechanic
Delaware Base Station 808
Put the SWR meter between the radio and the amp. This will show if the input needs to be tuned. This is what I did to mine.
https://www.worldwidedx.com/threads/texas-star-dx-350-hdv-input-swr.230089/#post-627003
https://www.worldwidedx.com/threads/texas-star-dx-350-hdv-input-swr.230089/#post-627003
Easy fix. Simple amplifier ......
Several things would need to be checked and verified.
Would need to be tuned on the input and output circuits.
Several things would need to be checked and verified.
Would need to be tuned on the input and output circuits.
Does it happen with a different radio?
Does it happen with a dummy load?
Does it happen with a dummy load?
You know it seems we are seeing this problem more lately with Texas Star amps.
Does your amp have Toshiba's in it or HG transistors?
73
Jeff
Does your amp have Toshiba's in it or HG transistors?
73
Jeff
There is more than one way for an amplifier to become unstable and generate extra frequencies. Odds are this is the root of your high SWR reading. The extra frequencies don't match the tuning of your antenna, and the high SWR is NOT from the signal on your channel frequency. A low reading with the barefoot radio will confirm that the antenna behaves itself with a clean signal.
The high SWR reading is the sum total of the wanted and unwanted frequencies all added together. The wattmeter can't tell them apart. So, if your SWR is high at 54 and 81 MHz for example, it should be. It's not built to accept those frequencies. And those are the most-likely harmonic frequencies for the amplifier to produce.
The SWR meter just lumps all this energy together and shows a high reading.
I would look for a mechanical cause first. Loose ground screws on the circuit board or coax sockets. A part that has come loose at one end.
Might be something more complicated, but it's best to start with the simple stuff.
73
The high SWR reading is the sum total of the wanted and unwanted frequencies all added together. The wattmeter can't tell them apart. So, if your SWR is high at 54 and 81 MHz for example, it should be. It's not built to accept those frequencies. And those are the most-likely harmonic frequencies for the amplifier to produce.
The SWR meter just lumps all this energy together and shows a high reading.
I would look for a mechanical cause first. Loose ground screws on the circuit board or coax sockets. A part that has come loose at one end.
Might be something more complicated, but it's best to start with the simple stuff.
73
It has DEI transistors.
@Mustang 131
I don't have a dummy load available, but it does happen with another radio also.
@nomadradio
I did some probing around testing some of the caps while I had it open. I did come across C3 which is very near the input (while using the schematic from cbtricks) and it has no continuity both ways with the wires. nothing, nada, zilch. If C3 was bad, what would that not allow the amp to do? Like I said though, the amp will key up and transmit, it just has high reflect and lower watts than normal.
PS, In checking some of the other caps, such as the input tuning cap, which is supposed to be .00047uF. With the setting I had set on my multimeter I got a reading of 0.5 on that cap; which I believe would be ok for that one. C3 is supposed to be a 1200pF ceramic disc type. What reading should I be getting on that one?
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OK, so I found part of the problem. on top of the stackpole there is a 1000pF stacked mica. The solder connection between one side of the pole and the ground on the stacked mica had broken lose. I soldered the mica back in and the below video is what I get now on the meter.
???
Stackpole ? Are you referring to one of the transformers ?
If that is the case, which one ? ..... Input or output ?
Stacked mica ? Are you referring to a metal clad mica capacitor on one end of the transformer on the top ?
If that is also the case, that capacitor does not solder to ground.
Stackpole ? Are you referring to one of the transformers ?
If that is the case, which one ? ..... Input or output ?
Stacked mica ? Are you referring to a metal clad mica capacitor on one end of the transformer on the top ?
If that is also the case, that capacitor does not solder to ground.
I understand what you're saying now. it may not be ground, but it does connect between the 2 sides of the stackpole. In the picture it's C14. The negative side of the mica had come lose.
