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Message |
    
Captian_radio
Intermediate Member
Username: Captian_radio
Post Number: 178
Registered: 9-2004
| | Posted on Tuesday, April 10, 2007 - 9:26 pm: | 
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Here's the problem , Amp turned on and the audio seems very distorted.This amp has a pair of PT9797A's in it,radio is a Trc 485, wattage is around 2 watts am,tried wattage lower and it won't key the amp, turned it up and it keys the amp but the audio still stinks ,adjusted the audio level still the same results,tried it on base as well as in the car,swr is very good with it on ,1.3,tried various mics still the same,power supplies well filtered and regulated .The audio has that typical nasal or rough sound .Believe it or not it even has proper output filtering.What can I do to clean up the audio?
Robert L. Spicer
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Romstar
Member
Username: Romstar
Post Number: 85
Registered: 3-2007
| | Posted on Wednesday, April 11, 2007 - 12:01 am: |
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The filtering is messed for the frequency you are operating on.
Or, Or, Or......
The transistors are messed up inside and about to fail.
Those are your two options.
Romstar |
Captian_radio
Intermediate Member
Username: Captian_radio
Post Number: 180
Registered: 9-2004
| | Posted on Friday, April 13, 2007 - 8:18 am: |
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Tnx for the reply Romstar,I see that you are also in Nova Scotia.
About your reply on my amp,you mentioned that possibly the TR's are on the way out,I was wondering how you came up with this conclusion ? It is an older mobile amp and I believe the problem may be the amount of drive to the input of the amp.I haven't installed it in the car yet,waiting for some fine weather which as you know here in Nova Scotia could be a long way off yet.I have 3 different mobile radios to try it out on and hopefully one of them will be compatible with the amp.
Bob CEF451
Robert L. Spicer
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Romstar
Member
Username: Romstar
Post Number: 91
Registered: 3-2007
| | Posted on Friday, April 13, 2007 - 10:53 am: |
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Well, if you have an audio problem with an amp, it basically boils down to one of two possibilities.
1. The amp isn't tuned to operate in the frequency range you are using. It may be close, which simply requires tuning to that band, or it may have been "tweaked" by someone who doesn't know how to tune them. Read that as randomly compressing and expanding coils, twisting variable caps and other general silliness.
2. The transistors are being driven out of their linear operating range. This results from only two possible choices. The first being that they are over driven. Since you said you are using 2 watts, that isn't the case. So that brings us to the second option. Someone DID overdrive the thing, and it messed up the transistors, and as a result, they are no longer capable of amplifying a signal in a linear fashion.
Some other possibilities come to mind. Supply current may not be sufficient to properly run the amp. Previous operation or mis-treatment has caused one or more support components to fail, resulting in poor operation.
In all of these cases however, the end result is the same. Something is preventing the amp from operating in a close to linear fashion, and distorted or garbled audio transmission is the product.
In my experience, it is most commonly a failure of the transistors. Yours may be fine, but regardless I would check everything.
I know what you mean about the weather. I managed to get a couple of mobile radios, but I really don't feel like pulling the car into the garage to do the install. So, I wait for the nice weather. Might make a day out of it with the wife. Pack what I need in the trunk, find a nice field somewhere, and have lunch and hook up a radio. Makes for a happy wife, and a cleaner install.
Good luck,
Romstar |
Captian_radio
Intermediate Member
Username: Captian_radio
Post Number: 181
Registered: 9-2004
| | Posted on Monday, April 16, 2007 - 1:16 pm: |
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Well I think I have found the problem with the audio with the amp on. I have found that the radio that I am using it with has the mic attenuator removed.It sounds fine on AM because I can control the audio gain , but on SSB it not adjustable, so I am going to replace the limiter and see how it works . Hopefully this will clear up the problem with audio on SSB . I will post my results when I replace the limiter.
Bob CEF451
Robert L. Spicer
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Romstar
Member
Username: Romstar
Post Number: 96
Registered: 3-2007
| | Posted on Monday, April 16, 2007 - 5:21 pm: |
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How did SSB perform with just the radio and no amp? Were there problems running barefoot?
Romstar |
Captian_radio
Intermediate Member
Username: Captian_radio
Post Number: 184
Registered: 9-2004
| | Posted on Tuesday, April 24, 2007 - 9:59 pm: |
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Romstar, I hooked the amp up in the car today and so far it seems to work very good.I was about 20 miles away from home in an area and was surrounded by hills. I checked with a local station who said I was giving only an S1 signal , with amp on it jumped up to S6, audio was very good on AM and SSB but only with the car running. I checked it with others and they say the audio is sounding very good. The preamp works quite well also enabling me to dig the low signals out of the noise. So what can I say but so far so good.I have it wired direct to the battery and both leads are fused with 15 amp fuses. I guess its a wait and see situation.
Bob CEF451
Robert L. Spicer
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Romstar
Intermediate Member
Username: Romstar
Post Number: 100
Registered: 3-2007
| | Posted on Wednesday, April 25, 2007 - 10:23 pm: |
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Excellent. Glad to hear it working properly now.
Romstar |
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