Cobra 148 gtl DX same power on all modes
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Cobra 148 gtl DX same power on all modes
Morning all,
Wondering if anyone has any advice on an issue I have with an old 148 gtl dx.
Symptom is SSB and AM/FM are all roughly the same power output.
The ALC control does work, as does everything else really, just can't get more than whatever I set AM as for SSB.
The radio was a auction site scrappy special, parts or not working, and when it arrived, the AM/FM was cranked to max (maybe this fault was already present), final blown, and regulator not too happy either.. so replaced them and now AM can be turned up to 9 watts or more, so think all that stuff is healthy.
I did read about a fault with a burned out track that can cause this symptom after a reverse polarity, but I don't think this radio has had that and I can't see any burned tracks or components.
Is anyone aware of this fault and have any areas to take a look at?
Cheers
Wondering if anyone has any advice on an issue I have with an old 148 gtl dx.
Symptom is SSB and AM/FM are all roughly the same power output.
The ALC control does work, as does everything else really, just can't get more than whatever I set AM as for SSB.
The radio was a auction site scrappy special, parts or not working, and when it arrived, the AM/FM was cranked to max (maybe this fault was already present), final blown, and regulator not too happy either.. so replaced them and now AM can be turned up to 9 watts or more, so think all that stuff is healthy.
I did read about a fault with a burned out track that can cause this symptom after a reverse polarity, but I don't think this radio has had that and I can't see any burned tracks or components.
Is anyone aware of this fault and have any areas to take a look at?
Cheers
- cb4ever104
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Re: Cobra 148 gtl DX same power on all modes
What's the voltage on the collector of the driver/final on SSB ? You should have about 5V on AM/FM and 13.8 on SSB .
30TM060
Paul aka "Sammy". (108) PY60 Old Paisley DX Group (RIP Rab Markie)
Ex GM0 , now EA5 .
Handle "Fortune Hunter" back in "the day"
Radios ....? Anything that says "TAIWAN R.O.C" on the back.
Paul aka "Sammy". (108) PY60 Old Paisley DX Group (RIP Rab Markie)
Ex GM0 , now EA5 .
Handle "Fortune Hunter" back in "the day"
Radios ....? Anything that says "TAIWAN R.O.C" on the back.
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Re: Cobra 148 gtl DX same power on all modes
Thanks for the replycb4ever104 wrote: ↑10 Jun 2022, 07:20 What's the voltage on the collector of the driver/final on SSB ? You should have about 5V on AM/FM and 13.8 on SSB .
About 5.5V on both AM and FM so guess that's the reason for the AM/FM level power output on SSB, just not sure why and I don't think I've had it before where AM power control affects SSB before.
Cheers
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Re: Cobra 148 gtl DX same power on all modes
whoops, I just measured again, properly.
5.5V AM, 9V SSB. Still not full voltage though....
Cheers
Nick
5.5V AM, 9V SSB. Still not full voltage though....
Cheers
Nick
- cb4ever104
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Re: Cobra 148 gtl DX same power on all modes
You should be getting the full 13.8V on SSB on the collectors . I presume it's a mk 2 ? If so , then check TR52 first , to make sure that it's switching as it should , and then TR51 . There isn't really much more to that circuit .
30TM060
Paul aka "Sammy". (108) PY60 Old Paisley DX Group (RIP Rab Markie)
Ex GM0 , now EA5 .
Handle "Fortune Hunter" back in "the day"
Radios ....? Anything that says "TAIWAN R.O.C" on the back.
Paul aka "Sammy". (108) PY60 Old Paisley DX Group (RIP Rab Markie)
Ex GM0 , now EA5 .
Handle "Fortune Hunter" back in "the day"
Radios ....? Anything that says "TAIWAN R.O.C" on the back.
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Re: Cobra 148 gtl DX same power on all modes
Thanks Sammy,
Will check in the morning and post back.
Cheers
Nick
Will check in the morning and post back.
Cheers
Nick
- ch25
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Re: Cobra 148 gtl DX same power on all modes
Wrong. It should be PS voltage minus V drop (0.7V) on C-E junction.
I bet there is a drop on fuse and lousy DC connector too.
Chris
WE ARE MOTÖRHEAD, AND WE PLAY ROCK N' ROLL
You can't have too many antennas...
You can't have too many antennas...
- cb4ever104
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Re: Cobra 148 gtl DX same power on all modes
My calculations were made assuming that his PSU was outputting 14.5V , so my statement is correct.
30TM060
Paul aka "Sammy". (108) PY60 Old Paisley DX Group (RIP Rab Markie)
Ex GM0 , now EA5 .
Handle "Fortune Hunter" back in "the day"
Radios ....? Anything that says "TAIWAN R.O.C" on the back.
Paul aka "Sammy". (108) PY60 Old Paisley DX Group (RIP Rab Markie)
Ex GM0 , now EA5 .
Handle "Fortune Hunter" back in "the day"
Radios ....? Anything that says "TAIWAN R.O.C" on the back.
- ch25
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- Call Sign: Lemmy
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Re: Cobra 148 gtl DX same power on all modes
WE ARE MOTÖRHEAD, AND WE PLAY ROCK N' ROLL
You can't have too many antennas...
You can't have too many antennas...
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Re: Cobra 148 gtl DX same power on all modes
Thanks guys. All sorted.
someone had stuck a different transistor in TR52 and it was dead. Replaced and putting out what it should.
Cheers!
someone had stuck a different transistor in TR52 and it was dead. Replaced and putting out what it should.
Cheers!
- cb4ever104
- Legend
- Posts: 6561
- Joined: 28 Jul 2011, 21:26
- Location: España
Re: Cobra 148 gtl DX same power on all modes
30TM060
Paul aka "Sammy". (108) PY60 Old Paisley DX Group (RIP Rab Markie)
Ex GM0 , now EA5 .
Handle "Fortune Hunter" back in "the day"
Radios ....? Anything that says "TAIWAN R.O.C" on the back.
Paul aka "Sammy". (108) PY60 Old Paisley DX Group (RIP Rab Markie)
Ex GM0 , now EA5 .
Handle "Fortune Hunter" back in "the day"
Radios ....? Anything that says "TAIWAN R.O.C" on the back.