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I got it done but now the problem I have is a squeal when I key up and talk. If I keep the mic gain all the way down than it dont squeal but if I turn it up at all it will squeal as soon as you try to talk. I took the talkback out and it still acts the same as the needle still jumps up and swings full.
I did all the swapping of parts and the first adjustment to 50ma but I don't have a scope to put it on to do the rest. Is there something I can adjust to lower the squeal point. I know a few of you have done this mod before sence its been around for years but ...
Help me figure this one out please. I kept the parts so I can put them back in and undo what I did but I just wanted this old 148 to do better than stock. Can you help.
PS, I'm using a M6B power mic so I'm going to try to wire me up a five pin stock mic and see if that helps. Besides that I'm about at my end on what to do next. Help!
I did all the swapping of parts and the first adjustment to 50ma but I don't have a scope to put it on to do the rest. Is there something I can adjust to lower the squeal point. I know a few of you have done this mod before sence its been around for years but ...
Help me figure this one out please. I kept the parts so I can put them back in and undo what I did but I just wanted this old 148 to do better than stock. Can you help.
PS, I'm using a M6B power mic so I'm going to try to wire me up a five pin stock mic and see if that helps. Besides that I'm about at my end on what to do next. Help!
Try changing R196 back to its original value, you may have to play a bit on the value of it. Going by memory here but I seem to remember having a similar issue, and this was the only way I got it working properly..
I will give it a try. Thanks for the help. I'll keep you posted as to how it all works out. I'm just jumping in with both feet here with my first mod on a radio. Maybe I bit off more than I should have. Maybe not.
are you sure the radio was in stock condition before you started the mod?
did you do anything else to the radio while you were in the process of doing this mod?
do you know for a fact that the radio worked with this mic without squealing before you started the mod?
look at the front right section of the PC board and look for TR24.
its hard to find the markings, but it should be intact.
if its not there, or has one leg cut or has a resistor in series with it, return it to stock condition by replacing this transistor with a 2SC945.
also, check closely with a magnifying glass on the solder side of the PC board for any solder blobs that might be shorting two points together.
make sure that on the parts you worked on, your soldering is good, and is not shorting anything to anything else.
make sure you didnt set the radio down on something metallic that might be shorting things together.
i like to replace TR41 with a 2N6487, or an NTE152 transistor as they have a higher current rating than the stock transistor.
when you mod the radio like this you run the risk of overworking this transistor.
if TR41 says 1419 on it, you should definitely replace it, as they were too weak to begin with.
good luck,
LC
did you do anything else to the radio while you were in the process of doing this mod?
do you know for a fact that the radio worked with this mic without squealing before you started the mod?
look at the front right section of the PC board and look for TR24.
its hard to find the markings, but it should be intact.
if its not there, or has one leg cut or has a resistor in series with it, return it to stock condition by replacing this transistor with a 2SC945.
also, check closely with a magnifying glass on the solder side of the PC board for any solder blobs that might be shorting two points together.
make sure that on the parts you worked on, your soldering is good, and is not shorting anything to anything else.
make sure you didnt set the radio down on something metallic that might be shorting things together.
i like to replace TR41 with a 2N6487, or an NTE152 transistor as they have a higher current rating than the stock transistor.
when you mod the radio like this you run the risk of overworking this transistor.
if TR41 says 1419 on it, you should definitely replace it, as they were too weak to begin with.
good luck,
LC
I found my problem. I started putting things back like they were sense I saved all the parts and kept them in order. Then I got down to just R131. I left it out and checked again and squeal.
I had a couple beers and thought about this. Then I gathered it all up and took it out to the car. Hooked it up and then I could run the mic gain up to half before I got the squeal. Being new to this stuff I was just hooked to an antenna sitting on my table. Not a Dummy Load, so my SWR was too high and was causing problems. I didn't put the mod back in, I just left it out. I might try this again after I get me a dummy load so I have less problems. Live and learn!
At least this is what I think happened. Thanks to you all for the responses. Loosecannon I will check out what you said and take a good look at TR41.
I had a couple beers and thought about this. Then I gathered it all up and took it out to the car. Hooked it up and then I could run the mic gain up to half before I got the squeal. Being new to this stuff I was just hooked to an antenna sitting on my table. Not a Dummy Load, so my SWR was too high and was causing problems. I didn't put the mod back in, I just left it out. I might try this again after I get me a dummy load so I have less problems. Live and learn!
At least this is what I think happened. Thanks to you all for the responses. Loosecannon I will check out what you said and take a good look at TR41.
yes, this could have been your problem.
a dummy load is a good thing to have for any of us hobbyists.
i have done this mod a few times and havent gotten a squeal, and i have used the M6B with it before.
let us know what you find when you do the mod again.
oh, and make sure you didnt put that electrolytic cap in backwards!
later,
LC
a dummy load is a good thing to have for any of us hobbyists.
i have done this mod a few times and havent gotten a squeal, and i have used the M6B with it before.
let us know what you find when you do the mod again.
oh, and make sure you didnt put that electrolytic cap in backwards!
later,
LC
good point about the cap but I did do some searching on the WWW to find out what side was the pos and the neg so I did get it in right. I'll let you know how it turns out but I will be buying the dummy load first. Thanks for all who helped with this.
Some how I got talk back all the sudden, I think this is what's making it modulate.. I look at it on the scope and I have pure square waves..but.. I had to change the am power trimmer broke, I had a sweet 5k trimmer subbed and tried 1k2..
I put in a larger resistor 3k3 and tried the carrier, I had it so low I think it was all neg!! Bc when I raise the carrier it starts looking closer.
This is a cobra v148gtl dx with the wide audio amp and front Mic. I 're-vamped the final section with monolithic caps and 1/4 watt resistors so the peaks wouldn't blow the wussy lil resistors. But now I got this talk back effect.. I did go over the board touching up poor soldering I might have made a mistake.
But before I go combing through I figured I check
I put in a larger resistor 3k3 and tried the carrier, I had it so low I think it was all neg!! Bc when I raise the carrier it starts looking closer.
This is a cobra v148gtl dx with the wide audio amp and front Mic. I 're-vamped the final section with monolithic caps and 1/4 watt resistors so the peaks wouldn't blow the wussy lil resistors. But now I got this talk back effect.. I did go over the board touching up poor soldering I might have made a mistake.
But before I go combing through I figured I check