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gasman
06-28-2014, 06:44 PM
Can anyone tell me which is the modulation pot on a 1997 cobra 25ltd classic? I have awfully low audio output on this radio and am trying to figure out why.

222DBFL
06-29-2014, 02:16 AM
VR5. That should be the modulation pot

gasman
06-29-2014, 09:13 AM
That's what I thought 222. I opened up the radio, found it turned all the way to the right. I turned it all the way to the left and it only got worse. this radio was peaked and tuned when it was new. I have very low modulation even running it with a palomar 225. Do you or anyone else have any ideas what I can do to rectify this? Thanks for the info 222.

222DBFL
06-29-2014, 09:38 AM
Not without the proper test equipment. I know it's not what you want to hear, but without a good meter to measure the modulation, then you are just guessing. If you want to run and amp you have to suppress the am carrier, you can do tins with the cap and resistor mod or the TIP120 mod. The resistor cap mod is the easiest way, keep your dead key at at around 1.5-2 watts max. But you need to have a way to do all of this, an oscilloscope or at least a good watt meter and dummy load, a watt meter that can measure modulation.

gasman
06-29-2014, 11:38 AM
O.k. 222 any recommendations on what type of meter or o scope I should look into? My backround is in appliance repair so I am well versed in reading diagrams and using a multi-meter. I imagine this will be along those same lines. I have an astatic pdc2 swr/power meter, however I get the feeling this will not accomplish what I will be attempting to do. Thanks for your input and any recommendations.

BOOTY MONSTER
06-29-2014, 12:34 PM
sell it and get a older side mic cobra or uniden .

gasman
06-29-2014, 01:59 PM
This is an older side mic cobra. 1997. Do I need to go older than that? I bought this radio new. I used it for a number of years. then I stored it in the original box for close to ten years before I dragged it out and set it up in my p/u. Running it with a roof mounted Wilson 1000. Apparently the palomar 225 isn"t helping it any. I was talking to a local who is maybe a mile away and he said he could barely hear me.

222DBFL
06-29-2014, 02:09 PM
That amp doesn't like a dead key above 2 watts. I have one, it's has 2 sd1446's in it, a uniden 980 works well with it. They don't like to be over driven, and if your radio has had the golden screwdriver in it, it's going to make the issue worse. Also, check all your connectors, jumpers and antenna coax as well. If you have a newer wilson 1000 with the 2 piece connector on it, that would be the first thing I would replace, then I would check all my connectors on my coax jumper from the radio to the amp. And last, have you checked the swr reading with the amp out of line to tune the antenna properly? Like said before, you need a good meter that can set modulation to 100% maybe a bit less, an oscilloscope would be best. Idk which one to tell you to get, but would think one that measures to 1-100mhz would work. Check eBay out, there are a bunch out there!!

gasman
06-29-2014, 04:01 PM
Thanks again 222. Right now the amp is out of the circuit. Swr is 1.3-1.7. According to the radio meter deadkey is 1w with the mic gain turned up. It's not even swinging to 2w. The antenna coax does have the two piece connector, however there is no issue with my connex 3300 on the same setup. (minus the amp)

gasman
06-29-2014, 04:03 PM
also, don't know if it matters but I am running a ranger noise reducing mic on the cobra.

222DBFL
06-30-2014, 03:27 AM
Your swr readings are a little high for an amp to be run, should be 1.3 max. Something is wrong with the radio if it keys 1 watt and only swings to 2 watts. And the connector issue may not show with no amp, less power. It's when you add power that these connectors go bad, been there done that. Get your swr reading as low as possible, it may be the radio like said above. If it's been tweaked by a golden screwdriver then who knows what the issue could be , can you post some photos of the inside of the radio as this may help with trouble shooing the issue. There are some very knowledgable guys here, but we need all the info you can give, photos of the inside of radio and a photo of the amp as well. Again, check all your coax jumper connections with an ohm meter to make sure that none are shorting. And check around on eBay, might find a good scope to use or even a good watt meter that has modulation setting, and not a dosy meter either!! If you are serious about the hobby, then spend the money and get the right equipment, I am in the same boat as you, I am now in the process of gathering the proper equipment to test my radios and make sure they are working correctly. The radio you have can be had for relativity cheap on eBay or Craigslist. Just have to look around. May be your cheapest soliton like booty monster has stated. I have picked those radios up for 15-30 dollars. Find an old side mic one and you will have a good one. Personally I would look into a uniden 980 for that amp, it's not a power house, but will push that amp just fine, to turn the dead key down on the 980 you can simply turn the power down some. Like I said it's not a power house, but has clean audio. Also I have the same type amp and it doesn't like much over 15 watts pep. It gets hot and starts to pinch the audio as well. That amp shouldn't need much to push it. Again these are all JMO. But I would look around for a good used one that hasn't been molested!! God bless.

gasman
07-10-2014, 03:37 PM
Ok. So I have purchased a better meter than what I already have. I am going to spend some time Saturday trying to work out the kinks. Am still looking at replacements for the cobra. Will ask for more info after adjusting s.w.r. On Saturday.

222DBFL
07-11-2014, 02:09 AM
Replacement radio? What you looking for? am only or am and ssb. Have a couple of radios that are AM, cobra 25, and an old galaxy dx55. Both are unmolested. Just been tuned and aligned. No whack pack BS!! Might be interested in selling. Don't have to, but will to help another member.

gasman
07-11-2014, 07:17 AM
We'll I am going to be honest and embarrass myself. Recently (before I found this forum) I traded in my galaxy dx959 for a swp II connex 3300hp. (Oh the shame!!!). Luckily enough this connex seems to be working just fine. A little disappointed in its performance, thought it would get out a bit farther. Fm is a waste. 240 channels only use maybe a dozen channels on a.m. I am going to my first hamfest this weekend and I am going to look around. I did some research on the bearcat you mentioned earlier on in this thread, it's a nice radio but I'm not sure how I feel about the digital display. I like the old school analog meters. I plan on keeping the cobra 25 and attempting to "fix" it. What year is the 25 you have? Is the mic a front or side mount? Thanks again 222 for all of your help.

222DBFL
07-11-2014, 09:46 AM
It's an older one, pre china, can't dement if it's a side mic but I believe it's front mic. It has been tuned and aligned by a good tech with an oscilloscope and good meters. No limiters clipped. It deka have the carrier suppression installed and has a 2 watt dead key. I just don't use any of my AM only radios anymore. I also have a nice 29 lx le that had the final replaced with a 1969 final, but it has a stupid echo board installed. Still works well though. And last, my old galaxy 55 dx. Great AM radio. Good audio and no clipped limiters. Just tuned and aligned. Don't like having my radios hacked on!! My next radio is going to be a real one. Looking at the icom ic-7200. Next month is my bday!! Can't wait lol. I am a big kid!! Can't have enough radios! Anyway, god bless and have a great day.

gasman
07-11-2014, 05:11 PM
I just had a look at that Icom. It's a really nice radio. I have ALOT of learning to do before I get into something like that. I am leaning toward something with at least am/ssb capability. Going to collect as much info as possible about ham radio at this ham fest on Sunday. Christmas is coming soon, haven't decided if I am gonna ask Santa for a BIG amp or an RCI 2995dx. Still have a little time to sort it out. Thanks again 222. Will post tomorrow results of my swr tune, see if maybe there is an issue with the mic on the cobra 25. Have a dumb question, I have an astatic power mic wired for an old 5 pin realistic radio, can I put a connector on it to fit the 4 pin cobra or does the mic need to be re-wired?

222DBFL
07-11-2014, 05:43 PM
Mic most likely needs to be re- wired for 4 pin cobra. And with it being a power mic is the power external or does the mic get power from the radio, that might be what the 5th pin is for, 8v for powering the mic. If it has it's own battery than yes it should work but will need to be wired for the 4 pin cobra style mic's.

gasman
07-11-2014, 07:19 PM
Mic itself holds a 9v battery. When you say re-wire,does that mean changing just the connector or replacing the cord as well?

222DBFL
07-11-2014, 07:48 PM
Just the connector.

222DBFL
07-11-2014, 07:50 PM
Need to find out which is tx. Rx, ground and shield. Check Cbtricks for the schematic for that mic. May show what or how to wire it for 4 pin cobra.

gasman
07-11-2014, 07:51 PM
Triple deuce you are a godsend! Thanks for your insight and more importantly your patience!!!

222DBFL
07-11-2014, 08:30 PM
No worries man, I will try to help as much as I can!! I am no expert, but do dabble a bit! I am stepping my game up as I go along. Next up, ICOM 7200 a real HF radio. Can't wait!! But anyway again no worries ask away! Have a great one and god bless.

gasman
07-12-2014, 02:37 PM
Ok. Checked swr. Ch 1 dead key is 1. Channel 20 also is at 1. Channel 40 is 1.1. This is with both the cobra and connex. I know it shouldn't change between radios and it didn't so that's good. Cobra mic gain was turned all the way up. With this new meter dead key is 2w swings to 6w on ch 1, 8w on ch 20 and 10w on ch 40. Is this normal? Connex with mic gain @ 1 o'clock is also 2w. Swings to 20w on ch 1, 25w on channel 20 and 30w on ch 40. Again, normal? Now for the 2 golden questions: 1. When speaking into the mic the swr needle swings, is this indicating the ref power? And 2. My Palomar 225, if I use my connex on this amp do I need to cut the power off in order to not burn it up? We'll start with this and maybe later we can get into why high voltage can't hear me on the cobra with the amp on at a stones throw away. Thanks.

222DBFL
07-12-2014, 05:55 PM
To properly check swr, turn mic gain all the way down, no modulation. Calibrate meter and take readings. Your dead key on the radio should be around 3-4 watts , mic gain all the way down. And don't worry about the needle moving while taking, that is normal, like I said, swr readings require that no modulation be used. Only a carrier. Your dead key should be above 2 watts, 3-4 watts dead key is normally what is needed. Check the specs on the meter you have. If possible look at the directions or google it and try to find some directions. Here is a page about checking swr as well. http://www.cbtricks.com/members/toban/swr.htm
And yes for that amp, you want the amp to have a 1:4 ratio carrier. So if the amps total output is 200 watts, you want the amp to have a carrier of 50 watts. These amps don't require much dead key, normally between 1-2 watts and pep of 12-15 watts is about max. I would keep using the cobra 25 with it and get your dead key down to 1-2 watts. This can be done with a cap and resistor mod or a TIP120 mod. Check out Cbtricks for more info as well. Good place to get info for the 2 radios you have. Hope this helps and god bless.

gasman
07-15-2014, 01:12 PM
Hello again. So I went to the Sussex ham fest and I purchased a Texas star 250hdv. I did a temp hook up to check it out. It powers up, pre amp works but I am not seeing any power increase on my meter on tx. The meter built into the amp does not move either. Did I do something wrong or did I get goonched? Is there any way I can check the 2 2289 finals with a multi meter and if so am I looking for dc voltage or ohms?

222DBFL
07-15-2014, 04:21 PM
You need an external swr/watt meter. Radio shack has a decent one for mobile use. And make sure the radio you are using has the am carrier set to 1-2 watts max. Do not stick a volt meter in that box, you can burn the transistors. They need to be taken out to be tested properly. But first if would get a watt meter and place it in line after the amp. So it will go, radio to amp, amp to watt meter, watt meter to antenna. And what radio are you using? What is the dead key set to? I would not run more than 2-3 watts dead key into that amp. You want the amp to key up at about 1/4 the total output. So a 250 watt amp would key up around 50-60 watts. Then let it swing from there. Use a single final radio as well and the amp will last a very long time. Over driving the amp will send it to the grave early. But anyway. Check all these things and if in doubt send the radio and amp to a good tech and have them match the radio and amp. This way it will definitely work properly. Have a great one and god bless.

gasman
07-15-2014, 04:58 PM
I used an astatic 600 swr/power/modulation meter hooked up as specified. Running my connex 3300hp with power turned all the way down its 2w d.k. This was how I checked the amp. I seemed to get nothing out of it. I will hook it up properly when it stops raining and try again.

222DBFL
07-15-2014, 05:10 PM
Does the amp have a variable knob or is it the button type. The variable knob is a weak point on those amps. How much you have in it? Might be worth it to send it off to a good tech.

gasman
07-15-2014, 05:43 PM
Yes it is a variable power amp. Bought it Sunday for $80. Any ideas how to tell if it's the v control? I'm pretty confident I could change that myself. The issue I have is trouble shooting the thing. I can read a diagram/schematic, can even find info on the part specifics. Just not sure where to start. If only I knew the sequence of operation and what parameters to check the specific components for.

gasman
07-15-2014, 05:52 PM
Is the variable power device like a potentiometer? Can I just jump it out to check it or will I fry everything? I know once you let the smoke out, no matter how hard you try, you're never able to put it back in.

222DBFL
07-15-2014, 07:41 PM
I am not sure. Try a google search and see what comes up. I know that the variable is a weak link though from other Posts on other forums. Open amp up and have a look it may be a heavy duty potentiometer. I have never had a variable power like that, only ones with switches. Maybe someone with a bit more knowledge will jump in and help out. Popping the lid and looking around will help. Also another thing to look for is burnt resistors next to the inputs for the transistors. Look for any burnt resistors. If they are burnt the transistors may be bad but for what you paid, you could rebuild it for way cheaper than a new one!!

gasman
07-15-2014, 08:04 PM
Thanks again 222! Wish you were up this way so I could buy you a cup of joe. You've been a great help. Will update progress as I make it. Gonna borrow a few books from a buddy who took electronics classes years ago. See where that gets me. For reference do you recommend any radio shops? Unfortunately around here there are none.

222DBFL
07-15-2014, 10:15 PM
No worries man, one day pass it forward. Help someone. That's all I ask. It's good karma!! Seriously, I wish I could help more, just not an amp expert. Not my forte'. But I have learned a few things through my own experiences and through reading posts. Hope you get it fixed and god bless.