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Post by Phantom309 on Feb 28, 2009 12:20:19 GMT -5
Hi folks, I want to run a tug 8 on my cobra 2000. Some one sometime before I owned it got into it with wire cutters and a screw driver. I want to check and make sure they didnt cut R 131 but I cant locate it for the life of me. Can anyone give me a good pointer where it is the the board. I figure the tug 8 will make it a good skip shooter once I get it back to the factory settings but Im too scared to do it when I know the modulation was tampered with. thanks
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Post by BionicChicken on Feb 28, 2009 16:23:36 GMT -5
Check and make sure that TR24 has not been cut or removed if you are returning it back to stock. I have used a D104 on a 2000 with TR24 removed BTW. You just can't turn the mike up over about 1/3 of the way.
R131 is a 10K resistor attached to the base of TR26 and tied through diode D64 to VR12 which is the modulation adjustment pot.
BC
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Post by Phantom309 on Feb 28, 2009 16:42:36 GMT -5
yea thanks for the reply, I found r131 and it wasnt touched but they did clip tr 24 I nned to put one back in. Hopefully That should do it. Thanks for the help Bionic chicken.
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Post by mark4 on Mar 14, 2009 9:23:00 GMT -5
You should not run that 2000 with TR24 clipped. Per Barkett.
Strains the power supply and has fried a few power supplies.
according to Greg. I run mine with R131 clipped.
The limiter circuit in that radio tends to clip to much with R131 in-tacked. It will also cause a thud noise on your first syllable when the clipping kicks in. That is why most people run them with R131 clipped.
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Post by Tombstone (R.I.P.) on Mar 15, 2009 6:38:39 GMT -5
That's good information. I need to check my 2000 and see what some previous owner did to it and make sure that the transistor isn't disabled. All I was told is that the modulation has been"opened up'. I've replaced a few caps in the radio as they failed but never payed any attention to the modulation. Something's been done because the rig will overmodulate if I turn the mic gain up past 12:00, that's with the D-104 Silver Eagle barely cracked on. I don't notice the panel lamps dimming under modulation so I don't think it's straining the power supply but I need to make sure because I know that the supplys in these radios are a little weak to begin with. Wouldn't clipping the diode defeat the limiter too? I'll put the thing back to factory and see if I get the thud and if it happens then I'll clip the resistor, maybe that's what was done anyway. I just don't like to clip unless absolutely needed.
Tombstone
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Post by mark4 on Mar 15, 2009 10:33:53 GMT -5
If your talking about the diode in the right rear corner.
I would have to look up the #. It is a diode in the 148GTL model and a resistor in the 2000GTL. Pain in the butt to find the value. It was obscure on the schematic on line. But a friend had the entire printed service manual. Really makes no difference. Leave it in-tacked and clip R131. When R131 is clipped that circuit is disabled anyway. Make sure TR24 is not clipped.
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Post by Tombstone (R.I.P.) on Mar 15, 2009 11:29:07 GMT -5
Thanks, Mark 4!
Tombstone
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Post by Tombstone (R.I.P.) on Mar 18, 2009 3:23:17 GMT -5
Ha! mark4, right now I have my 2000 on the bench and after inspection I found that TR24 had been removed. I have a pile of those transistors and have it sitting into the board and am heating the soldering iron up and will remove the bottom cover of the radio and solder the transistor in. (hope it's good, I see no solder on the legs of the transistor but it still might be used, I just grabbed one) I'm in need of your expertise though, I can't locate R131, I found every resistor number except that one. Can you tell me the location? I need to see if it's been clipped or not. If it's still intact I'll run the radio and find out if I get that thud on my first syllable of a transmission, if it happens, then I'll clip. I see that the modulation pot is wide open and with a stock mic the rig is dead keying four watts swinging to about 15. I haven't changed the mic gain from the 12:00 position and haven't run it with the Silver Eagle mic yet but I don' plan on changing the mic setting from just barely turned up. A general location on the resistor will be appreciated and if the resistor is still connected I probably should leave the VR modulation pot open all the way unless you have suggestions on that. I know if the resistor is clipped that I'll not need to worry about that potentiometer. thanks much! I need to look very close at this rig and see if there are other genius modifications, ha, ha.
Tombstone
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Sandbagger
Administrator/The Boss 
Posts: 6,247 
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Post by Sandbagger on Mar 18, 2009 7:41:55 GMT -5
Ha! mark4, right now I have my 2000 on the bench and after inspection I found that TR24 had been removed. I have a pile of those transistors and have it sitting into the board and am heating the soldering iron up and will remove the bottom cover of the radio and solder the transistor in. (hope it's good, I see no solder on the legs of the transistor but it still might be used, I just grabbed one) I'm in need of your expertise though, I can't locate R131, I found every resistor number except that one. Can you tell me the location? I need to see if it's been clipped or not. If it's still intact I'll run the radio and find out if I get that thud on my first syllable of a transmission, if it happens, then I'll clip. I see that the modulation pot is wide open and with a stock mic the rig is dead keying four watts swinging to about 15. I haven't changed the mic gain from the 12:00 position and haven't run it with the Silver Eagle mic yet but I don' plan on changing the mic setting from just barely turned up. A general location on the resistor will be appreciated and if the resistor is still connected I probably should leave the VR modulation pot open all the way unless you have suggestions on that. I know if the resistor is clipped that I'll not need to worry about that potentiometer. thanks much! I need to look very close at this rig and see if there are other genius modifications, ha, ha. Tombstone IMHO, I've learned over the years that it's not a good idea to completely disable the AMC circuit. Splatter, distortion, and strain to the audio amp IC are a few of the undesirable side effects. TR24 is the main "shunt gate" which regulates the input audio. It is fed by both the ALC (SSB) and the AMC (AM). removing TR24 defeats both the AMC and ALC, which can lead to warble and non-linearity distortion on SSB. The alternative method, removal of R131, allows the ALC to continue to function, however, R131 is part of the bias network for TR26, which feeds AM audio back to the AMC circuit. Removing R131 will render the AMC inoperative as well. I would recommend leaving the circuit intact and adjusting VR12 for 100% or slightly more (but not allowing peaks to flat top). This way you'll still have high average modulation, but you won't have the harsh sound that occurs when peaks overmodulate, as well as the resultant splatter. If, for some reason, VR12 will not give you enough adustment range to reach your desired level, you can increase the value of R131 from 10K until the desired modulation is reached. But I wouldn't clip it out completely. As for the audio "thud", No radio did that more than the TRC-458 and other upd858 PLL radios, with all of the audio AGC circuits that they had. I've found that this is especially prevelent when using D104 mic's. When I use a Turner mic, the problem goes away. I suspect that the D104 sends a momentary "pulse" of audio when it's first keyed, which slams the AMC circuit resulting in the "thud" sound. You can probably minimize this by running the mic gain at a reduced level, and running the mic level higher to compensate. |
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Post by Tombstone (R.I.P.) on Mar 18, 2009 10:55:25 GMT -5
Thanks for the tips, Sandbagger, I replaced Tr24 and just need to locate R131 to see if it's been clipped. do you know the location of it on the board?
Tombstone
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Post by Marc on Mar 18, 2009 13:23:09 GMT -5
Tomestone
R131 should be right next to TR26 It is a 10K resistor.
Marc
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Post by Tombstone (R.I.P.) on Mar 18, 2009 15:05:49 GMT -5
Thanks for all of the help guys! I'll look again for R131, I looked last night using my mag lamp 'till my eyes started bulging. I just got off of the landline and talked to a reputable local tech. I told him aout the thud and he says that he's familiar with that but only with the "8" stands. he says it shouldn't happen with a "9" stand. Everyone seems to have a bit of a different opinion about this which is good because I'm in the experimental mode now. He also told me the location of the resistor and that correlates with what marc tells me so I'll look again now.
Tombstone
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Post by mark4 on Mar 18, 2009 16:03:49 GMT -5
As for TR24 that's why I recommended re-installing it.
Turner, that's fine if you want to run a Turner.
The best audio quality I have found is from a D104 in this radio.
If you clip R131 just keep the mic gain at a reasonable level.
You may also try a L Pad in your D104 and leave R131 in-tacked. This may resolve the thud on your first word.
I have not tried to increase the value of R131.
Sometime I will, to see if I get the desired result.
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Post by Tombstone (R.I.P.) on Mar 18, 2009 19:45:21 GMT -5
Well, it seems so far that my operation was a success, It would have been a lot more difficult without everyone's help. That goes to show why this board is rated number one. I located R131 easily with the guidance from all of you. It has not been clipped and I left it that way. Evideanally the Tr24 transistor that I put in after I found that someone had removed it is ok and working. Awhile back I made the tone control on the radio into a variable power adjustment and could get over six watts dead key with it turned all of the way up. Now I notice that I've lost between a watt and watt and a half depending on what frequency I'm tune to. I get 100% modulation with the mic gain on the radio set 3/4 of the way open and the Silver Eagle mic turned up about 1/4 Inch with clear rich modulation. It starts to echo and over modulate if I go higher with the radio's mic gain. Vr 12, the modulation pot was originally turned almost completely off, not wide open like I first thought so I turned it up fully and backed it down a hair. So far reports indicate that the radio sounds a good bit stronger with a better quality of modulation. I haven't checked out sideband but the test equipment shows tht it's working properly, I now just need to give the rig a work out and talk to people. As far as checking everything real close the radio is back to factory as far as I can tell except for the extra frequency kit and variable power. I've been running barefoot at an average of five watts and can turn down the dead key to about three watts when running my amp and may need to back the mic gain down some for that too but I haven't run the thing enough yet to tell. At five watts dead key it swings to 15 watts peak but I know that the readings are just relative. Nothing is clipped per modulation and no L pad modification was needed in the mic, nor am I getting any thud under modulation, just loud and clear so I'm a happy camper. As I run this radio now I may have to dress adjustments up here and there as I Talk to stations at various distances. While I was at it I replaced a burned out meter lamp too. Again, thanks for everyone's help!
Tombstone
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Post by mark4 on Mar 18, 2009 21:53:23 GMT -5
Glad you found it! I forgot to help you locate it.
I run mine with R131 clipped. I bought this radio last year and it is like NEW! except for the stupid shockty diode receive mod.
I replaced it to the original parts and re-aligned the entire radio back to factory specs. It works awesome. Another way to made this radio sound really bad is to put a swing kit in it. I am curious about the value change of R131. I am really picky about my audio.
About the only thing I talk on is my browning MarkIVA or Tram D201.
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Post by Marc on Mar 19, 2009 1:19:43 GMT -5
Glad to here all things came out ok.
that R131 change sounds interesting wonder if there is a resistor change like that for the 2950's hay Sandbagger is there a resistor change for the 2950 that you know of???
Marc
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Post by Tombstone (R.I.P.) on Mar 19, 2009 11:52:20 GMT -5
Yeah, mark4, I also found that when you're used to a Tram or Browning that anything else doesn't seem to cut it. The locals all say that my Brownings sound better than any of the other radios that I have. Unfortunately my Mark III and R27-S23 are off line awaiting the parts (funds) for 100,000 mile tune ups.
Tombstone
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Post by mark4 on Mar 19, 2009 15:32:54 GMT -5
You may have to play with the value.
I have done this before on a Realistic Navaho.
I know what Sandbagger is talking about. When this circuit is clipped out you have to be careful not to overdrive it. But you certainly don't want TR24 clipped. When I have time I will play with the value of R131 see if it gets me the audio I want.
Tombstone. I get wonderful audio reports. On my brownings.
I recently sold a MarkIVA to a guy that would not believe me that this radio would sound better with a browning 776 (Turner). Than his D104. I do run my MarkIVA from time to time with a D104 from time to time for a change. But not for long.
I sold him one. He called me yesterday and could not believe the difference! It was unanimous. Everyone told him don't go back to the D104.
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Post by Tombstone (R.I.P.) on Mar 19, 2009 17:36:55 GMT -5
I can beleive it about the 776 mic. The wonderful audio is always mentioned in the reports I get with my Brownings.
Tombstone
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Post by wd8nia on Mar 19, 2009 21:07:24 GMT -5
The 776 doesn't suit my voice characteristics on the Mark IV. My voice is so deep and raspy from nearly 50 years of cigarettes and nasty cigars I can't use anything but a D104 on any radio. The only exception has been the Astatic EchoMax 2000 I run with the 2990. In fact, I'd be very happy to trade my "custom" 776 with new cord wired for the MARK IV for a nice unamplified D104. Mic's on hold pending rig/mic deal/trade.  |
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Sandbagger
Administrator/The Boss
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Post by Sandbagger on Mar 19, 2009 21:20:54 GMT -5
You may have to play with the value. I have done this before on a Realistic Navaho. I know what Sandbagger is talking about. When this circuit is clipped out you have to be careful not to overdrive it. But you certainly don't want TR24 clipped. When I have time I will play with the value of R131 see if it gets me the audio I want. Tombstone. I get wonderful audio reports. On my brownings. I recently sold a MarkIVA to a guy that would not believe me that this radio would sound better with a browning 776 (Turner). Than his D104. I do run my MarkIVA from time to time with a D104 from time to time for a change. But not for long. I sold him one. He called me yesterday and could not believe the difference! It was unanimous. Everyone told him don't go back to the D104. The D104 has by far, the "brightest" audio tone quality, and the most punch and the perception of loudness. But there are other mics which can produc a more natural sound, albeit with less "booming" punch. The Turner +3 and Super Sidekick mate up well with most of my rigs, and in many cases sound better than the D104, if raw loudness is not the main objective. Certainly on SSB this is almost always the case. I've found that most CB ops tend to prefer that bright, hollow booming audio sound that a D104 tends to produce. This type of audio sounds loud and usually carries well in the distance and punches through the noise. But there are those of us who also like the flat natural tone broadcast quality sound as well. It's not as loud, but it works well for the local ragchews. I'm thinking the 776 mic is probably closer to this. I'd love to try one on my MK III. |
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Post by mark4 on Mar 21, 2009 10:19:16 GMT -5
I like clean Crystal clear audio!
Every radio sounds different because of it's audio circuit design.
One mic may sound good on one particular radio and sound like crap on another. I have heard a Super Sidekick sound fantastic on a friends President base on AM. And hear it on another radio that made it sound terrible. No fault of the mic. It's all about matching the right mic to the radio.
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Sandbagger
Administrator/The Boss
Posts: 6,247
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Post by Sandbagger on Mar 21, 2009 11:44:01 GMT -5
I like clean Crystal clear audio! Every radio sounds different because of it's audio circuit design. One mic may sound good on one particular radio and sound like crap on another. I have heard a Super Sidekick sound fantastic on a friends President base on AM. And hear it on another radio that made it sound terrible. No fault of the mic. It's all about matching the right mic to the radio. That's certainly the truth....... I've found that the SSK mates up well to the D201 (because of the tone control), and my Midland 13-885 (which tends toward a more "tinny" sound). It also does well on SSB. My Hy-Gain 623 is not so good of a match to the SSK, because it tends to emphasize the low end already. |
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Post by mark4 on May 4, 2009 8:51:16 GMT -5
As for the 776. There are some elements that were not so hot also. Hit or miss.
I have one here for the Cobra 2000 D64 is not a diode at all in the base it is a resistor no D64 on the parts list. They changed it to a resistor. It is shown on a diagram as D64 (R130) anyone know the value of this resistor. I think they used a diode in the 148 and changed to a resistor in the 2000.
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Post by mark4 on May 4, 2009 12:49:36 GMT -5
You may have one of the 776 mics with a borderline element.
These things varied just like D104 elements. I monitor the audio and have gone through mine replaced the ones that did not meet my picky standards.
As for the cobra 2000 I re-installed R131 and upped the value, way up! And no first word thump! But it still has the desired effect of clipping the harsh peaks and the radio has full modulation. Glad I tried it. Thanks, Sandbagger.
And if you did not read the previous post. Still looking for the value of D64-(R130) by VR12 was changed to a resistor in the 2000. D64 not on the parts list and no value listed for R130
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Sandbagger
Administrator/The Boss
Posts: 6,247
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Post by Sandbagger on May 4, 2009 18:08:40 GMT -5
You may have one of the 776 mics with a borderline element. These things varied just like D104 elements. I monitor the audio and have gone through mine replaced the ones that did not meet my picky standards. As for the cobra 2000 I re-installed R131 and upped the value, way up! And no first word thump! But it still has the desired effect of clipping the harsh peaks and the radio has full modulation. Glad I tried it. Thanks, Sandbagger. And if you did not read the previous post. Still looking for the value of D64-(R130) by VR12 was changed to a resistor in the 2000. D64 not on the parts list and no value listed for R130 I pulled up the 2000 schematic from CBtricks and it still has D64 showing. I also pulled similar MB8719 chassis radios and those which have the adjustment (148, 2000, Uniden Grant XL) have the diode. On the old Uniden Grant, it shows an R130, at 1.5K but there is no adjustment pot. I would imagine you could find the value rather easily. Whatever value allows the pot to adjust to 100% +/- would probably work ok. |
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Post by mark4 on May 4, 2009 18:21:21 GMT -5
Thanks, Sanbagger.
I have the 2000 service manual. Shows D64 on the schematic as a 1S1588 crosses to a (1N4148) signal diode. On the pictorial it shows D64 (R130) but neither were on the parts list. Strange. I have the diode installed. One of the things I really like about this radio is the great NB it has! I have the crappiest power line noise at times.
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Sandbagger
Administrator/The Boss
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Post by Sandbagger on May 4, 2009 21:12:09 GMT -5
Thanks, Sanbagger. I have the 2000 service manual. Shows D64 on the schematic as a 1S1588 crosses to a (1N4148) signal diode. On the pictorial it shows D64 (R130) but neither were on the parts list. Strange. I have the diode installed. One of the things I rally like about this radio is the great NB it has! I have the crappiest power line noise at times. That particular chassis has one of the best noise blankers on any CB radio. The Uniden Grant, and the 148 also benefit from the same chassis design. The 146 chassis also has a darn good NB circuit. Now if only Icom would copy Uniden's noise blanker design.......  |
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Post by mark4 on May 4, 2009 22:45:36 GMT -5
How would you rate the TRC-451 NB?
Never had one so I can't say.
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Sandbagger
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Post by Sandbagger on May 5, 2009 6:21:00 GMT -5
How would you rate the TRC-451 NB? Never had one so I can't say. I have a TRC-451 (It's the radio I use for my streaming audio server) and it's identical to the Cobra 146, and the NB is excellent. Although, as with the blankers on the other radios, when you use them, they do bring in more splatter-type bleed over. So it's a trade off whether you want noise or bleed. |
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