| Author |
Message |
    
738
| | Posted on Sunday, July 27, 2003 - 10:38 am: | 
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Hello, I have been off the radio for about 12 years and I'm rustyJ I found a Cobra 142 and ordered it. I found some of my old notes from 1989 or so. I had a note written on the Sams 219 to replace TR9 with a 2SC2999 lower noise transistor and re-adjust L10, L9 I don't think I did it. Does anybody know of this mod? I always want the best RX I can get. I can't find much now on searches for this radio; to old I guess. Also I'm looking for sources for Expo kits and any additional modifications for this radio.
Thanks! |
307
| | Posted on Sunday, July 27, 2003 - 5:43 pm: |
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The RX mod you are referring to does help a slight bit but is not worth the time. The best thing to do is to place "2" germanium diodes in parallel on the cathode side of the AM detector to ground. This will limit all spikes to .3 V and will "quiet" the receiver. I find it works well in most all radios.
307 |
738
| | Posted on Sunday, July 27, 2003 - 10:11 pm: |
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Thanks for the info. every little bit helps! Can you clarify the detail for me a little, I'm great at working on PC boards but I'm not a radio Technician! According to the Block diagram D22 is the AM detector, so I would find 2 Germainum Diodes put them in parallel and solder them from ground to the Cathode side of D22 (R64 Junction?) and their banded (Anode?) side goes toward ground? Thanks for the help, I always want to do anything I can to upgrade my receiving!J |
307
| | Posted on Tuesday, July 29, 2003 - 8:03 am: |
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Clarification:
Put the 2 diodes back to back in parallel , in other words cathode to anode on the pair , It almost looks like a short. Then place one side of the 2 diodes to D22 cathode , the other side of the 2 diodes to board ground.
307 |
738
| | Posted on Tuesday, July 29, 2003 - 9:24 am: |
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Thank's! Now it makes sense to me, clips the spikes either way! Will do, and the transistor only takes a moment to pop One in and out, and nothing is more important than the RX!
73J |
307
| | Posted on Tuesday, July 29, 2003 - 12:40 pm: |
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You got it! anything above 3/10's gets clipped. The typical level for AM Detection is only 1/2 of that. All the rest is noise that you don't want.
307 |
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