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New channel LED install
- Thread starter Robb
- Start date
I was actually kidding, Robb. 
If you really want to know for experimentation/test purposes, you change R228 to a 1.2k ohm resistor, and then install a 1uf, non-polarized capacitor between pin 9 of the audio IC and the junction of R228/D63/R194. Make sure that all mod limiters are intact and adjust the AMC for 90-95% on the negative peaks. That's all you need to do. 2-3W deadkey is optimal for this mod.
Let me know how it works for you.
~Cheers~
If you really want to know for experimentation/test purposes, you change R228 to a 1.2k ohm resistor, and then install a 1uf, non-polarized capacitor between pin 9 of the audio IC and the junction of R228/D63/R194. Make sure that all mod limiters are intact and adjust the AMC for 90-95% on the negative peaks. That's all you need to do. 2-3W deadkey is optimal for this mod.
Let me know how it works for you.
~Cheers~
Naw, wasn't going to do it to this radio. Just wanted to know what the final tally was. I'm certain that replacing the AM Regulator is also indicated since modding it that way would surely push it past its limits. Much appreciated.
It certainly wouldn't hurt to replace it, especially if it has the infamous 2SC1419 in it. I'd replace it with a 2SC1061 or a 2SD1135.
~Cheers~
~Cheers~
I have been using the tip-41c for a replacement now for about 3 years and they have worked good so far for me. running them in 4 of my personal radios and no failures as of yet. my buddy has been using them for 2 years at his repair shop and he has been in business for over 40 years now and he says they are working for him also. he is using the tip36c to replace the 2sb817 and no failures.
Older Cobra 148 GTL rebuild
Just thought I would update the channel LED install. Burned up one ch LED because it had too much voltage. So I replaced it again. This time I removed a jumper between the 5v regulator and the feed to the ch LED and installed a 10k/ohm VR control to bring down the brightness. I checked the resistance after I found a sweet spot; about 3.3k/ohms - YMMV.
Radio was a basket case purchased from a Hamfest for $20 that I used to learn repairs. Modified it too. 455khz wider filter for 6khz AM bandwidth. HiFi receive/transmit audio mods. Completely recapped. New ch switch; was most expensive part to replace ($18). New voltage regulator w/zener added as per bulletin #1226. Schottky diodes too. Completely aligned it as well - of course. New case screws; the old ones were rusty and nasty. Everything works like it should now. Didn't use a blue LED (tried it too) for S/RF meter because the white LED makes it easier to read than a blue one does - IMO. TX/RX light replaced with red/blue tx/rx. Much more . . .
Just thought I would update the channel LED install. Burned up one ch LED because it had too much voltage. So I replaced it again. This time I removed a jumper between the 5v regulator and the feed to the ch LED and installed a 10k/ohm VR control to bring down the brightness. I checked the resistance after I found a sweet spot; about 3.3k/ohms - YMMV.
Radio was a basket case purchased from a Hamfest for $20 that I used to learn repairs. Modified it too. 455khz wider filter for 6khz AM bandwidth. HiFi receive/transmit audio mods. Completely recapped. New ch switch; was most expensive part to replace ($18). New voltage regulator w/zener added as per bulletin #1226. Schottky diodes too. Completely aligned it as well - of course. New case screws; the old ones were rusty and nasty. Everything works like it should now. Didn't use a blue LED (tried it too) for S/RF meter because the white LED makes it easier to read than a blue one does - IMO. TX/RX light replaced with red/blue tx/rx. Much more . . .
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6khz wide Murata 455khz 2nd IF filter: CFWLA455KFFA found at Mouser.com
About $2-3/ea.
Not really, have been using it the last couple of days. Try one and then change it back out if it doesn't work out for you. The SINAD program I use has a real-time audio analyzer and I can see that it does have 6k - verifiable.
I have it installed in my 148 and there was a noticeable Increase in bleedover
but nothing I'm not used too, I think its a very good trade off, a bit more bleedover but an noticeable increase in rx freq. response. It sure makes a difference when a wide station comes rolling in...... just my 2 cents
but nothing I'm not used too, I think its a very good trade off, a bit more bleedover but an noticeable increase in rx freq. response. It sure makes a difference when a wide station comes rolling in...... just my 2 cents