148GTL capacitor?? Hack recovery

[MrExtreme]

I have a 1991 148GTL that I found a couple leaky electrolytic capaitors so I am going to change them all. Question is, is there any downside to using higher quality, lower tollerance, audio grade caps, will this cause the radio to act funny. I understand a full alignment will be required after all this work.

The audio output is garbled, power seems low for all the mods it has, tr24 is gone, r131 is cut, d44 is gone, d52 is gone, unknown extra channel mod, clarifier mods. I am planning to return it to stock so I can monitor my mods as i go along, so the radio is not as screwed up as it is now. I got an Associates in electronic engineering, 20 years ago so I am relearning a lot of stuff, any help is appreciated.

Thanks Lee

 

[KD2GOE]

You will be fine just use high quality caps Rubycon, Nichicon, united chemi con capacitors

I did my uniden washington with them use 16v or higher caps and high temp there is a few caps you can up the value in the power handling prts there is 2 1, 000 uf caps you can put 3, 300uf and so on some people can comment that are more knowledgable..

 

[9C1Driver]

With the older style 148's they don't need "all the mods" and should not be clipped. I would go back through it and try to get it back to stock, then give it a correct tune/alignment. Expect 14-18 peak watts that sound super smooth and clean. It will never be a 30+ watt radio nor should it have to be to sound good.

 

[Robb]

I would restore it all to stock too, except for the clarifier mod. I would let it slide no more that it would do stock, as this is easier to control. Replace all of the electrolytic caps is a smart idea. The older radios seem to need them, as I have gone through this situation fixing oldies and found too many bad caps and went ahead and replaced them all. It is tedious; but still the right move - IMO.

There is no problem using higher grade caps. The ones that come in radios are just fair. Not really going to notice any difference. If you want better audio quality/wider range, there is a mod for that.

 

[KD2GOE]

x3 on the stock I am working on my 3ed radio returning it to stock... I talk side band with people and you need a clean radio or they cry

 

[MrExtreme]

Thanks for the confirmation. Looking at Justin's mod, after I get it back closer to stock, replace components etc.

Just looking for the "awesome" audio, not needing much for power mods as I have a TS350 to go with it.

I saw a page where a guy suggested replacing the 1588 diodes with 4148s, also if replacing the diodes 1N60 in the receive and NB works, what about replacing the other 1n60s with the same diode 6263?

I also am replacing the 1614 transistor with the 2999, would replacing all the other 1614s with 2999s be a good or bad thing?

Thanks Lee

 

[Robb]

The 2sc1674 change to a 2sc2999e I would not recommend. Mixed results; usually not favorable. Changing the four 1N60 in the receive and noise blanket diodes to 1N6263 is always a solid move and is recommended.

Awesome audio is what you want?

"Goldfinger's Cobra 148/2000/Grant XL audio mod"

TX

C46 Change to 2.2uf mylar/polyester film or non-polarized electrolytic
C101 Change to 1.5uf tantalum 16 to 50 volt
C102 Change to a 910pf ceramic disc
C104 Change to 2.2uf tantalum 16 to 50 volt
C108 Change to 1uf to 2.2 uf tantalum 16 to 50 volt
I found that if you have a very deep voice start with 1uf on C108
and work up if need be.
If you need more highs on tx Change C 105 to .001 to .0001uf mylar/polyester film The smaller you go the more highs you get.

RX

C71 Change to 1uf mylar/polyester film or non-polarized electrolytic
C75 Change to .001 to .0001uf this will give you more highs on rx
optional
C76 Change to 2.2uf mylar/polyester film or non-polarized electrolytic
C182 Change to .001 to .0001 for more highs on rx and tx
optional
C183 Change to 2.2uf mylar/polyester film or non-polarized electrolytic
C187 Change to 2.2uf mylar/polyester film or non-polarized electrolytic
With C75 and C182 you can start with no Change to them, then if you feel you want more highs then change them out

 

[MrExtreme]

Thanks Robb, btw what do you think of this mod, will it work along with what you posted? Thanks Lee


1. Carrier Adjustment: VR10. If lower carrier is desired, change R196 near VR-10. Try about 270 ohms.
2. Change R114 to a 10K, and C46 to a .2 monolithic, this will widen up the audio on AM.
3. The AMC is TR-26. You can remove it, and still have good results on AM, the ALC for SSB is not effected by this. If you don't want the AMC disabled, leave it. the other way to disable the AMC is cut R131. Check both to restore AMC from previous mods.

4. If extra frequencies have been added, perform the following to widen up the band pass filters to recover lost power at the highest and lowest frequencies: C163 - 4pf, C41 - 3pf

5. R180 - Jumper it. This brings up the gain of the TX mixer.

6. IC TDA6130 - Pin 12 to ground through 100 ohm resistor. Upper left, pin 14 = ground.

7. Remove the AM regulator, (usually a 2SC1419) and replace it with a 2N6487.

8. C174 - remove, add 1000uf electrolytic. connect POS to base of yellow wire next to it. If the yellow wire is too far away, it might be easier to connect the POS leg to the leg of the AM regulator closes to the back of the chassis via the bottom of the radio.

9. For 148F, change C18 to a 1000uf electrolytic, 16V

The 2sc1674 change to a 2sc2999e I would not recommend. Mixed results; usually not favorable. Changing the four 1N60 in the receive and noise blanket diodes to 1N6263 is always a solid move and is recommended.

Awesome audio is what you want?

"Goldfinger's Cobra 148/2000/Grant XL audio mod"

TX

C46 Change to 2.2uf mylar/polyester film or non-polarized electrolytic
C101 Change to 1.5uf tantalum 16 to 50 volt
C102 Change to a 910pf ceramic disc
C104 Change to 2.2uf tantalum 16 to 50 volt
C108 Change to 1uf to 2.2 uf tantalum 16 to 50 volt
I found that if you have a very deep voice start with 1uf on C108
and work up if need be.
If you need more highs on tx Change C 105 to .001 to .0001uf mylar/polyester film The smaller you go the more highs you get.

RX

C71 Change to 1uf mylar/polyester film or non-polarized electrolytic
C75 Change to .001 to .0001uf this will give you more highs on rx
optional
C76 Change to 2.2uf mylar/polyester film or non-polarized electrolytic
C182 Change to .001 to .0001 for more highs on rx and tx
optional
C183 Change to 2.2uf mylar/polyester film or non-polarized electrolytic
C187 Change to 2.2uf mylar/polyester film or non-polarized electrolytic
With C75 and C182 you can start with no Change to them, then if you feel you want more highs then change them out

 

[Robb]

Well, I've seen those mods that you've listed before. I have not tried them myself. I have tried the mods I did post and they work quite well.

The difference, is that the mod list I put up are all cap mods which directly affect the audio bandwidth in TX and RX. They do not affect audio output strength, just allow all the audio that the circuits already have before they pass through the xtal filter, which will ultimately limit the audio bandwidth. One does not need to boost the audio, since the radio has enough already anyway. What it does is to allow the best compromise of hifi audio without changing the xtal filter out.

7. Remove the AM regulator, (usually a 2SC1419) and replace it with a 2N6487.

This can be substituted with a NTE-152 as well, which in this case is the better part. It is an upgrade for the 2sc1419 that has been known to fail often. It doesn't do much for audio, other than make sure it doesn't snap because the NTE part has better specs.

3. The AMC is TR-26. You can remove it, and still have good results on AM, the ALC for SSB is not effected by this. If you don't want the AMC disabled, leave it. the other way to disable the AMC is cut R131. Check both to restore AMC from previous mods.

Nope; I wouldn't do it! But I would check both parts TR-26 and R131 and replace them both if they have been removed. If cut; then just solder them back together. 'Loud' isn't better if it causes the audio to get into distortion - which it will if these mods are done. Clean, wider audio is easier to understand than loud, distorted audio.