8 & 9 Volt Regulators; best quality?

[Robb]

I have an <ughhh> Cobra 148 GTL NW/ST that refuses to allow the ALC to be be turned up. It becomes unstable on SSB. No surprise there - eh? Would putting in a better quality 9 volt voltage regulator help this radio out?

Or are there other known mods necessary - to turn this dog into a usable radio?


In addition, who makes the better quality/'brand' 8 volt regulators?

 

[unit_399]

In addition, who makes the better quality/'brand' 8 volt regulators?

I think your best bet would be a regulator from National Semiconductor or Fairchild. (LM7808 - 1.5A output). When you install it, be generous with the heatsink compound, and use a mica insulator instead of the thick plastic/ceramic thing that comes stock in the radio. Hope it fixes your problem. 73s.

- 399

 

[loosecannon]

i second what 399 said, i just want to add that i like to use a couple of 10uF caps on the legs of the 7808 regulators for some added filtering.

these regulators are very simple and straightforward to use.

looking at the face of the transistor with the legs pointing down, the left leg is the input voltage, the middle leg is ground, and the right leg is the 8 volt output.

first, add a 10uF electrolytic cap to the input and ground legs of the transistor with the positive of the cap to the input and the negative to the ground leg.

then do the same with the 8 volt output leg. add a 10uF cap with positive to the 8 volt leg, and negative to the ground leg.

run a wire from the switched side of the on/off switch (dont solder the wire right to the back of the switch, thats tacky LOL, trace the wire back to the board and solder it there) to the input leg of the 7808.

run a wire from the middle (ground) leg to PC board ground near where the power enters the radio.

run your 8 volt wire to wherever you need it.


how many watts can you get out of it before the ALC starts becoming unstable? what exactly do you mean by unstable?

most of the time you will notice when turning up the ALC that you will hit a point where the power does not increase any further, and you should stop there and then back it off a very slight nudge.
just wondering if you're trying to turn it all the way up.
LC

 

[Robb]

how many watts can you get out of it before the ALC starts becoming unstable? what exactly do you mean by unstable?

most of the time you will notice when turning up the ALC that you will hit a point where the power does not increase any further, and you should stop there and then back it off a very slight nudge.
just wondering if you're trying to turn it all the way up.
LC

That 'warble' sound . . . Less than 12 watts . . .

 

[mrgumby]

found this on the web at peg legs site

NEW INFORMATION ON THE COBRA 148 NW ST.

Cobra has really shot themselves in the foot with this new radio, why you ask? I'm getting to that but first let me say that Cobra has been the industry leader in producing good quality CB radio's down through the years, there was the great line of Mobil "AM" radios such as the 25LTD, 29LTD. Their Sideband radios such as the 146, 148 gtl and 2000 were superb, they were stable and a radio you could be proud of.

The first thing that happened to Cobra was that Uniden wanted to raise the price on there PC boards, Cobra did not like this so they got some other company to make there boards cheeper! The first thing that happened was that they started using 1/6 Th. watt resistors throughout the whole radio, don't know how many radios failed in the field because of this, I had several myself that had a failure of several resistors that had previously been 1/2 watt. Of course this is all history, they fixed that problem.

Now we have this new radio, the 148 NW ST, It looks real pretty at night. I had a customer send me a 148 NW ST for peaking and tuning for better receive and transmit. So before doing anything else, I hooked it up to my antenna to get some radio checks, well, AM was OK, nothing to write hone about but clear and clean. Then I went to Sideband, now people say they can't "clarify" me in, What! So I tried some others on the band with the same results, can't clarify me! So I'm thinking maybe my oscillators are off frequency so I check them and find that they are a little off so I align them. This time is the same as the last, they can't clarify me!

So I really got concerned! After checking the oscilator frequencies I find that they change when I modulate! What the Hell! they are not supposed to change, they are supposed to be rock solid! I placed a volt meter on several test points and found that the voltage to the oscillators is changing with modulation! So I start looking for the reason for this and ran into the cause right away.

The new units don't have the MB3756 Voltage Regulator, They have decided to further cheapen the radio by doing away with it! and installed a 3 pin voltage regulator in its place with a series resistor on the 8 volt pin, on the input pin there is no voltage drop, on the output pin there is.

What this all boils down to is this, the radio is in my opinion now is somwhat "unstable" on sideband and I for one, would not own one!

To my knowledge it could be inproved with some additional filtering and RF bypassing.