Cobra 139 eBay score

[BBB]

Hi all. Just wanted to let you see my latest eBay score, a Cobra 139 AM/SSB base radio that I got for $19.

It had about an 1/8" of dust on it. That really doesn't discourage me from bidding because I'm thinking maybe it was retired on the shelf when the 40 channel radios came out and it's just waiting to be re-energized.

Sure 'nuff it powered right up and with a little switch cleaning was up and running on CRR. Unit was unmolested with the wax still in the slugs and the modulation still at the factory setting. It did swing a little better after turning the modulation pot VR12 up. AM dead keys at 4.5 watts and swings up to 10 watts. Does 16 watts on SSB.

A winning CB lottery ticket!

[cbrown]

Congratulations, looks nice!

[BBB]

Thanks. I really like it. It has great receive, decent modulation and the clarifier is open from the factory.

Just a simple, comfortable radio to use. I just saw another one go on the bay for $20, so they're out there and cheap still.

I'm wondering if I can lower the dead key from 4.5 watts to say 2-3 watts and still have it swing up to 10 watts.

[Sandbagger]

May 29, 2013 11:05:15 GMT -5 BBB said:

Thanks. I really like it. It has great receive, decent modulation and the clarifier is open from the factory.

Just a simple, comfortable radio to use. I just saw another one go on the bay for $20, so they're out there and cheap still.

I'm wondering if I can lower the dead key from 4.5 watts to say 2-3 watts and still have it swing up to 10 watts.

There is a 5 watt resistor marked "R148" on the board, which runs anywhere from 4.5 to 6 ohms depending on model. If you raise that resistor value to about 10 ohms, you will drop dead key down. There is already a capacitor in parallel with the resistor, and that should allow your peak power to remain which will give you more "swing".

[BBB]

We'll give that a try while the lid is still loose. Thank you. When I first get a "new to me" radio, I like to run them that way sometimes to see if anything is getting too hot.

I'd like the radio to have a little more Swangg if I can get that dead key a little lower. It's about a 1:2 ratio now. 1:4 would be nice ;D

[gator7]

Nice find, good luck with it.

73

[BBB]

Would that R148 be the one circled below that is already conveniently raised off the board like they knew we were coming?? That ones not ID'd on the board that I could see.





Thanks for the info.

[Sandbagger]

Jun 4, 2013 21:30:12 GMT -5 BBB said:

Would that R148 be the one circled below that is already conveniently raised off the board like they knew we were coming?? That ones not ID'd on the board that I could see.





Thanks for the info.

No, that's not it. The one you want is a 5 watt white ceramic rectangular block power resistor. There should be only one or two of those in the whole radio. It may not be mounted directly to the PC board, and may be simply attached to the mode switch, or mounted under the board.

[TRIPPLE NICKEL]

What a great find. Haven't been on in sometime, sure good to get back on and see something like this.
tripple nickel

[BBB]

Okay. Found it underneath as you suggested. 12 ohms gave a 1.5 watt DK, 8 ohms gave a 3 watt DK. I'll look some more for a 10 ohm that might yield a nice 2 watt DK. Still swings up to 8 watts.



I added a warm white LED lighting strip over the two gauges and channel selector. D/F tape and 12 VDC make installation a snap.





Just lay it in there until you get the desired results outside, then stick it. The LEDs face out the side of the "tape"



Now bright without the normal LED blue hue. These strips are scissor trimmable to 3 LEDs or about three inches long.

[Sandbagger]

Jun 5, 2013 13:00:41 GMT -5 BBB said:

Okay. Found it underneath as you suggested. 12 ohms gave a 1.5 watt DK, 8 ohms gave a 3 watt DK. I'll look some more for a 10 ohm that might yield a nice 2 watt DK. Still swings up to 8 watts.

I figured 10 ohms would be about right based on quick calculations. And I wouldn't rely on an unpowered wattmeter to give you an accurate peak swing value. They tend to show a bit lower than the actual value. For example, a true 4 watt dead key, 16watt peak swing @ 100% modulation would only show about 10-12 watts of peak on the unpowered peak reading wattmeter. I would use a scope to see the true peak value. Doubling the voltage on the scope is equal to 4 times the power (4X4=16). Also consider that many of those older 23 channel radios didn't have enough audio power to fully modulate a full 4 watt carrier (They were designed around a 3 watt carrier rating).

Those tape strip LED's are way cool. An easy way to shed some light on a dark radio meter(s).

[doctor]

A great find, I use to have one and sold it, wish I still had it, worked for years...
DOCTOR/795