Cobra 29 LTD Classic 50w?

[Hawkeye351]

Just got done with an old, old school Cobra 29 LTD Classic (sidemic). This radio is bone stock, other than the cap/resistor combo (470uf 25v + 56 ohm 1w) in place of JP36. This radio has the stock final and driver in it with no power/tweak mods at the final (R56, etc...). No parts are clipped or cut anywhere.

But yet, after the complete alignment, the radio is putting out 50w PEP exactly and it's clean on the spectrum and scope.

My question is HOW? I've looked over the schematic to compare the parts on the schematic to the parts that are in the radio, everything is stock.

How is a stock Cobra 29 Classic with a stock Cobra 29 final doing a clean 50w PEP? Most I've ever gotten was around 38w PEP.

 

[secret squirrel]

See if it is reproduceable results with another meter. Are you able to take the measurements with the scope. I openly admit a 12 y/o with a Radio Shack 200 and 1 Electronic Project Lab would be able to do a better solder job than me. Any successful experiment should be able to reproduce empirical results. Try another meter and or scope, that would be your most obvious variable.

 

[nomadradio]

How much carrier?

There was a 68pf disc cap that got added to the driver circuit to hot-rod this model, might be on the board's solder side.

Got me baffled.

73

 

[loosecannon]

im confused as to how the pattern looks clean on the scope with the swing mod installed?
LC

 

[Hawkeye351]

Not sure how it ended up with a clean signal. Only the fundamental frequency spike pops up when I key up on my spectrum. Normally I see a little bit of a second harmonic and a few little booger bumps on the analyzer with 29's/78's, etc...

The clean signal even with the cap/resistor combo has got me stumped, I normally see some distortion on the analyzer and scope, but not this one. HOW?

Without the cap/resistor, the radio would key 9w and swing around 40w, but after the cap/resistor combo I got the key down to a 4w deadkey but the swing increased by exactly 10w.

I also checked for that disc cap off the driver transistor, which I have seen in other 29's, but this one doesn't have it, it's all stock.

The owner got the radio back yesterday, he's shocked also. He hooked it up last night on his meter (dosey) at his house. I asked him to get back with me to tell me what he sees on his meter, so he did and said his dosey shows around 42w peak. I listened to him talk on it last night. He lives about 7 miles from me. I switched back and forth from the channel he was talking on to the next channel up and down from the channel he was on to check for splatter, almost non existent bleed over with him running his 4-tube elkin behind this 29. He was getting compliments on the clarity and loudness of his signal, even I was impressed. You'd think it would be choppy, splattering, distorted, etc....but no, it's a crystal clear but yet loud radio transmission.

I guess it's just one of those "Diamond in the Rough", once in a lifetime rigs.

Everyone around here tells me I'm the best tech they've had around here, but I'm not that damn good, lol...this radio just happened to turn out this way by luck.

 

[DelR]

Not sure how it ended up with a clean signal. Only the fundamental frequency spike pops up when I key up on my spectrum. Normally I see a little bit of a second harmonic and a few little booger bumps on the analyzer with 29's/78's, etc...

The clean signal even with the cap/resistor combo has got me stumped, I normally see some distortion on the analyzer and scope, but not this one. HOW?

Without the cap/resistor, the radio would key 9w and swing around 40w, but after the cap/resistor combo I got the key down to a 4w deadkey but the swing increased by exactly 10w.

I also checked for that disc cap off the driver transistor, which I have seen in other 29's, but this one doesn't have it, it's all stock.

The owner got the radio back yesterday, he's shocked also. He hooked it up last night on his meter (dosey) at his house. I asked him to get back with me to tell me what he sees on his meter, so he did and said his dosey shows around 42w peak. I listened to him talk on it last night. He lives about 7 miles from me. I switched back and forth from the channel he was talking on to the next channel up and down from the channel he was on to check for splatter, almost non existent bleed over with him running his 4-tube elkin behind this 29. He was getting compliments on the clarity and loudness of his signal, even I was impressed. You'd think it would be choppy, splattering, distorted, etc....but no, it's a crystal clear but yet loud radio transmission.

I guess it's just one of those "Diamond in the Rough", once in a lifetime rigs.

Everyone around here tells me I'm the best tech they've had around here, but I'm not that damn good, lol...this radio just happened to turn out this way by luck.

I got 2 old 29s, I want you to do that to...

 

[Wire Weasel]

Something is wrong

 

[Hawkeye351]

I got 2 old 29s, I want you to do that to...

I didn't do anything no different than I do to other 29s, this one just turned out this way. Lucked up...

 

[AudioShockwav]

That radio was originally a Wednesday morning build radio, the guy putting it together had a nice dinner the night before, and spent the evening with with his beautiful wife.
That next morning he felt great and had steak and eggs for breakfast before work.
On the way to work he stopped by the Union Station were he found a crisp $10 bill blowing across the lot that paid for his gas.
As he started his day, the supervisor came over to tell him that because of his exemplary work record he just got a 15 cent pay raise.
As he started work,
by accident he grabbed the highest gain transistors out of the parts bin that morning, and carefully built the first radio of the day with pride...

Some days you just get lucky.

73
Jeff

 

[dave457]

I usually get the radios that were probably built on Monday morning or Friday afternoon.

 

[BC Coyote]

I usually get the radios that were probably built on Monday morning or Friday afternoon.

I seem to have that same problem but with cars and trucks............

 

[DelR]

I didn't do anything no different than I do to other 29s, this one just turned out this way. Lucked up...

Actually, I am remembering back in the 90s I knew a couple people that were getting 27-30 swing out of cobras. One was a cobra 25 and sounded great.