I found this one, but I haven't verified it is correct yet. I need to come up with a list of parts, and I may as well recap. Any recommendations of where to order from?
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Cobra 25 unhacking project
- Thread starter 338_MtRushmore
- Start date
I felt like I had to rescue this little Philly after I read this ebay description:
Here a nice,powerful Cobra 25 ltd Classic, Got Variable to see zero deadkey & Echo board,1/2 swings to 18 easy,no mic or back plug in radio AS IS NO RETURNS make me a offer very strong radio, works alsome,had tech put in on bench,make someone a good talker or put in front of amp an turn deadkey down,talk all over .Happy Day USA STRONG,Smoke Free found a plug in I send but no mic I use it,An Fast Free Shipping Thank You
Here a nice,powerful Cobra 25 ltd Classic, Got Variable to see zero deadkey & Echo board,1/2 swings to 18 easy,no mic or back plug in radio AS IS NO RETURNS make me a offer very strong radio, works alsome,had tech put in on bench,make someone a good talker or put in front of amp an turn deadkey down,talk all over .Happy Day USA STRONG,Smoke Free found a plug in I send but no mic I use it,An Fast Free Shipping Thank You
Avoid eBay cap kits, unless you get 'em from KlondikeMike (A forum member).
While the kits have all the caps you need, if you don't go through a trusted seller often you get CheapChina caps on eBay..
http://www.mouser.com/
http://www.digikey.com/
http://www.newark.com/
The schematic you've found looks correct. Grab some 60/40 solder 1N4001,1N4003,1N4148 diodes, and a variety resistor pack.
Reads a lot like a joker would type...
I bet the seller did the work himself, no "tech" tested this thing..
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Thank you for sharing this, a "proper" variable dead key for the 25/29!
If I had this is the way i'd choose to do it
They still swing a lot I.m.o. unless you tune the "final inductor ferrite" (the one most people back out or toss away) 'till buried all the way down, then she almost does a 1:4 from 1 Watt carrier, otherwise it's "super-mod" & I'm not huge on that. Almost always I find they grossly overshoot 4 watts p.e.p., to me this is a swing kit more than a vairable d.k. And unless you go the extra tuning steps to ensure it won't bleed, this mod has produced "loud" results even with AMC pot backed all the way to the "min" position & I did not like those results.
This is my first year playing with a solder iron, so maybe I haven't learned how to properly de-tune these rigs (so they work correctly @ any dead key w/ this mod).
73
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That link incorporates variable power AND the swing mod - all in one. You can substitute up to 1000uf cap @25-35v. Most people use a 470uf and do not notice any difference if using a bigger cap; I did. Just my preference.
On a semi related side note, I installed a 470ohm resistor for talkback on 29 today, and it didn't work. Just a second of talkback every time I keyed, then it stopped. Is it just too much resistance, and I need to drop to 100ohm? At least I'm pretty sure it was 470. I need to work on identification skills
Is there a variable power mod that maintains a good swing ratio? I have never seen one, and it seems that most exports still swing hard from a low deadkey.
Sounds like it is intermittent/'bad connection'.
You can also hook up a 1kohm pot in series with that 100 ohm resistor to make the talkback - variable.
Also looks like this radio you got from that guy is going to need a thorough going-over.
You can also hook up a 1kohm pot in series with that 100 ohm resistor to make the talkback - variable.
Also looks like this radio you got from that guy is going to need a thorough going-over.
Any Cobra 25/29 is going to outperform an export radio in AM mode; the 25/29's just constructed for max mod by design. The exports only offer more power; not better AM modulation. Waste of time making an export try to perform like a 25/29 - JMHO . . .
I don't need/want a swing kit combined with the variable carrier setting, that's my issue.
I don't want the radio to exceed the proper modulation setting regardless of carrier setting, I guess it's becuase of the transformer modulated high level design.
Still I just want to set a Cobra 29 @ .5 watt and get 2 pep, then 1 watt to 4 pep, then 4 watts to 16 pep, this mod will NOT allow this in a simple twist of the knob.
Indeed the "swing kit" is combined with the variable dead key in this mod no-matter-what.
The only work-around is to re-tune the radio for the required carrier level, every. dang. time.
That's only because i'm anal about my signal, and I want to have a clean signal; (no matter d.k.) before it ever gets amplified.
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But you wanted to do that with a ept3600xxx chassis? All that cap is doing is allowing peak watts to get through. However, if you don't want it to swing, all you would need to do is not install that cap.
You won't see 20w from a 25/29; the stock final is only good for 10w. Anything over that will be distortion and/or 54mhz trash. Unless you install a MOSFET or 2sc1969 to get more watts.
All i'm saying is that I want my Cobra to have a variable dead key that doesn't screw up the purity of my signal (harmonics, over-mod, bleed-over) just because I changed the carrier adjustment..
You can set it up pretty well (TIP120 mod) to not be too bad on the scope, it takes a lot of tunning though and the more you adjust the carrier the more it "sways" from your previous config.My friend, I don't need any help on the exports, the ept3600 was from another thread, & I was trying to help somebody remove a modification, then the thread devolved into another thread, I attempted to explain the difference between NPC and swing kit. That's all, nothing more.
I don't like swing kits, I like variable power, some work better than others.
(The factory ones work the best).
I never said anything about 20 happy watts you brought that out of the æther, but yeah 16 watts p.e.p. gotten from a 2SC1969 all day long, drive it with a 2314...
Thank you for the clarity Robb, & I apologize.
Just do not use the cap, no swing problem got it!
73
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This has been posted before, i'll search for that thread.
My guess: Normaly a jumper is present, if you introduce resistance to this spot it limits the amount of current passing through and this lowers the dead key, if you parallel a capacitor with the resistor the voice peaks produce AC/modulation which passes through the cap and gives you "supermod", while at a low dead key because of the resistor.
Without the cap, you wouldn't loose the AC component at a low dead key, it's just that everything will be "current limimited" through the resistor and "smaller", the cap lets the "modulation jump"?!
My guess: Normaly a jumper is present, if you introduce resistance to this spot it limits the amount of current passing through and this lowers the dead key, if you parallel a capacitor with the resistor the voice peaks produce AC/modulation which passes through the cap and gives you "supermod", while at a low dead key because of the resistor.
Without the cap, you wouldn't loose the AC component at a low dead key, it's just that everything will be "current limimited" through the resistor and "smaller", the cap lets the "modulation jump"?!
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