cobra 200gtl

[cbrules]

I was told that the cobra 200gtl could be made to swing up to 150 on am.
Is there a mod for this? An could someone share the info? Also I could
use the modulation mod and the channel one to. I just want to do it right
the first time.
Thanks

[Unit 67]

Hi at all;I have a Cobra 200GTL-DX in my Bench.The radio is the lastest edition,because he came with the final transistors 2SC2290S.I did the all modifications in my radio,but this radio has just 95 Watts dead key and swings 130 Watts in my Bird meter,but the audio sounds "Muffled" in the AM mode.I have to leave the dead key at just 75 watts,and now sounds great.This radio came from the factory completely out of frequency in the SSB modes.Another thing in this radio is the aligment of the frequency counter.If I place the clarifier in the center,the frequency counter is off of frequency about 3Khz.Hmmmmm!!!!!! I have to align the frequency counter too,and the 10 Khz switch in my radio does not work!!!!!! I really dont know if it is for the Channel expansion modification,but the 10Khz switch not works in my radio.The audio in the RX mode is pretty bad too.This is couple of things that I found in my Cobra 200GTL-DX until now.I am going to fix all of those problems in my radio,and I let you know the results.


Unit 67-Puerto Rico

[Unit 67]

CBrules;I leave the info for the modification in your PM.








Unit 67

[Unit 67]

Now, when the radio warms up the radio has just 10 watts of output.I think this radio is a "Lemon". I have another Cobra 200 GTL-DX unmodified and I did the test and when is warm up the radio losses the output power,but just in the Hi Power.







Unit 67

[marv]

Would any care to share the power mod please. ?

[haans_gruber]

Let's cover a few topics on this to dispell any myths

The 2SC2290 transistor is capable of 60 Watts.
You could "dead key" an AM carrier with this much power but, there would be no room left to modulate it. Depending upon whether it's high or low level modulation in the 200GTL DX. If it is High level modulation 30 would modulate to 120 which would be 100% modulation. Low level modulation it would be 30 modulated to 90 which would be 100% modulation.

Use google: to search for the Toshiba 2SC2290 transistor specs in PDF
or you can find it here at the time of this posting:
http://www.qsl.net/df7tv/datasheets/2sc2290.pdf

You will find the radio operates within these specs.
minor changes will make minor differences, increase heat and only shorten the life of electronic components and thus the overall life of the device.

1.) There is no fan to cool the transistors/heatsink
2.) Doubling your power output is a 3db increase and makes an audiable difference only
3.) It requires a 4 X power increase to increase your signal by 1 S unit, or 6 db (100-400 -- 400-1600 -- 1600-6400 watts output) etc. You get the idea.

You are placing additional strain on a device for no practical gain in performance.
No one will ever notice a difference between a stock radio and a "tweaked out" radio. If they do, and/or say they do, it will not be much. Theortically, there won't be any appreciable gain.

The other consideration for base operation experiencing "muffled" audio is: the power/amperage requirement for the radio. Typically a 100 watt radio requires 20 Amps. If you can run the radio on Low power and not on High power. This is possibly an indication of a power supply lacking the necessary amperage to run the unit at full power output. Mobile operation: Possibly a wire gauge that is too small to handle the necessary 20 amps of current. Consult the electrical standards and specifications for the proper wire size/gauge and length.

One other possibility is to replace the 2SC2290 transistors with a matched pair of 2SC2879 transistors which are rated at 100 watts PEP each.
Go here to download the datasheet in PDF format: http://www.datasheetcatalog.com/datashe ... 2879.shtml
However, there may be some changes required in the circuit design in order to allow for this exchange. RF Parts in California sells the matched pairs and can probably answer any questions you have about the circuit changes if any are required and may even be familiar with the exchange proceedure. The matched pairs are about 45 FRN's U$.

http://www.rfparts.com/



Note: 25 Amp fuse in the lower right corner below the red power wire in the above photo.

I hope this is helpful.

peace,

haans

[Intrepid]

This radio looks pretty nice, I thought it would be like a Galaxy or something like that, but due to the audio output is not something that I would use or recomend. Seems that nobody wants to point at the audio limitter for this equipment.