looking for info on how to do the IRF520 mosfet upgrade to a cobra 25ltd classic st. need info on the parts and the installation. and what i should expect on the output after the installation. then i'm gonna do the swing kit utilizing the cap and the resistor. gonna set it up to use it with a killerbee 250hd linear. thank you.
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cobra 25 ltd classic st/mosfet
- Thread starter jbenally33
- Start date
Look for an IRF520 - same thing. They're all over ebay
IRF520 TRANSISTOR TO220 PKG 1 PER PACK - eBay (item 320336434405 end time Mar-30-09 13:31:37 PDT)
IRF520 TRANSISTOR TO220 PKG 1 PER PACK - eBay (item 320336434405 end time Mar-30-09 13:31:37 PDT)
cobra 25/mosfet
what else do i need with the IRF520. I wanna order it all at once if i have to. thanks again for all the info.
what else do i need with the IRF520. I wanna order it all at once if i have to. thanks again for all the info.
Are you going to do this work yourself? If so good choice in radio's since it's a soundcrapper. If you are going to pay for the work I would sell the soundcrapper and get a better version of that radio.
Thanks for the info 555! I have a Cobra 25 from a HAM swap for a $1 and the mod was done to it, tx sounds like trash! I will use the info to fix the mod or reverse it.... 
mechanic
mechanic
That is very
true and that is the first question I always forget to ask myself whenever I look to these forums for tech tips
Seems like one could install it as a final with the proper modifications to the circuit.
Woof...
Woof, woof...
It's a little slow...
Even the Gate Capacitance is prohibitive can't pull that off (Charge Rate)
These work great for Stereos - even AM Stations - but nothing more than that - spacings of the Gate - to - Substrate - to - Junction spacing is pretty high - so that limits the Maximum Useable Frequency of this device (It's self-resonance) to much lower than the 27MHz.
Part of this devices design that prohibits the use in 27MHz is the REQUIRED substrate Reverse Characteristics - one main one being the reverse breakdown - or it's one way working value when placed in a circuit with bipolar constants - like AC or Audio Signal - - this prevents the device from working otherwise in a Class B amplifier or Class A - crossing over - when it shouldn't - which would have disastrous results for the equipment downstream from it.
It's 500V so the "spark gap" it needs to make this rating - works against the MUF you want - which makes the IRF510/IRF520 so appealing - less capacitance too from that closer gap.
Woof, woof...
It's a little slow...
Even the Gate Capacitance is prohibitive can't pull that off (Charge Rate)
These work great for Stereos - even AM Stations - but nothing more than that - spacings of the Gate - to - Substrate - to - Junction spacing is pretty high - so that limits the Maximum Useable Frequency of this device (It's self-resonance) to much lower than the 27MHz.
Part of this devices design that prohibits the use in 27MHz is the REQUIRED substrate Reverse Characteristics - one main one being the reverse breakdown - or it's one way working value when placed in a circuit with bipolar constants - like AC or Audio Signal - - this prevents the device from working otherwise in a Class B amplifier or Class A - crossing over - when it shouldn't - which would have disastrous results for the equipment downstream from it.
It's 500V so the "spark gap" it needs to make this rating - works against the MUF you want - which makes the IRF510/IRF520 so appealing - less capacitance too from that closer gap.
Could be done if you re-engineer the entire final section of the radio. But why? It might give you an extra 10-15 watts but no one will notice. Your best improvement would be to add a small amplifier like a Kl-203, KL-200, KL-300, or any other small 2 pill amplifier.
Here is a nice chart to consider. In order to gain 1/2 of an S unit you must double your power each time.
cbradiomagazine.com
Here is a nice chart to consider. In order to gain 1/2 of an S unit you must double your power each time.
Power in Perspective | CB Radio Magazine
POWER IN PERSPECTIVE - CB WATTS AND DISTANCE In today's CB world being heard by someone else on the radio can be difficult. There is considerably more interference than there was 20 years ago. CB radios themselves aren't really built to talk very far but many CB radio enthusiasts modify their...
cbradiomagazine.com
i find doing the TIP120 var dk with a mosfet, i find that putting a 4.7k from the +8v switched tx line makes it all play nice together. the class C setup on the FET depends on the carrier to work. i have a 66xl and i can clean swing from 20mw to 25w