Cobra 29

[heranney76]

Hello guys looking for input for mods for my cobra 29 ltd classic. I have swapped out my final for a 1969 and already has a 2314 driver. Looking to get most out of it barefoot. Plan to get it aligned and peaked soon. Thanks in advance.

[MDYoungblood]

Actually changing the final will only gain you a watt or 2, not enough to see a difference on the receiving end. Other than modulation I really don't know any mods that doesn't require some other things, channel board, etc. What else are you looking to do?

3's

Greg

[heranney76]

Was looking to get most watts out of it I could but didn't know if other components needed changed as well

[BrownDogAudio]

When you replace the final with a 1969 final you need to make sure you re adjust the bias (it WILL change). You also should change out the driver to a 2166 if at all possible. These two work together much better. If you haven't already, installing a variable, or setting the dead key to about 3/4 watt to 1 watt, will really open up the swing, and allow for much better modulation. You should also upgrade your Voltage Regulator for better voltage stability, as well as set your power supply to about 14.1 VDC. I absolutely DO NOT recommend cutting the diode on the AMC. This will do nothing but overdrive your AMC circuit unless you have beefed up your Audio IC and done a full recap replacing all your 10vdc caps with 16vdc+ caps. You will see better numbers by over-driving the AMC, but when you put it on a scope, it will look like garbage. Shark teeth and flat caps all around. The most you will ever see out of a 1969 is 20 watts PEP. More if you have a DOSY, lol

If you really want to get the most out of a Cobra 29, I would suggest doing a MOSFET final and driver swap. When biased and aligned correctly you can see a 1 watt dead key that will swing 28-35 watts PEP. I know this for a fact. I have done at least 15 of these for customers here in the shop. Just keep in mind that bias and voltage are VERY important with a MOSFET. And heat-sink compound is your friend. MOSFETS run HOT. So making sure they don't get to hot is key.

Good luck!!

[heranney76]

Thanks for the reply browndog I guess there's a mosfet in my future. Got a 29 nw wx st on the way (too good of deal not to pass up) going to do mosfet swap tip120 variable deadkey and a rfx95 to it. I did discover a recieve mod from pin 14 to c12 that helped the receive alot well if you can barely hear someone flip it on and you can hear them better. Probably put those pieces in the nw and send it off somewhere to have alignment and tune up done to it.

[BrownDogAudio]

That sounds good heranney76! I didnt mention the c12 mod because you had asked about power, but that is an awesome mod. I have all my 29's done that way as well as most of the 29's that come through the shop. I usually try to use a front mounted switch for it. I do have one piece of advise, if your planning on running the nw st version of the 29 for a long time, keep an eye on the night watch, sometimes the transformer can go down and send upwards of 50v+ back through the radio. And keep and eye on the WX board in it. Unfortunately they tied everything in the radio through that board. So if it goes down, the radio is a real pretty paperweight.

[heranney76]

Good to know browndog I used the channel 9 switch for the pll mod. Surprisingly it took some digging to find it not a super common mod i could find. I know the sound tracker isn't the greatest thought about disabling it using st button for rfx95 switch. So being everything is tied into the wx board I would guess no way to disable it? Also is it possible to put diode on nw circuit to stop it from happening?

[BrownDogAudio]

let me see if i can answer these without loosing track...

The Cobra Sound Tracker only works with another Cobra radio that has sound tracker. Kind of unless honestly. I would un-solder the switch and use it as a switch for something else.

If you are going to use an RFX board, i would suggest you just go with a 1969 final 2166 driver, because the MOSFET final will be way to hot for the RFX board. They are usually low drive to the best of my knowledge.

No there is no way to disable the WX board on a WX ST radio unfortunately. It is an integrated FM module and for some reason Cobra decided to tie RX and TX through it...just stupid. Should have been a standalone module. I'm sure there is a way to isolate it to remove it, but just to be honest, that's above my pay grade. I have no idea how to do it.

As far as a diode on the high voltage transformer, that sounds like it would work. Ive never personally done it, but in theory that should work. Obviously a diode is like a one way valve for electricity. I will have to look into that further. Nice idea!!

[heranney76]

Sorry for the confusion yes going to use the st button for the rfx board. And good to know about them getting to hot. Thanks again browndog

[BrownDogAudio]

yessir, anytime!