29 LX variable power

[Nick23]

Hey guys,

I'm attempting to do a swing mod for my 29. 2 questions; for variable power they say you need 2 wires to run to the rf gain knob. What type/gauge wire should I use? Also, would a 30watt solding iron be sufficient?

Thanks

 

[222DBFL]

#14-#18awg or whatever wire size is being ised currently in the radio will work fine. Doesn't need to be large gauge. The run is short. Be careful when performing this mod, and yes the 30w iron should work okay, just let it heat up good, and tin all your wires before soldering them on. Use good solder as well. I use lead free rosin core solder myself. Use some thin solder as well with that iron. It will help with melting faster. JMHO. Be safe and good luck with the mod.

 

[Nick23]

#14-#18awg or whatever wire size is being ised currently in the radio will work fine. Doesn't need to be large gauge. The run is short. Be careful when performing this mod, and yes the 30w iron should work okay, just let it heat up good, and tin all your wires before soldering them on. Use good solder as well. I use lead free rosin core solder myself. Use some thin solder as well with that iron. It will help with melting faster. JMHO. Be safe and good luck with the mod.

Thank you for getting back. Another question for you, what does tin all you wires before soldering mean?

 

[222DBFL]

Tinning, or adding some solder to the wires themselves before soldering the connections is what I was speaking of.

 

[Nick23]

Thank you

 

[Grogan]

Find A friend that works on radios and can teach you a few things about electronics and soldering and radios and you will be happy that you did not toast a radio. live and learn.

 

[Nick23]

Got the swing mod done. Everything works great. Is the variable power worth doing for running barefoot?

 

[Robb]

Got the swing mod done. Everything works great. Is the variable power worth doing for running barefoot?

Not really.
You can; but you must consider that when a swing mod is done, it has changed the modulation from 100%/max to about ~150%/max. Which means that it is putting a greater stress on the final. If the mod was done right 1 1/2 to 2 1/2w isn't worth putting a variable mod in for.
A stock radio; yes . . .

 

[Nick23]

How would you do variable to a stock Cobra 29?

 

[Robb]

Not by using the RF Gain control with the resistor you used in the swing mod. Sure way to burn up that RF Gain pot. They cannot handle that much current and fail. Newbees do this all of the time and wonder why the radio stops transmitting after a while.

There are two ways: one is to put a pot on the pre-driver, and the other is to make a regulated circuit to control the voltage. Did you understand my previous post concerning over-driving the final after doing a swing mod?

IIRC; isn't there a known way of using the panel buttons on the LX model to make the radio do variable power? I have a vague memory of that; not quite sure any more. I usually work on SSB radios and don't really mess with AM only radios any more . . .

 

[sonoma]

here is a variable swing mod I like to use. change the 1k ohm variable to one you can mount out side the radio to adjust the output. this will save burning up any pots on the radio as Robb mentioned

 

[Nick23]

Not by using the RF Gain control with the resistor you used in the swing mod. Sure way to burn up that RF Gain pot. They cannot handle that much current and fail. Newbees do this all of the time and wonder why the radio stops transmitting after a while.

There are two ways: one is to put a pot on the pre-driver, and the other is to make a regulated circuit to control the voltage. Did you understand my previous post concerning over-driving the final after doing a swing mod?

IIRC; isn't there a known way of using the panel buttons on the LX model to make the radio do variable power? I have a vague memory of that; not quite sure any more. I usually work on SSB radios and don't really mess with AM only radios any more . . .

I didn't know about the rf gain getting burnt up. I read about it on cbradiomag, a site I usually trust

Would turning down vr4 or the mic gain help with not frying the final? I was just wanting to get my dead key down, not 150% modulation.

 

[Nick23]

Thank you too, Sonoma

 

[sonoma]

doing the mod I posted for you will not hurt the rf gain or any other control you use. this mod is why it was designed so the controls would not burn up from the rf going through the control.

 

[Robb]

I was just wanting to get my dead key down, not 150% modulation.

That is what a swing mod does . . . increases the percentage of modulation . . . If done right . . . I have used a larger cap for the cap part of the mod. CBRM used a 100uf/25v for his swing mod (common and acceptable) IIRC; but I've used a 470uf/25v for good measure . . .

Thanks Sonoma, for that regulated variable schematic . . . nice!