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Cobra 29 W/RFX75 ???

Delmar

Member
Feb 11, 2012
11
1
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I am running the above mentioned radio. What linear amp would work well with my radio set up to get another 100-150 Watts ??? This will be going in a truck FYI.

Thanks for your help(y)
 

I am running the above mentioned radio. What linear amp would work well with my radio set up to get another 100-150 Watts ??? This will be going in a truck FYI.

Thanks for your help(y)

well considering your radio will have roughly 100 watts swing drive .you will need a amp
thats has 8x2879 or 12x2879 anything smaller and you,ll blow it up
 
Is that what is called the Whack Pack or Super Whack Pack ?

If it is need to read this

http://www.worldwidedx.com/cb-band-cb-radios/22687-radioactive-wack-pack-unveiled.html

NO. The RFX-75 is an external mosfet final section that goes on the back of the radio. It's like a small amp, has nothing to do with this whack pack crap. They have been out for several years now and many shops are doing mods with them.

RFX-75 Install in a Cobra 29 Black Chrome - YouTube
 
I am running the above mentioned radio. What linear amp would work well with my radio set up to get another 100-150 Watts ??? This will be going in a truck FYI.

Thanks for your help(y)

Since the radio now does 100-120 watts peak there is no way you can run a small amplifier that only adds 150 watts. You will need an amplifier that can handle the power your radio does. Something like this below will work.

You must decide on what you want. Either you have a basic peak and tune done on your Cobra 29 good for say 20 watts. Then get a small amp like a Texas Star 250 and you get 200-250 watts.

Since you decided to hotrod your radio simply put you need a big amp. Probably be in the 700 watt range.

TNT 600hd

Transistors 4 x 2SC2879
Dimensions H 4 3/4' x L 11' x W 6 3/4'
Amp Draw (maximum) 100
Class B biasing
SSB Delay yes
Pre-amp yes
Driver Required TNT 250 (optional)
Power Output (RMS) 300 Watts
Power Output (PEP) 625 Watts
Driven Power (RMS) 400 Watts
Driven Power (PEP) 1000 Watts
install recommended with 4ga wire
and 125a fuse. Max input carrier of
20w or 300w max carrier from amp.
Max peak input 240w.



Price: $375.99


http://www.xforceamps.com/category/TNT-35
 
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If you are getting 100 watts out of your RFX-75; then you are over-driving it anyway. No more than 70 watts power out of it with a small fan mounted on it is all it was really designed to do.

If you ran a 150 watt amp with it, it wouldn't be any real change at all anyway. Besides that, a 150 watt amp has a very low input power requirement of no more that a couple of watts/AM - tops. You might as well put your radio back to stock for what you propose to do in this case.

If you must run an amp with it; then turn the power waaay down on the radio. Make sure there is no more than 100% modulation out of the radio too. Then you might be able to hook it up to a Texas Star 500. They can take up up to 30 watts input power; but they really should have no more than 25 watts input for best results. You will need to have a variable power pot added to your radio - if it doesn't already have one.

It takes four times the change in power just to read a 1 S-unit change at another radio station's receiver. So, going from an RFX-75 @ 70 watts output would need to have an amp with 280-300 watts output to get just one S-unit of gain. A 150 watt amp would only see a 1/2 of an S-unit of gain change. Not really worth it - IMO. Using a TS-500 would see about ~1 1/2 S-units of change.
 
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I understand Robb, but in the Cobra 25/29 radio's most every shop is getting 100 ish watts from that mod. SSB radio's are around 70-80.
 
I understand Robb, but in the Cobra 25/29 radio's most every shop is getting 100 ish watts from that mod. SSB radio's are around 70-80.
Yup.
They do it all of the time - so I've heard. But in reality, the ERF-7530 wasn't made to be pushed beyod spec sheet specs like a bipolar 2290 can. The track record of MOSFETS used in CB/Export radios isn't all that great. Very sensitive to SWR changes for the worse too. I ran my S-45 non HP for a year or more @ 50 watts and never had a single problem. Turned it up to 70 for just a week - then 'snap, crackle, and pop'. Sure, they are cheap to replace. But who needs the aggravation for just a couple of extra peak watts - that no one will ever hear or even be able to tell the difference of anyway?
 
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Thanks for all the reply's boys. I'm new to modding CB's, learning slowly but surely. I'm going to leave this Cobra 29 RFX 75 alone and see how it does, I finally got it installed today after it sitting on the bench for a couple weeks.
 
I am running the above mentioned radio. What linear amp would work well with my radio set up to get another 100-150 Watts ??? This will be going in a truck FYI.

Thanks for your help(y)

my 29 lx le with rfx 75 only shows 55w on the dosy4001, i run my dk @2w and swing 55w using a ts dx500v with no problems. 2w dk, shows 160w dk on amp, and swings to 600w. Not sayin this is right or wrong, but thats my set up.
 
Sounds good. With that radio it would be a good idea to power it straight to the battery with say #10 wire. Reason being it will draw more amperage by adding the RFX unit.
 
I am running the above mentioned radio. What linear amp would work well with my radio set up to get another 100-150 Watts ??? This will be going in a truck FYI.

Thanks for your help(y)


If you wanted more watts then a RFX-75 was a real bad idea. Set the dead key at 10-15 watts key and drive it into a 4 pill such as a TNT 600.
I hate the RFX-75 as much as I hate dry shaving with a dull razor.
 
Rob are you saying if the rfx-75 isnt over driven and used with moderation like it should be its a good add on for 20-30 watts more
 

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