Cobra 29 Tuning and Amps

[Duster]

Howdy everybody. I have 3 options for tuning my cobra 29LX.
A. 4w carrier swinging to 25-35,
B. 5w carrier swinging 38-45,
C. 15w carrier swinging 75 (rfx-75)

Which amplifier would you recommend for each setting? Maybe an Xforce Mosfet 400 for option C? what about A and B? Any help is apprieciated.
Thanks

 

[Robb]

The kind of amp you choose will determine the kind of settings/wattage you use.
It will also depend how the radio is modified.
e.g: With or without an NPC/RC mod

An AB class amp is cleaner sounding than a C class amp. Many of the ch 6 guys do the C class amps. The C class amps have a very dirty output and require a higher input wattage. Very dirty though; throws off nasty harmonics. The AB class amps are mostly used by SSBers, and they also work on AM - but not as loud or distorted.

 

[psycho]

The kind of amp you choose will determine the kind of settings/wattage you use.
It will also depend how the radio is modified.
e.g: With or without an NPC/RC mod

An AB class amp is cleaner sounding than a C class amp. Many of the ch 6 guys do the C class amps. The C class amps have a very dirty output and require a higher input wattage. Very dirty though; throws off nasty harmonics. The AB class amps are mostly used by SSBers, and they also work on AM - but not as loud or distorted.

You are judging class c amps on the way they sound on channel 6??? I thought you knew better than that, the homeboys on channel 6 drive 3 pills into 6 pills so I guess all class c systems are nasty. Drive a class c amp easy and they are just as clean as a class AB.

Garbage in = garbage out

 

[Robb]

Not so much a judgement than it is an observation.

C class boxes aren't set up to drive the transistor/device in a uniform/linear manner. The AB class is more linear. The result of the non-linear condition is distortion and harmonics. When the amp design flies in the face of the device characteristics; what can one expect?

At least, that is what I have learned.

 

[AudioShockwav]

Even if you reduce the drive it is still there no way to get around it. The distortion is caused by the gap that is there in the collector current until it gets past the threshold and it becomes even more noticable if you know what to listen for. You can get by on AM mode with it but on SSB it is a crunchy sound.
This the oldest argument in the book in between the " class c comp" guys and the rest of the radio world.

73
Jeff

 

[GnG8d]

Drive a class c amp easy and they are just as clean as a class AB.

Oh really? Then whats the benefit of one over the other?

 

[Duster]

OK guys, then what amp would YOU personally run if you had a radio tuned to one of the settings?
Thanks

 

[Robb]

OK guys, then what amp would YOU personally run if you had a radio tuned to one of the settings?
Thanks

Well, a Texas Star 350 amp is an AB class amp, so long as it isn't being over-driven. Over-driving it will lose the amp linearity - which isn't desirable.

The 350 wants to see no more than 20 watts input for full AB class amp output. So, the radio needs to have an output of no more than 5 watts dead key and 20 watts peak power.

If you aren't seeing a 4:1 ratio between the dead key watts and the peak watts; then the radio has more than 100% modulation. That is bad. No more than 100% modulation is necessary to keep the signal out of the radio fairly uniform. You may need to turn down the modulation until you see no more than 20 watts peak @ 5 watts dead key. This will ensure that you aren't feeding the amp with distortion and harmonics that will cause a 'crap in = crap out' situation with the radio AND the amp.

Even if you don't run an external amp and use just the RFX; the same rules apply.

If the radio has been modified with the NPC/RC mod; then the situation is not the same. You will still have to tune the radio's output for no more than 20 watts output for the TS 350. The modulation adjustment will be more difficult to do correctly. With 200% modulation with the NPC mod; the dead key should be 2.5 watts and the peak watts will be 20 watts. Because at 200% modulation, the correct ratio becomes 8:1 with the NPC mod. If you don't have the NPC mod in your radio; then forget about this paragraph.

Does that help you understand some?

 

[9C1Driver]

Howdy everybody. I have 3 options for tuning my cobra 29LX.
A. 4w carrier swinging to 25-35,
B. 5w carrier swinging 38-45,
C. 15w carrier swinging 75 (rfx-75)

Which amplifier would you recommend for each setting? Maybe an Xforce Mosfet 400 for option C? what about A and B? Any help is apprieciated.
Thanks

Duster your thread here has gone off on an amplifier bias debate. There are plenty of links and threads for that. That said here are two amplifiers that will work depending on what tune or setting you choose on the radio.

TNT 350hd

Transistors 2 x 2SC2879
Dimensions H 4 1/4' x L 7 1/8' x W 41/4'
Amp Draw (maximum) 29
Class B biasing
SSB Delay auto
Pre-amp yes
Driver Required N/A
Power Output (RMS) 150 Watts
Power Output (PEP) 400 Watts
Driven Power (RMS) N/A
Driven Power (PEP) N/A
install recommended with 8ga wire
and 50a fuse. Max input carrier of
5w or 120w max carrier from amp.
Max peak input 120w.



Price: $232.99


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
******************************************************



I think you could also make a Texas Star 500 work as long as you went with a lower setting on the radio.

 

[Duster]

Does that help you understand some?[/QUOTE]

Yes Sir I think I am starting to get an idea. I have used barefoot radios for years, and am just now starting to learn about amps. Thank you for working with me. I will eventually get it all figured out.

 

[Duster]

Duster your thread here has gone off on an amplifier bias debate. There are plenty of links and threads for that.

Yes I see that That wasn't my intentions in starting this thread. I really just wanted some ideas of amps I could drive with depending on the options I listed.

So THANK YOU for listing some amps! So would the TNT600 work with the RFX-75 setting?
Thanks.