a KEY DOWN radio, or a TALKING radio? i haven't seen a RADIO specifically built for key downs in a LONG TIME. 99% of the time they USED TO BE cobra 29's, but i NEVER used a 29, always used a grant XL, was never serious about winning, just did it because it was suggested i get in there & see where i stack up. never won anything, nor did i care, but i got farther then many thought....with a 'basic' XL. that i modded. and NOTHING spectacular. i even used an ar3500 in the 8 pill class, with ONLY the radios 2x2290 built in amp driving the big box. and also went far. talk back in a key down radio? why? for that matter, i never saw the reason for a talkback in ANY radio. more annoying then anything. as for receive upgrade...i've never seen a 29 receive better then an XL. i've only known a very very few key down guys that didn't talk skip regularly, so the skiptalkers usually used the same equipment for talking as for keydowns....many with voltage backed down for more keydown-time ability on skip.
that said.....i don't TRUST ANYBODY anymore to do 'power, audio, etc' mods on CB. i use grant xl, ar3500 or ic706mkIIg backed up with whatever amp setup is required for whatever i want to do. none of these radios has ANYTHING hairy done to them, and i even backed OUT some of the NPC-RC mod in the XL & 3500. why? those 2 radios actually come with GOOD QUALITY audio CAPABILITIES from the factory. they are DECENT radios. why BUTCHER them? and they sounde BETTER then when 'butchered', even when the 'butchering' is the standard 'hi-po' mods. 2 pill vs 2, 4 vs 4, 8 vs 8, 16 vs 16 & AC vs AC, i have never been blown away by ANY radio with ANY alleged mods, whether it be 'super wack packed, dusted, RR'd' or whatever other dumba$$, high dollar, waste of money mod somebody invented to get 250 watts out of a single 2sc1969 or irf520 or any other transistor.mosfet ever known to man. i have a cobra 29 that i swapped the final in.....20 years ago when i read CB Tricks II by medicine man.....and then i added the diode dial-a-watt mod. i use that radio as a comparison radio 20 YEARS LATER!!! it keys 8 watts on a coaxial dynamics, and swings to 14 watts RMS on the CD. it ONLY swings into the low 20's on the CD with the PEP mod. that radio has almost perfect audio signal as measured on a pro spectrum analyzer or scope. that radio has SMOKED any 50-60-70 watt dumba$$ modded 29 EVER. sound, clarity, keydown next to each other. whatever. REAL 8 carrier watts beats fake 50 watts every time. put a QUALITY rfi filter on it, still does 8 watts. put the filter on a 60 watt 'wacker' & it drops.
joe from davemade nc? i like joe. he tells it like it is. you ask a dumb question, he doesn't wanna deal with you. if you hafta ask a (DUMB) question, you shouldn't be doing it. at least not yet. he's not a teacher. he doesn't have time for that and lets you know that in no uncertain terms. on the other hand, he builds cheap amps, from a few dollars worth of parts, sells them at market value....which is WAY TOO MUCH....from an ancient, cheap, cheesy design. he is NOT up to date on radios, or their lack of new technology.....so, again, NOTHING against joe, i would NEVER take ANY radio advice from him ever.
you need to build the radio from the amplifier backwards. don't mod a radio & then set it up with an amplifier system. you want 16 pills to key 600 watts & swing 2400 on a standard vehicle 13.8v system? neatly & efficiently? put a (relatively CLEAN) 5 pill in front of it, that will get the 16 to do just that by building a smooth, clean cobra 29 that keys 2-3-4 watts, no diode butcher job and swings just right with a QUALITY mic (or processor or compressor) just notched up enough to give smooth, full audio. you'll sound a WHOLE BUNCH BETTER then 99% of the joker wannabe's out there with background-noise-filled, crunchy, overmodulated, over-echoed crapola audio.
or is that not what you asked ;-)
...runna pile-up on 6m SSB