a few thoughts...
go here for a lot of tuna info, including where to find bill ammons, & a few other modders & techs as well:
http://www.fmtunerinfo.com/i would also recommend joseph chow, who adwertises on agon, & mike williams, who goes by "punker-x" on audiokarma.
http://www.componentplususa.com/http://cls.audiogon.com/cgi-bin/cls.pl?misctunr&1193808148http://radioxtuners.com/awoid don scott like the plague; he does not use proper test equipment to service & align tunas, & if yours comes back from him sounding better than when you sent it in, it's dumb luck. i know of several folks who had to send their tunas elsewhere to get fixed after he butchered them. i would also awoid ed hanlon - he's a nut job who will werbally or in writing tear you a new orifice if you ever should so much as question anything he might be doing tech-wise, & go into a psychotic rage, accusing you of trying to 'steal his secrets", which is a joke, cuz there's so much info & help awailable from folks more than willing to assist anyone who might be interested in diy. again, i have heard this happen to quite a few other tunaholics... and, besides, he subs all his work out to another shop anyways, so why not deal directly w/the tech, instead of paying additional mark-up to a middleman? ed's antennas
are first-rate, fwiw...
using a car stereo can be a good way to go; this topic has come up every so other on the fmtunerinfo site's yahoo tuna forum. the only thing to be aware of is that sometimes you may have what you think is a quality quiet stereo signal, when in fact many car stereo's automatically blend towards mono when signal strength gets weak, so you may not be hearing full stereo w/compromised signals.
as far as money is concerned, while i have a lot of tunas, when money gets tight, it's easy for me to unload a tuna or three, w/o losing any money - prudent used shopping means you will at least break even when you wanna sell something.

re: the da-f10 (in the da-c20 tuner/preamp), while it is not as good a tuna as the da-f20, if you do not like the sound of yours, it likely needs a refurb, or at the wery least an alignment, as it really
is a nice sounding tuna in its own right.
re: the m-d tunas - easily the most overhyped/overpriced tunas around, imo - about any tuna i own will be at least as good, & likely better than m-d's former best, (the $6k md108), in sound quality & reception, except where i noted reception issues. i don't have any reliable info on md's latest $9k tuna, so mebbe it's a winner. personally, if it were my money, & i could afford it, i would be more wanting to try the new $4.5k accuphase t1000 - i hear its outstanding, especially when run thru an outboard dac from its digital output. unless i can find one used at a great price, this one is outta reach for me.
re: the sonics of the kt7500 (which
does have excellent reception), yust look at one person's take on its sonics: jim rivers, who did "shootouts" of 84 (?!?) tunas, over at the fmtunerinfo site, found it came in at 79th spot, out of the 84 he listened to. even tho it's about his fave tuna after mods. this corresponds w/my experience w/a kt5500 (slightly below the kt7500), & also a kt8300 (slightly above the kt7500). of all the tunas i have owned over the years, only the kt8300 & a refurb'd mcintosh mr77 wouldn't be acceptable as a daily use tuna for me, based on sonics. i would even prefer my old adcom gft1a or a m-d ft101 (which are both yust ok, & quite comparable to each other, in stock form, imo...) yes, i
did own a bill ammons modded kt7500, & it
was a stellar sonic performer, if not the best tuna i owned in terms of ultimate quieting ability. if you don't wanna diy (there
is excellent info on diy'ing the kt7500 on the fmtunerinfo site), bill ammons is wery reasonable - i suspect he'd charge somewhere around $250 for a refurb & mod of this tuna... if you get it modded, & have an excellent radio station in your area, you may surprise yourself at how much time you may spend, enjoying listening to it, even in the sweet spot, doing serious listening. aa
happy fm listening!
