I have the factory AM music master radio in my 70 challenger and was told there was such thing as a am to fm converter. Where would I buy such a thing and about how much should this cost? I'd like to keep a stock look.

Ebay, Radio shack, amazon, etc. Do an online search you will find all kinds of places.

eBay or a flea market. There's a chance that the capacitors may be dried up, but they are easy to replace. $10 to $20 I would guess.

They stopped making them about 25-30 years ago, but , they are pretty easily found on the internet .If you look on E-bay for example you can usually find about a hundred on there at any given moment, some even new in the box . Prices range from $ 25-$ 75 depending on the brand ,the number of bidders, etc.
With original FM radios going for anywhere from $ 200- $ 1,000 or more(depending on year/make/model)
and having your AM radio converted to FM costing in the $ 450 range ,
These old vintage FM converters are Without a doubt ,the cheapest way to get FM .

Greg

i was to cheap to buy an old converter co i wired a jack into my AM radio to play music off of my phone.
i found this site, link
parts cost less than $10

A buddy of mine found one in his dads basement in the box never wired up. Got it for free still works and that was about 5 years ago. That is in my 74 GMC truck. If you arent really a fan of trying to tune in with two dials, I suggest redirad and they hook up really easy and you can use an Ipod or any MP3 player and listen to the wolfman jack shows like I do in my 69' RR!!

I still have one of them "Standard" stereo converters. Hooks up like a regular fm conv but has an extra speaker wire so you add a rear speaker or whatever. Stereo light and all. It has a volume knob too that just controls the added speaker IIRC.

Yes, e-bay or flea-markets would be good sources. I have run FM converters since the 60's and in one car I have a Radio Shack one I bought in 1990. Frequency response is slightly better than AM but the problem is lack of selectivity. The FM band is so full now it's tough to tune and hold a station even the high power guys. Go with a newer radio or conversion that gives good selectivity.