Start here and see if you can find the manual:
Dual | Manuals Free Download, Owners, Service, Schematics, Brochures | Vinyl Engine
I didn't see the 604 listed, but it might be very similar to another there, but with a different case color or something. Take a look around and see what you can find there.
You'll want to give the turntable a little tuneup. Replace the belt (if it has one - I'm not familiar with your deck) and change the bearing oil. Use Mobil 1 synthetic automotive oil - the 5W-30 is terrific for turntables and a quart will last you a lifetime.
For a stylus, you can find a replacement here:
Needle Doctor
or here:
Garage 'A Records: Phonograph Cartridges and Needles, Record and Vinyl Accessories, Turntable Parts and Accessories and More!
If you want to go with a new cartridge, my two favorite budget cartridges are the Grado Black and the Shure MX97E.
You'll also need a phono preamp to use your turntable. A phono preamp is different from a regular preamp or tuner. It's a long explanation, but records actually attenuate part of the low end to keep the groove a consistent size and to get the most music on each side. A phono preamp boosts the part that's been attenuated to make it work again. The cheapest new phono preamps are about $30.
Another option is to look for a used receiver. If it has a button or switch marked "phono" (or similar) it probably has a phono preamp built in. Ask your friends and family if they have an unused two channel receiver. Also look at Craigslist, garage sales, thrift stores, junk shops, and sometimes pawn shops have good deals on them. Receivers sometimes make excellent headphone amps, too, so take your headphones along and give it a listen before you buy.
Speakers are another matter. Sometimes you can find good used ones, but 99% of them are just garbage. Look for good brands on Craigslist, but a lot of people look there. The cheapest way to great sound is building your own. The easiest, least expensive (and very good!) speaker is probably the Voigt Pipe. Here's the resource page:
https://mywebspace.wisc.edu/jstalnak...tPipeSpeakers/
You can find nice Fostex singledrivers at Madisound (
Madisound Speaker Components | Assisting speaker builders for more than 25 years.) for not too much. If you don't have access to tools, see if there is a woodshop at a nearby school, a lumberyard, or ask friends and family if anyone they know has a tablesaw. These can be cut and assembled in just a few hours. There is no crossover to build - just hooking the +/- to the corresponding binding posts.