Tuesday, February 22, 2011

Classic Radio now with mp3!

As mentioned previously, I have been fixing my radio for the sole purpose of hacking it. Now that it is functional, my goal is to be able to connect an mp3 player and listen to it in the truck.

The easiest solution would probably be to use a transmitter but I have two problems with this. First, there are about a billion FM transmitters on the market but I have yet to see an AM solution. Seeing as how my old radio is AM only this does not work for me. Second, I have witnessed first hand just how poorly those transmitters perform. They are prone to fading in and out, shifting, and all sorts of other pesky problems; this is not the solution for me!

I know there are multiple ways of going about this, so I had a few qualifiers in mind when I first approached this problem:

1) Easy to implement
2) Cheap!
3) Reversible

Unexpectedly, I stumbled on a perfect solution here. The original poster's explanation left a lot to be desired but forum member gryzynx clarified a number of details and helped me out with the component selection (I am poster ronilevi obviously).

I purchased the 3.5mm jack for $0.50, scavenged the appropriate cable, and hooked it all up. I had a few mis-steps of course (I thought I fried my iPod a couple times), but it was really just as simple as two wires to hook up:

I will have to implement a more permanent solution but, at least for now, I know this works! As a bonus, here is video of it functioning:

Please note and observe the forum warning to not have the mp3 player charging while it is hooked up to the radio.

The Radio in Action!

Here is a quick little video of the radio fully functioning (I caught a good snippet of Otis on the air). It will sound a lot nicer with a real antenna attached.

Also, I have noticed that the volume and tone knobs are scratchy. I will have to spray this down with contact cleaner and hope it works itself out.

Thursday, February 10, 2011

Easy Fix on the 1966 Ford Truck Radio

The '66 Ford Truck is keeping me busy! There is plenty of work to do but I have been having fun playing around with the radio I picked up on Ebay. As soon as I received it, I promptly yanked the cassette radio that the PO had installed and chucked it.

The first thing I did was disassemble the radio to expose the circuit board and check for any obvious signs of failure: burn marks, corrosion, etc. I was relieved to find that none of those were present or at least not obviously so.

Despite the internet's propensity for disseminating vast amounts of knowledge, I was unable to source schematics, but I did find some minor information on my radio.

Turns out that decoding the A4TBT stamp on my radio's box lets me know that it is a transistorized AM truck radio built by Bendix (or using Bendix guts) in 1964. Nice to know but hardly of much help to me.

I did some minor repairs so that I could get a speaker attached to it since it appeared that the originals had been yanked out and proceed to power the radio on. There was a very audible hum pumped to the speaker as soon as the switch turned on despite the volume level.

Here is where I noticed I had made a mistake: these radios are powered from a 12V battery, a DC source. While the power supply I had hooked up for testing was at the correct voltage, it was a switched power supply! These sort of power supplies are prevalent in today's electronics because they are more efficient but they are completely unsuitable for testing an old car radio. Instead of pulling the battery out of the truck to use for testing, I bought this power supply which is regulated, adjustable, and lends itself quite well for a future of electronics tinkering at my bench.

Reading up on old radio repair, it seems that the culprits in most hum situations are paper and electrolytic capacitors. Over time they dry up causing their values to stray. Inspecting the radio turned up only two capacitors that fit the bill so I made a really crappy picture in google documents and then removed them.

I ran to my local electronics store, picked up replacement electrolytic capacitors, and soldered them into place. The next power test (now with new capacitors and an appropriate supply) played fuzz but no hum! I was able to improvise an antenna out of alligator clips and a long strand of hookup wire to make a loop antenna and it picked up local stations!

Now that it is functional, it is nigh time to hack this thing!