[dataway]

Digi-Key is amazing, they have tens of thousands of different components .. they will send you a single resistor if you want it. Every single item has specs, pictures etc.

But yes, more and more of the stuff is going to board mounted components.

[dataway]

Final tuning is done, using the procedure outlined in the Delco radio manual. Went in a text book fashion.

Appears to work as well as it did factory day one. Was kind of a weird experience listening to this radio that I haven't heard since around 1978 when it no longer worked well enough to bother using. Was very happy to hear a few AM oldies stations playing ... looking forward to hearing it driving down the road .... for at least a few minutes until I turn on whatever hidden modern sound system I install

Below is my impromptu electronics work area in a corner of the living room .. shop is kind of chilly for this kind of work right now.

Signal generator for creating the three difference reference frequencies required for tuning. Oscope to check those signals before I hook them up to the radio ... don't want to fry anything.

Thanks for the help and encouragement.

[Shiny]

Nice! Looks like you had fun and now have a personal treasure.

Thanks for sharing your experience. I like the happy ending with wiggles on your scope. That's a fancy signal generator!

Is that a "sacrificial" speaker for the bench test?

How much current did the radio draw? I remember being surprised.

I'm not an EE but enjoy soldering and these old electronics are much more "hobby friendly" than modern surface mount components.

[Stuart]

Well done. Too bad there isn't much to listen to on AM anymore - back in the old days you could buy FM converters at the parts store, you can still find them at swap meets or online from time to time.

Originally Posted by dataway

Digi-Key is amazing, they have tens of thousands of different components .. they will send you a single resistor if you want it. Every single item has specs, pictures etc.

Before I retired, Digi-Key's Minneapolis office was one floor below me.

[dataway]

I sent back the first signal generator I bought ... it was total garbage from a build quality point of view. Decided if I was going to get one, might as well get a decent one. This one ran a bit over $300.

Yep, that's an 8 ohm speaker I used for testing, two 10 ohms mounted in the car already.

At 13 volts the radio was using a pretty steady 0.9+ amps ... didn't seem to vary much with volume, might be different with two speakers, not sure. I was surprised it used so little for such a large device that does generate a bit of heat.

Oh ... good idea on the FM converter ... I had one of those installed for a while back in the day, might make a nice period addition.

I wonder how long places like Digi-Key and McMaster-Carr will still be around ... excellent US companies that provide excellent service, selling non-Asian products whenever they can.

[Shiny]

Originally Posted by dataway

At 13 volts the radio was using a pretty steady 0.9+ amps ... didn't seem to vary much with volume, might be different with two speakers, not sure. I was surprised it used so little for such a large device that does generate a bit of heat.

That works! I don't remember how much current mine pulled but it overwhelmed my "go-to" power supply and I had to buy a bigger one. Glad you avoided that and were able to buy a nice signal generator instead!

I wonder how long places like Digi-Key and McMaster-Carr will still be around ... excellent US companies that provide excellent service, selling non-Asian products whenever they can.

In my previous life as an employed human, we bought lots of parts from them (and others like them) even though they had nothing to do with parts going into our products. Multiply this by hundreds of thousands of similar organizations and I suspect they have a good future. I sure hope so because as you say, they are amazing when a hobbyist needs a few parts for an old radio.

[dataway]

I can't claim to know why, but the radio and the power supply sure acted as if it was using more than 0.9 amps ... that particular power supply was 3.0 amps and it seemed to be laboring more than I would think. I don't know enough about audio circuits to know if there is something that would cause a false reading on the supply.

[Shiny]

Originally Posted by dataway

I can't claim to know why, but the radio and the power supply sure acted as if it was using more than 0.9 amps ... that particular power supply was 3.0 amps and it seemed to be laboring more than I would think. I don't know enough about audio circuits to know if there is something that would cause a false reading on the supply.

Hope I didn't suggest there was a concern. Was not my intent! Your supply won't lie and an amp at 13V sounds right.

The supply I over-taxed was 1.7A max at 20 V. My AM/FM Stereo was broken when I bought it and may have had a short. The radio may also consume more than yours. All I know is I now own a tank of a DC supply that is unlikely to get used again any time soon.

[dataway]

Excellent ... I was going to ask which radio you were using. I'd bet the AM/FM is higher output than a 68 AM. Power supply I used was 3 amp, 30v. Have a 10 amp, 30v for the shop ... recently used it to power up the dashboard and harness for testing .... even the cigarette lighter worked In the next week or so I'll use it to power up the whole dashboard, engine and AC harness on the bench .... see if it can power the blower motor

PS. Quit smoking about 10 years ago .... seeing the glowing red lighter ... made me feel kind of weird for a moment.

[Shiny]

Serious congrats for quitting smoking. That is a huge accomplishment - hard to do.

I quit in my late thirties so it's way past fresh but I still get tweaked by stuff like your lighter glowing.

My radio is a 71 AM/FM Stereo from a GP. I'll see if I can find the current draw.

It took me many months to get it working:

https://forums.maxperformanceinc.com...errerid=160974

[dataway]

Wow, that unit is considerably more complex than my AM only. Looks to have a larger heat sink, so maybe higher power transistor.

Was it totally dead when you started? I don't think I would have attempted my project if the radio was totally dead unless I found a very obvious culprit on first examination.

My knowledge of IC repair is almost nill ... typical route is replacement unless I have a good pinout and obvious values I can check.

I assume you had the circuit diagram for it?

I find myself wanting to make another one work

[Shiny]

Originally Posted by dataway

Wow, that unit is considerably more complex than my AM only. Looks to have a larger heat sink, so maybe higher power transistor.

Was it totally dead when you started? I don't think I would have attempted my project if the radio was totally dead unless I found a very obvious culprit on first examination.

My knowledge of IC repair is almost nill ... typical route is replacement unless I have a good pinout and obvious values I can check.

I assume you had the circuit diagram for it?

I find myself wanting to make another one work

I think it's cool you took this on and I know you feel good about it! I also understand the draw of repeating the experience.

I started building electronic kits as a kid and half my career was in electronics packaging, assembly processes, and reliability. I know a lot about the parts, soldering, how stuff is made, how it fails, etc. but not much about how it works! I learned a lot from electrical engineers but not enough to debug a radio, let alone AM/FM/Stereo.

I was hoping to clean mine up, replace the electrolytics, and be done. Didn't happen... as I had stepped in WAY over my head as I found the radio was completely dead. There was heat damage under the fusible resistor on one output circuit so as you note, I had a clue, but that proved to be the tip of the iceberg.

That's why it took me so long. I had a lot to learn. I bought a Sam's repair guide and when that wasn't enough, I actually bought an engineering book to understand more about how it worked. I bought a used scope, signal generator, and power supply, only to find the power supply wasn't big enough.

Then the unpleasant realities - germanium power transistors are hard to find. Delco hybrid modules are even harder to find.

Let's just say it kept me busy for several months. Why? I dunno, was just the challenge and a way to learn something.