Repairing and Restoring Tube Radios - part 3

This is for the electronics geeks out there. I am repairing and restoring an old Marconi model 220 tube radio and I thought I would make kind of a do-it-yourself documentary to share my little hobby with everyone. In part 3, we do a little electronics theory as we learn about rectifiers and filter capacitors, then we replace several capacitors and listen to the cleaned up sound.

Category:

Howto & Style

Tags:

• radio
• tube
• electronics
• capacitor
• repair
• marconi

[musicman0150]

What a nice sound that radio has with that big speaker. Maybe you can answer some questions for me. Can that type of speaker work with a modern radio and can you connect a modern speaker to this type of radio? If so, how is it done? Also, it looked like the speaker cone had some holes in it, or was it just the lighting? Where is the danger spot on that type of speaker when the radio is in operation because it amazes me how electricty flows through and there's no electric buzz at all.

[aliendaddy32]

These older radio speakers actually don't have electricity flowing through the speaker cone. They do have a large (and heavy) magnet in behind the paper cone which converts the electrical energy to mechanical energy which vibrates the speaker. These old speakers actually require a very high voltage that would not be compatible with modern electronics without modifications. There was actually a serious buzz on this radio until I replaced the capacitors.

[biggestdigger]

Great series!

This is the first time I've heard only replacing the bad capacitors. Most just replace all the old C's.

That lightbulb test in the previous lesson was excellent. Is a 60 watt bulb always correct?

Thanks much.

[aliendaddy32]

No, a 60 watt bulb isn't always correct. It should be about the same power as your radio uses to work properly. Go back to about 3:50 in video #2 for a way to guesstimate what bulb you need.

[Quaaludedude714]

good for you :) QC

[vamtim]

Brilliant videos. I'm in the process of restoring a GEC 5645 it's my first attempt at such a restoration. I have to replace all the waxies and electrolytics just waiting for them in the post. Thanks for posting these videos they're immensely helpful.

[bandet888]

In my other comment I ment rectifier CAPACITORS

[bandet888]

Only the rectifier is responsible for any hum noise. How ever most other capacitors are coupling capacitors. It's important to replace these too especialy the paper ones. What happens is they get leaky a lot and through the voltage off the circuit. What ends up happening is when they through the voltage off the amplifier will become distorted. They wont have a DEAD short (you still get a high voltage reading on 1 side) and will test good on a cap checker. Replace them anyway!

[Teflon65]

Some folks take a digital photo of the chassis and wiring and so on, to aid with their memory. You probably know this, but it seems easier than labeling. Also, why is the hum called a 60 cycle hum? I know that bad electrolytics can cause that hum, and that it can ruin the transformer. I'm just unsure about the nomenclature. No expert here, just watching videos like yours and enjoying them tremendously.

[force311999]

@biggestdigger he probably did but tests in between of coarse you replace them all he ordered them all and the rest will go bad very soon after using the set after so long

[force311999]

@greasebird the two caps are of different value the old one has two taps on it so it is like two caps together in one case

[force311999]

@IstvanN1961 the large cap has two caps in it

[greasebird]

It looks like you replaced one big Capacitor with two small capacitors in series. Shouldn't they be in parallel?