OEM 1940 Radio repair

[Ivan_B]

I've got another noteworthy repair to share. Made my original 1940 Philco C-1708 working again. ?

This was actually inspired by the following comment in another recent thread:

I thought it to be not very informative when the person in the video mentioned that the original tube radio is not repairable or not worth the trouble to repair, and simply gutted the whole thing and put a modern player inside. ? And I thought to myself - this ain't right, I can do better - I can fix the OEM radio. And I did.

 

Here is a short version:

The most common problem in all tube radios seems to be the electrolytic filter condensers, which age and go bad with time. This is most often evident by the buzz/hum sound audible from the speaker when the radio is turned on. This sound has no response to the volume control and it is not to be confused with the buzzing of the electro-mechanical vibrator inside the radio itself. The filter condenser hum is actually coming from the speaker, not the radio.

 

How to fix it? Quite simple - you need to replace the filter condensers, and all the other paper (outdated) condensers you find inside the radio. You can usually keep the resistors, mica (bakelite) condensers, tubes, and other parts, unless they test bad. Some people also prefer to replace the electro-mechanical vibrator with a more modern solid-state one, but I kept the original, since it is working without issues. The condensers you use (called capacitors, or caps, now-days) should be the same as the original ones, in terms of the capacitance and voltage specs. Going up in voltage is okay, if necessary. The capacitance can also deviate within +20% of the original value. This allows you to find cheaper and commonly available replacement components.

 

Here is the list of parts for the C-1708 radio I used:

caps

ECW-HA3C202HQ - 1

ECW-H20402HVB - 2

EEU-EE2V150 - 1

EEU-ED2V100 - 1

DME1P56K-F - 2

DME2S56K-F - 4

103MSR400K - 4

DME4P27K-F - 1

ECA-1EM220 - 1

$24.45

 

2 new knobs (mine deteriorated completely)

1450DR

$16.67

 

1 Philco 7B8 tube (mine turned out to have an open heater circuit)

$4.99 (on eBay)

 

This is it. For a grand total of $46.11 I now have a working OEM radio. Parts delivered to my door.

The repair was performed with a cheap soldering iron kit and a regular digital multi-meter. Also I am a not an electronics specialist, at all. So if some of you with proper education are reading this and thinking that I am full of nonsense - you are right  ?

 

For the long version:

After I replaced the condensers, found a faulty tube, and checked everything else, the radio still would not work. I spent days educating myself in radio repairs, etc., and troubleshooting all kinds of different components. In result, at some point it started working, all of a sudden, and I still don't know what happened. But don't worry, yours is going to be different - a quick and simple repair ?

 

And here are some illustrations, as always:

Original radio and new parts.

 

New parts installed.

 

I really cheated with the buttons. Technically, they are supposed to be semi-transparent, with labels, and illuminated by the pilot lamp from inside. But I had no tools or time to do a more or less proper restoration, so I cut new cores from a plastic base board, embedded the metal connector for the button rod, and used a switch plate for the ivory inserts to match the new knobs.

 

In the end, I think it turned out acceptable, cosmetically. Although, I must admit that if the darker knobs were available, these would look better.

 

The schematics for this radio are available here: http://www.nostalgiaair.org/PagesByModel/952/M0013952.pdf

Edited October 11, 2023 by Ivan_B

[Sniper]

4 minutes ago, Ivan_B said:

1 Philco 7B8 tube (mine turned out to have an open heater circuit)

 

Way back in my sailor days I used to work on a lot of gear that had tubes.  Open heater circuits are the number one failure mode of tubes.  The heaters are always running because the tubes won't work without them, so even if the tube isn't being used the heater is running, so that part fails most commonly.  If it ain't glowing, it's bad, lol.  That is also why tube radios don;t turn on instantly, till the tubes heat up they won't conduct. 

 

Now granted there are tubes out there that you cannot see the heater filaments, but those aren't used in our stuff. 

 

You did good. 

[DonaldSmith]

Jump for joy! 

That's what i did years ago when I got my radio working.  I found an on-lne source for the capcators, and I zapped the vibrator with house current run through a light bulb.  

I love the hum. 

[bacelaw]

I posted the bluetooth device link.  I'm a purist and love that you got your AM radio functional...Mine was beyond repair, with melted wires, and AM radio doesn't provide much content these days.  So, all I did was hook the bluetooth device to the internal speaker, and to the switched power supply - that's it.  So now we can listen to 1940's music via Spotify through our phone (or podcasts, or anything for that matter), and no one knows the original radio was modified...

 

I think it's a balance between keeping things absolutely original versus the benefit and enjoyment we get choosing our soundtrack when out for a ride.  My wife absolutely loves the experience of the 1940's soundtrack as we cruise around.  To each his own...

[Ivan_B]

1 hour ago, bacelaw said:

Mine was beyond repair, with melted wires, and AM radio doesn't provide much content these days.

Do you have any pictures of the insides? Do you still have the insides? These could be useful for parts...

I've seen some pretty bad looking, liquid damaged, sets being repaired without problems. These old radios are very simple and sturdy. In one video I saw, the person was complaining that his friend gave him a radio to fix and it is beyond repair, for like 45 minutes. And then he decided to actually check it, and fixed it by replacing a cap or two, in the next 15 minutes... Very funny ?

 

My next plan is to install an mp3 to AM transmitter, so that I can broadcast my own music from a USB stick. I know there are already things like that available, but I don't like the ones I've seen, so I'll have to make my own. Already found suitable parts for testing, so there will be a separate thread about that.

If everything goes well, I'll be "tubing" down the road with Dolly Dawn, very soon ?

 

Forgot to mention: this radio repair stuff is extremely addictive! This was my very first tube radio (which I had to fix just because I needed a working radio) and I already found myself looking online for cheap broken radios for sale in my spare time... A very slippery slope... ?

[D35 Torpedo]

I'd like to tackle mine. But..I'm lacking a good schematic and am having a hard time identifying the old caps. Maybe I'll give it a second look this winter.

[Ivan_B]

Do it! It is a lot of fun. Technically, you do not need a schematic for cap replacement or very basic troubleshooting. The caps have labels on them

And if you get lost, you can ask for help on the radio forum, like I did.

[soth122003]

I used to do that when the dinosaurs walked the earth. Now with bad eyesight and shaky hands, I'm liable to hurt myself more than the radio.

 

Joe Lee

[GTfastbacker]

i’ll try to go that way. I missplaced my PHD in rocket sience but my NYC taxi driver permit is still valid.

 

So what can go wrong?

 

Thank you for the motivation to do it by myself!

 

Joe

[Ivan_B]

Joe,

 

You'll be just fine! If you run into any trouble, there is also a great radio forum available: https://antiqueradios.com/forums/index.php You can always ask those guys for help, like I did. There is also a specific Philco forum, but it has less users, so I did not write there since my questions were about general troubleshooting and not Philco specific.

 

BTW, I think your 41 radio is technically the next model, although, very similar. Just check your old condenser specs (stamped on the side) before ordering the replacements I have listed above.

 

Also, here are a couple of videos for you:

 

Edited March 14 by Ivan_B

[Plymouthy Adams]

14 hours ago, GTfastbacker said:

i’ll try to go that way. I missplaced my PHD in rocket sience but my NYC taxi driver permit is still valid.

 

So what can go wrong?

 

Thank you for the motivation to do it by myself!

 

Joe

You don't need either of the above, just be sure to spend at least one night at a Holiday Inn.....PS sleeping in their parking lot does not count and renders you totally ineffective.