Restoration of Philco 38-40T Radio

[Bob Cuthbert]

This will be my 2nd tube radio restoration. My first was a Marconi AC/DC 5 tube AM only radio. Recapped and refinished the wood case and it works great.

This next one will be interesting, it has a plug that allows for 115 AC or 5 Volt DC, some call it a “Farm and Country” radio. It is a 2 band, AM and SW. It is in very good original condition but will need recapped, new cord etc. I used my dim bulb tester when I first powered it up. Everything seems ok, except the dial bulb goes out after the set warms up, or after about 3-4 minutes. I turn the set off, and after it cools down, I turn it back on the and the dial bulb comes back on but again goes out after 3-4 minutes. I have not done anything yet, but I have requested a schematics. I am curious why the dial bulb goes out, (it does not burn out) after the set warms up, short somewhere?. Any quick explanations would be appreciated. Note, I will be removing the chassis and cleaning and recapping and testing the resistors. I don’t have a tube tester but I am going on the assumptions that the radio works so tubes are ok.

thanks

Bob Cuthbert

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[Bob Cuthbert]

Hmmm, second photo did not upload, try again.

Bob

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[Jean Marcotte]

Hi, Bob.

Very special radio you have there. It’s the first time I see a table radio with both AC and 6V DC vibrator power supply. I can see that when operating on DC, the filaments are fed directly from the 6V battery and the B+ comes from a standard vibrator power supply. Now when operating from AC, a primary winding added to the transformer (27 ohms winding) makes it act as a standard power transformer for the B+. But you need 6V to feed the filaments. That is taken out from the windings on the vibrator side of the transformer. The poor quality of the schematic on Nostagia Air makes it difficult to analyse the wiring, especially around the plug at the lower left side. My guess is that something in that area, may the vibrator itself, is cutting filament power after a few minutes of heating and leaves you with a dead radio. Try the radio cold without the vibrator. If it does not come on at all, you have a cle to the problem.

Best regards.

Jean

Attachments:

1. M0013251.pdf

[Bob Cuthbert]

Thanks Jean, the radio works without any 6V DC battery hooked up, the only issue right now is the dial bulb goes out after a couple of minutes upon start up, but the radio continues to work. If I turn the radio off and wait a bit and then turn it back on the dial bulb works so it is not burning out just shutting off. Anyways, I still have to do a primary look after I remove the chassis and make sure there are no shorts and clean tube pins etc. Thanks for the schematics and will keep you posted on how it goes with the restore.

Thanks again

Bob

[Jean Marcotte]

Sorry Bob,

I misread your message. I thought your “dim bulb” was the one going out after a few minutes. Now for the dial lamp, clean all contacts, check all the solder joints and of course try another bulb. What else could it be ?

Jean

[Bob Cuthbert]

No problem Jean, I took out the chassis today and it has about 60 years of dust and cobwebs. I had a hard time getting the little dial bulb out. When I got it out, the filament broke, likely it was almost a goner and that lead it to going out once it got hot. So now I am putting together a list of capacitors and will need a new bulb. I have looked at USA sites for replacement bulbs but their shipping costs are crazy expensive.

The bulb is a bayonet type Philco 47 Holland, 6.3 Volt .15 amps, any one know where to get these in Canada? I live in Prince Rupert BC so finding a electronics store is about 9 hr drive away. Here is a picture.

Thanks

Bob

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[John Greenland]

Bob;

Type 47 bulbs are a very commonly used indicator lamp in all sorts of electronic equipment.
Any electrical or marine supply company should carry them.

Acklands Grainger for one, is showing them.

Good luck

John G. VO1 CAT

[Bob Cuthbert]

Thanks John, we have an Acklands Grainger here in Prince Rupert. I’ll go on the hunt today, but our town is pretty small and little things like a bulb can be hard to find.

Bob

[Bob Cuthbert]

The closest bulb I can find in town is a 4.3 volt 0.75 A bulb. Would this work?

Bob

[Greg Bilodeau]

If the bulb lights and then goes out I would say the bulb is ok, there is some other problem. Can you provide a model number so we can have a look at a schematic and see how the voltage is developed for the bulb. Another thing is the Philco dial light sockets are well known for having an internal short and have to be rebuilt which is an easy process.

Gregb

[Bob Cuthbert]

Hi Greg, the model number is 38-40T, on the schematic. I did see a repair on the bulb holder on the internet. The rubber at the bottom of the socket is rock hard and crumbly. You may be right in that there is a short in the socket, rebuild in order. Thanks for you help. I never did find any #47 6.3 V bulbs in our small town, but Amazon had them so on order.

Bob

Attachments:

1. schematic-38-40.pdf

[Greg Bilodeau]

Hi Bob:
I had a look at the schematic and nothing special about the pilot lamp voltage so will bet its a short in the lamp socket due to the aging of the rubber insulator. Rebuild the socket and that should fix the problem.

Gregb

[Bob Cuthbert]

Thanks for checking, no back ground in electronics so reading the schematics is a new learning experience.

Bob

[Greg Bilodeau]

Do you have a local mentor you could work with? That would be a big help to get you going.

Gregb

[Bob Cuthbert]

Hi Greg, no mentor locally. This radio looks a little more complicated than the AC/DC 5 Tube Marconi I did a recap and cord replacement on so will be needing help.

Here is my extent of experience:

I have a read a fair amount and get the basics but when it comes to testing resistors and checking the tubes I’m over my head. I think I got lucky with the Marconi Model 180 as it was unmolested from 1948. It did not work and with just the changing of the electrolytic capacitors it worked again just fine. I did however replaced all the other paper caps.

I also fix old mechanical clocks and telephones so have some experience.

Interesting to note that the BC Lower mainland Chapter meets at Charles Rummel Park, I lived just down the street and know the area well, but that was over 40 years ago.

If someone on this forum is willing, yes I would be interested in a mentor. I lived in Prince Rupert BC for the past 22 years but don’t know anyone that collects and works on old radios.

Bob

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