[David B]

Hi:
Just obtained a Philco 42-380 and was trying it out to see if it worked. Nice radio with great cabinet for restoration. Problem, When I turn it on it just hums, with no change when the volume is adjusted, or tuned to another station or band.

I pulled all the tubes and tested same, most were OK. A few were in the questionable range, the two 42s and one of the 7B7 tubes.

It seems like perhaps a bad capacitor, or capacitors, especially with no change when the volume control is sdjusted, just the same loud hum.

Two questions in light of the fact I am a novice:

1. What do you think is wrong and what should I try first?

2. Do you know of a good trouble shooting book for these radios that describes various problems and what to look for and and how to repair the problem?

Thanks much for the help,


God bless one and all,

Dave B

[mandh]

My guess would be that the power supply electrolytics are gone. The very first thing to do with any old radio is to replace these capacitors to prevent damage to the radio's power transformer and to get the hum issue out of the way. When the caps are bad you are putting pulsating DC out on the power supply lines, thus the hum.

[David B]

Harv:

In that I am a newbie, which of the electrolytic capacitors are for the the power supply. I have the schematic, could you give me the values or part number. I noted that perhaps two of the electrolytic's were replaced at some prior point in that there are two big new ones under the chase, but I don't know which ones. So any advice you could offer is greatly appreciated. Further, I plan to order a cap kit for the radio and replace them all, Again thanks .

God bless,

Dave

[Texasrocker]

Hello David B, Welcome! I took a quick look at the JF Riders schematic for the Philco mod 42-380 parts list.
It shows that the set originally had 2 electrolytic condensers mounted in one unit. IE: 2 separate leads from 1 electrolytic can chassis-mount type
condenser. Negative polarity of orig electrolytics is most probably the orig tubular can (if still mounted to chassis, to chassis ground itself?). If someone replaced the electrolytics before under chassis, you will probably see 2 separate larger-size old cardboard type tubular replacements with a ( +) end on them both.
The JF Riders schematic shows both orig Philco electrolytic condensers for your set were the same value in ufs, and same voltage rating. IE: 2 electrolytic condensers rated at 8uf @ 475 volts.
Good modern day subs would be: (2) individual 10ufs@500 volts electrolytics types replacement condensers. Closely observe polarity +/- on the old caps installed, and if both (-) ends go to chassis ground, sub in the new (+) ends from each electrolytic to their respective solder locations (+) ends of the old electrolytics caps installed now, twist together both the negative leads, (follow printed arrows) for neg ends of both new caps, and solder them to chassis. Remove the old electrolytic caps one at a time by subbing-in the new ones. Unless your chassis has a "floating isolated ground for the new caps (-) side, you should be "hum-free", and safe to bring the set back to life. Check a schematic first for free at: http://www.nostalgiaair.org .
Good luck restoring your Philco!!

[David B]

Tex:

Thank you, good advice, I will replace the new old electrolytics units under the chase as well as the other caps and see what we get.

God bless and have a great day,


Dave B

[Ron Ramirez]

Hi Dave

Be aware that there are THREE electrolytics in the 42-380.

Two were originally contained in one cardboard tube; the other in its own cardboard tube. Both were mounted together against the chassis (not chase - you work on a chassis; you chase your wife ).

Part (20) contains two 8 uF, 475 volt units, part (61) is a single 18 uF, 475 volt unit.

Neither 8 uF, 18 uF, nor a 475 volt rating are standard anymore. Today, 10 uF is generally used to replace 8 uF, and 22 uF replaces 18 uF.

Normally, you would need to go to 500 VDC rating to replace an old 475 volt condenser. However, please note that on this model, the voltage rating are greatly over-rated; condenser (20A), part of (20), will only "see" around 200 volts (original measurement 195V, I'm allowing for today's higher line voltage and more sensitive multimeters). (20) is only getting around 90V, and (61), probably in the neighborhood of 250 to 300 volts.

Therefore, for these particular parts, you may safely use 450 volt replacement electrolytics, since 500 volt electrolytics are sometimes harder to find, and not needed in this application.

But until you become more well versed in electronics, please do not ever assume you may replace an electrolytic with one rated at a lower voltage - most of the time, you can't. This, however, is one of those occasional instances where you can.

Speaking of learning. Never, ever, plug in and turn on an old radio until it has been checked out for signs of trouble. This includes, but is not limited to, replacing the electrolytics right away before going any further. They are almost always bad, or in the process of going bad. (This is what makes the set hum - the electrolytics are no longer doing their job of filtering the set's high voltage power. In other words, they have failed, and could short at any time.)

Failure to heed this warning could result in one or more of the electrolytics shorting out, taking your set's power transformer with it.

And please understand, I am not trying to criticize you, but merely trying to help and educate you at the same time. This is a great hobby. But safety must be observed, and part of that is to never plug in that radio you just bought without, at the very least, replacing those electrolytics.

[David B]

Ron and All Concerned,

I greatly appreciate all your input, including any and all criticisms for they are well intended and towards a good reason. I checked the unit before plugging it in and it appeared to be OK. My first indication that there was a problem was the hum. I now know that humming radios mean potentially serious problems which needs to be dealt with immediately. My first order of business is to order a cap kit and replace most if not all the caps including the electrolytic. Indeed this is a great hobby and you meet alot of interesting and very intelligent people who have spent a lifetime restoring these wonders of yesteryear. You also meet some great people like you Ron, who help people out of jams such as a speaker on a previous restoration, again thank you. In the future I will not allow the radio to hum rather fix it until it does know the words and sounds them out clearly. Further, I will check under the chassis for other problems and chase my wife again in a couple of days. God bless you one and all, your always there when needed.


Dave B.