Vintage GE Alarm clock/ tube radio

[ratdude747]

Re: Vintage GE Alarm clock/ tube radio

RD - the electrolytic cap is the large round bare metal can, seen from your first and third photos in post #18.

It looks like a combo 75 and 30uF cap.

Noted.

[twbranch]

Re: Vintage GE Alarm clock/ tube radio

Clean it up and you may have a nice radio. I have seen worse!

[ratdude747]

Re: Vintage GE Alarm clock/ tube radio

Ordered the caps (I had some other crap to get and lumped the shipping).

Question: I found a Black plastic radial Lytic (labeled .047 MFD)... Is the side with the text the + or the - ?

[ben7]

Re: Vintage GE Alarm clock/ tube radio

Ordered the caps (I had some other crap to get and lumped the shipping).

Question: I found a Black plastic radial Lytic (labeled .047 MFD)... Is the side with the text the + or the - ?

Picture?

Are you sure its not a film cap?

If it doesn't show any plus or minus, then it must either be a non-polar electrolytic, or a film capacitor.

[ratdude747]

Re: Vintage GE Alarm clock/ tube radio

Picture?

Are you sure its not a film cap?

If it doesn't show any plus or minus, then it must either be a non-polar electrolytic, or a film capacitor.

It was pyramid brand... I think I saw a dash on the text side but I frankly couldn't tell (it was worn off). It was mounted right by the variable capacitor (To read the printed specs, I had to desolder it).

[kaboom]

Re: Vintage GE Alarm clock/ tube radio

It was pyramid brand... I think I saw a dash on the text side but I frankly couldn't tell (it was worn off). It was mounted right by the variable capacitor (To read the printed specs, I had to desolder it).

Between the capacitor frame and chassis?

It's a paper cap. The outer foil was marked with a "-" on those. This would sometimes be used to shield a Hi-Z ckt by having the outer foil grounded or at some low impedance, and the "inner foil" was the signal or whatever.

But they were not polarized.

It might be a paper-in-oil cap, but those were/are more likely to be found in "more sophisticated"/more expensive equipment such as HiFi tone controls, etc.

-Paul

[Hemingray]

Re: Vintage GE Alarm clock/ tube radio

Be sure to replace the 75/30uF cap with caps rated to at least 105*C. Unlike a motherboard or PSU, you can use general caps here. You will have to use modern values for these:

30uF/150V = 33uF/160V
75uF/150V = 82uF/160V (you can also use 100uF/160V if you have one)

If you have access to a tube tester, give your tubes a test. the 50C5 is the most likely to have leakage. (hint: if after a total recap you get a low level hum, the 50C5 most likely has "Heater-Cathode" leakage.)

Your radio also uses the smaller IF transformers, IFs from this time frame use silver mica capacitors, and tend to suffer from a symptom called "Silver Mica Disease". Symptoms of this are loud static crashes (like lightning interference) across the dial. This is usually repairable by cutting out the silver mica wafers in the transformer, and tacking on similar valued caps under the chassis on the tx legs. (around 100pF or so)

Your radio also has what are known as "Couplates" (the multi legged brown flat components that look like caps). These actually contain a network of resistors and capacitors. These rarely ever go bad, but in the event you do get a bad one, they can be fabricated using perfboard and modern components.

Tube layout on yours is a slightly odd duck, It's an "AA5" (All American 5), but with a 12AU6 in place of the more commonly used 12BA6. First time I've seen that done, unless maybe at the time this radio was made, GE had a massive batch of 12AU6s handy? (both are essentially the same tube, usually the AU6 is found in FM service)


Good luck!

[bluto]

Re: Vintage GE Alarm clock/ tube radio

If you don't have a tube tester and the set appears dead, then you likely have a tube with a burned out heater (basically a light bulb filament that gives the tubes their glow). When I did my old radio I quickly determined that these are all in series. So when one goes, the whole thing goes dark. Since I didn't have a tube tester, I had to look at the schematic to determine which two pins were for the heater and then check each tube for open circuit. Granted there could be other issues with the tubes that are causing problems. In my case, I did find one bad one and replacing it brought the set back to life. Of course I did a full re-cap also.

[ratdude747]

Re: Vintage GE Alarm clock/ tube radio

I haven't powered it on. I won't until I recap it, and when I do, my university lab has a few variacs that they will let me use to power it on for the first time. Until then, I have no idea what does and doesn't work.

Noted on the one cap being non-polarized. I'll replace it with one of the spare 600V mylar caps of the same value.

The lytics are IIRC 105C. I bought the same values you suggested, 33uf and 82uf.

I don't have tube tester access...

I saw the Couplate on the board... I figured it was some sort of capacitor network or the like.

[Hemingray]

Re: Vintage GE Alarm clock/ tube radio

Shouldn't be too hard to find a tester for a decent price, I use a Sencore TC142 "Mighty Mite" for everything. (Tests everything except the 4/5/6 pin tubes)

I'd say after the recap, give er power, there's no power transformer to risk frying in this one.


Wait till you score a 30s/40s console radio, then the "fun" really begins

[ratdude747]

Re: Vintage GE Alarm clock/ tube radio

Got the solder work done.

I'll power it up on monday when I have variac access.

In the mean time... the Variable Capacitor is kinda sticky. What is the safest thing to use to lubricate it? (w/o messing up the dielectric properties of it)

[Hemingray]

Re: Vintage GE Alarm clock/ tube radio

A slight bit of grease on each end may help.

[ratdude747]

Re: Vintage GE Alarm clock/ tube radio

A slight bit of grease on each end may help.

Noted, I may try some ATF.

Also of note: After looking at the PCB, I was able to figure out which tube pins were heater pins... and I checked for any opens... with the tubes in, there were none. Just enough reisistance to tell me its not shorted but not a lot.

[Krankshaft]

Re: Vintage GE Alarm clock/ tube radio

Ah, mylar film caps. I'm used to them being a dark red...

Orange drop caps aren't mylar they're polypropylene just fyi.

[ben7]

Re: Vintage GE Alarm clock/ tube radio

Orange drop caps aren't mylar they're polypropylene just fyi.

lol

I always just call them film caps, to avoid looking stupid

Ratdude: A google search reveals you can use a light oil, such as sewing machine oil, in the ball bearings of the tuning capacitor. Be careful to not bend the capacitors' plates! Have a look at this

[ratdude747]

Re: Vintage GE Alarm clock/ tube radio

Orange drop caps aren't mylar they're polypropylene just fyi.

Wait... I did use red mylar film caps. Was that a mistake?

[ben7]

Re: Vintage GE Alarm clock/ tube radio

Wait... I did use red mylar film caps. Was that a mistake?

I don't see why it would be a issue.

Only audiophools would say so. They say that the orange-drop capacitors have the best sound.

[ratdude747]

Re: Vintage GE Alarm clock/ tube radio

I don't see why it would be a issue.

Only audiophools would say so. They say that the orange-drop capacitors have the best sound.

ok, they shall stay. I'll borrow a variac between classes monday morning to power it for the first time.

[kc8adu]

Re: Vintage GE Alarm clock/ tube radio

ok, they shall stay. I'll borrow a variac between classes monday morning to power it for the first time.

why?
all the caps are new now.
first test with a dimbulb if it makes you feel better.double check your work and fire it up.worst case you got the 2 filter caps in backwards.
watch the 35z5/35w4 as it warms up.
if it gets suddenly bright pull the plug you have a b+ short.

[kc8adu]

Re: Vintage GE Alarm clock/ tube radio

most common is the 12be6.

Tube layout on yours is a slightly odd duck, It's an "AA5" (All American 5), but with a 12AU6 in place of the more commonly used 12BA6. First time I've seen that done, unless maybe at the time this radio was made, GE had a massive batch of 12AU6s handy? (both are essentially the same tube, usually the AU6 is found in FM service)


Good luck!