Vintage GE Alarm clock/ tube radio

[ratdude747]

Picked up my 1st tube radio for $5:



It has issues... so far, I know it doesn't run. It also looks to have been in a barn or arric for some time:



It has some nice features:



From looking at the pcb through the vents, I saw a burnt trace and lots of bad joints... I also saw a datecode sticker that tells me it was made in the 26th week of 1956.

Besides the series light bulb trick, are there any general pointers I should know?

[budm]

Re: Vintage GE Alarm clock/ tube radio

Check ALL the paper caps for short or leakage or just replace them with orange drops cap, if the coupling cap between stage has leakage, it will cause the tube to be bias on badly, you may see the output plate of the final audio output stage turns red hot.
I would use the Variac or lamp to slowly bring up the B+ to reform the DC filter caps but should check for shorts first, also check to see if it has any cap connected between the chassis to either wire of the power cord, be careful and replace that cap with X/Y type using polarized cord, if you touch the chassis and your body is grounded, you may get nasty shock!

[ben7]

Re: Vintage GE Alarm clock/ tube radio

Same as budm said;

Also, it is common for old resistors to change value without ANY physical signs (I.E. black marks, discoloring, crumbling) of being bad.

[ratdude747]

Re: Vintage GE Alarm clock/ tube radio

I'm not swapping the cord since the stock cord is in great shape and I don't want to kill it's antique value.

By orange drop caps what do you mean? I'm new Vacuum tube style electronics and I may need the "noob treatment" at first here.

[ben7]

Re: Vintage GE Alarm clock/ tube radio

By orange drop caps what do you mean?

These

[ratdude747]

Re: Vintage GE Alarm clock/ tube radio

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

[budm]

Re: Vintage GE Alarm clock/ tube radio

And at least do the AC leakage current check for safety in case something inside has insulation breakdown.

[kc8adu]

Re: Vintage GE Alarm clock/ tube radio

the 2 most important are the across the line/line to chassis.the old paper caps will be quite leaky and may go bang.
and as mentioned the coupling cap to the 50c5/50l6 grid.
all paper caps and lytics get replaced here.
shorted lytics will kill the 35w4/35z5 heater.
if the telechron motor is stuck/noisy i have a procedure to save it too.
if this thing has black caps with resistor color code stripes they are bad too.called black beauties we call em black leakies.audiophools want them so dont toss.
you may be able to fund the parts for the restoration by ebaying them!
this is a fine first radio restoration.easy to do and not much to lose if you goof.

[kc8adu]

Re: Vintage GE Alarm clock/ tube radio

dont forget these are "hot chassis"
one side of the ac line is chassis ground.
depending on how its plugged in it could be the hot rather than neutral.touch it and a grounded object and ZAP!!

[twbranch]

Re: Vintage GE Alarm clock/ tube radio

as a tech with experience working on tubed electronics always use a variac to power it up slowly. It could be in perfect condition and the sudden burst of electricity could cause a ton of issues with old equipment. I have two scopes that are tube and they always connected to variac.

[ratdude747]

Re: Vintage GE Alarm clock/ tube radio

What if I don't have a variac?

[ben7]

Re: Vintage GE Alarm clock/ tube radio

What if I don't have a variac?

Make a ghetto variac! with switches, and lightbulbs, to increase the maximum power flow bit by bit. By switching on and off different bulbs (sometimes in combinations together) you can make a basic variac.

A real variac uses a transformer though. But its the same principle, the graphite brush on the variac goes from winding to winding on the variac when you turn the knob. A variac is basically a variable autotransformer.

[gilly1984]

Re: Vintage GE Alarm clock/ tube radio

Can a simple variac be made using a dimmer switch for a light?

http://www.google.co.uk/products/cat...ed=0CE8Q8wIwAg

Could use a DMM to write down the voltages on the faceplate?

Obviously just to be used on low wattage electricals.

Just a thought.

[twbranch]

Re: Vintage GE Alarm clock/ tube radio

All a variac is is two transformers back to back. Probably find plans online to build one. Google it. I would but I am at work and shouldn't be here anyway!

[budm]

Re: Vintage GE Alarm clock/ tube radio

VARIAC is just a TOROID Auto transformer with movable contact so you can adjust the output depends on where the tap is. I used it everyday.
http://www.nmr.mgh.harvard.edu/~reese/VariacPage/

[twbranch]

Re: Vintage GE Alarm clock/ tube radio

VARIAC is just a TOROID Auto transformer with movable contact so you can adjust the output depends on where the tap is. I used it everyday.
http://www.nmr.mgh.harvard.edu/~reese/VariacPage/

Nice link. More than I will ever need to know!

[ratdude747]

Re: Vintage GE Alarm clock/ tube radio

Can a simple variac be made using a dimmer switch for a light?

http://www.google.co.uk/products/cat...ed=0CE8Q8wIwAg

Could use a DMM to write down the voltages on the faceplate?

Obviously just to be used on low wattage electricals.

Just a thought.

I looked it up, they produce sawtooth waves, not sine waves. Not good

Looks like I may have to wait on the project until I can get a used one cheap or the like. I don't think my college has one I have access to.

[ratdude747]

Re: Vintage GE Alarm clock/ tube radio

I opened the beast... and here's some pics:



I had already pulled the tubes, whose postions were included on a paper guide inside the unit:



It's pretty nasty inside:



As shown, there are black beauties inside... I didn't find any paper caps or obvious lytics... maybe I am missing something here.

Another black beauty:



When I opened it, the antenna mount was busted:



I think I can use a 1/2" black plastic cable clamp/mount to replace that...

--

I also restrung the tuner pulley system... the existing string was loose; I added a few knots to get it back to the correct length. However, the varicap is hardish to turn... any way to lube one of those without messing up it's cap range?

It looks like I need to order some mylar caps... how does one translate the color codes on the black beauties (as in where does the range start)?

---

I also built a series lightbulb rig... it has an on-off switch for the output and a switch to switch it between series light bulb and full 120V.

[budm]

Re: Vintage GE Alarm clock/ tube radio

Boy, those are the same set of tubes I used to build my first electronics project when I was 14 years old. I had to save a lot of money to come up with all the parts. Built on a wooden chassis that is lined with aluminum foil.

[delaware74b]

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.