[BenWA]

if you don't have variac use dim bulb set up

You're going to have to expand on that thought. I am a complete newbie to this stuff.


I saw a picture someplace online where someone clamped blocks of wood to either side of the chassis so they can have it turned upside down on their workbench which looked like a great way to keep it turned that way for working on.

This is the workbench I have my eye on, but I'd have to get a piece of wood cut for the top to cover the metal. For my small apartment, I think that size would be ideal.
http://www.harborfreight.com/multipurpos...60723.html

I wear strong prescription glasses so I won't think a wearable magnifying glass would work well for me. These would be ideal though:

Unlit: http://www.harborfreight.com/helping-hands-60501.html
Lighted: http://www.harborfreight.com/jumbo-helpi...65779.html

Heat guns, at least harbor Freight ones, don't last worth a darn. I had 2 of them. The first one died after a week and I got 1 free replacement. The second one lasted longer but then quit also. I was using it for heat shrink tubing on just wire splices, no components involved. I turned to using a grill lighter after that which worked great. Obviously, a grill lighter wouldn't be good for this task, but a hair dryer might work nicely and they don't burn out as fast as heat guns. Plus you can pick them up used for a few dollars if they do wear out.

[PAradiogeek]

Ben,

Regarding dim bulb testing, here is a great page: http://www.antiqueradio.org/dimbulb.htm

I have just read through the entire thread. You seem to be of the opinion that vacuum tubes are the weak link in an old radio. That is simply not the case. Tubes are actually quite reliable compared to other components, especially electrolytic and paper capacitors. This is not to say that they never fail, just that those other components are _much_ more likely to fail. That is why they should get replaced first.

At this point you know that there is a fault somewhere in the radio, because the power transformer is overheating when the unit is powered. I recommend that you replace ALL of the paper and electrolytic caps before you power the unit again.
Jon

[BenWA]

Thanks for the helpful link. I will build one of those soon.

I had the 7Y4 tube tested by someone with a proper tester... and it is bad in every way possible. Just like my multimeter showed, it was shorted out across ALL operable pins. (1, 3, 6, 7, 8). It was completely fried. That is more likely the problem. It was just a 73 year old tube (Philco brand! probably original!) that finally bit the dust.

All the rest of the tubes are tested good, although the two 7B7 tubes are weak (in the "?" area on his tester) and could go out next.

He had a Zenith brand 7A4 for $2.75 so I got it. It tested good on the same tube tester right after mine tested bad.

I am going to replace the speaker wires at the very least before I power it up again. The insulation is almost entirely gone in sections. That can't be healthy for it.

All the paper caps have already been replaced. Are these the electrolytic caps? (The ones circled in the attached pic)

EDIT: The round one you see in the back IS an old Zenith electrolytic capacitor... BUT upon further inspection, it's no longer connected to anything. Makes sense since there are large capacitors right under it (when the chassis is sitting upright) so it has been bypassed with modern caps, but left intact for appearances, I guess.

[Warren]

You have to remember that something else in the radio could have ruined the tube. After all it worked at first. Like PARadiogeek suggested you should replace all components and bad wiring before powering up again, if not you might be looking for a new transformer soon if not more. The dim light bilb/variac is essential, but everything needs to be repaired as well as you can even before using it.

[BenWA]

Yes, it's possible something else could have damaged it, but it's questionable. It may have been a 73 year old vacuum tube that finally went south. It's a Philco tube, probably original. (Also not a rare or expensive tube, so no major loss). I powered it up a good many times and it always worked. Then suddenly it went bad. The tube died when I tried to power it up again, not in the middle of use.

I am going to see about replacing things that are obviously bad before I power it up again.

However, replacing new modern capacitors just for the sake of doing so would be really wasteful and pointless unless there is a pattern of the same tube blowing out. We're talking about a vacuum tube that may have been 73 years old when it went out.

If after I replace the bad wires and it blows the same tube quickly, then I'll know something else is wrong. In the meantime, I will stick the chassis back in and leave it until I get new wires for the speakers and other things. I will also build and utilize a bulb tester thing. I also want to add a fuse for the transformer to protect it in general.

Also, the fellow who tested the tubes for me said that when I laid the chassis on it's side AFTER I smelled burning, unplugged it and pull it out of the cabinet (when the tube went bad), that it may have caused further shorting in the tube from loose filament inside which is why it went even worse with the blue sparking I witness. (Note to self, don't power up vac tubes on their sides)

So all signs point to that one bad tube. You have to start small and troubleshoot things. If your car stalls on the side of the road, you don't just decide to rebuild the entire engine right then and there. I suppose you could.. but why if nothing is wrong except the fuel filter?

Since the chassis has already been retrofitted with modern capacitors, there's little reason to suspect a problem there at this particular moment. It was operating fine with good audio, no strange sounds and no burning smell until this one vacuum tube went bad.

[mikethedruid]

The two rectangular cans at the front of the picture are NOT capacitors, but most likely IF transformers. The round thing circled in the back looks like a filter cap. Before you get in much deeper, get some books on old radio, and find what various parts looked like in the 1930s and 40s. It will save you time and trouble in the end.

[BenWA]

The two rectangular cans at the front of the picture are NOT capacitors, but most likely IF transformers. The round thing circled in the back looks like a filter cap. Before you get in much deeper, get some books on old radio, and find what various parts looked like in the 1930s and 40s. It will save you time and trouble in the end.

Yes, I intended to. I reserved 2 books through the library's online system last night. I just returned from picking those 2 up -- plus 1 more on the subject of antique radio restoration. plus 2 on reading schematics. So I have lots of reference material for now. Depending which books I like, I may order used copies online. They are nice general reference guides.

[Warren]

If your car stalls on the side of the road, you don't just decide to rebuild the entire engine right then and there. I suppose you could.. but why if nothing is wrong except the fuel filter?

Your car didn't start smoking either if it only needed a fuel filter. Also, repairing a car vs an old radio is like comparing apples to oranges but,

OK, Up to you if you wanna take a chance on ruining the transformer and what ever else.. But, Good Luck.

[BenWA]

Warren, you are purposely trying to be rude -- and it's completely uncalled for.

Shall I point out how many times in this thread I said I am going to take every precaution possible including putting a fuse to protect the transformer?

PAradiogeek did not say to replace "everything". The exact quote was:

I recommend that you replace ALL of the paper and electrolytic caps before you power the unit again.

Since there are no paper and electrolytic caps in it, there is nothing to replace, except the bad wires which I have already said I am going to do.

The rectifier tube was 50-73 years old. It went bad. It's completely shorted out. It happens. It's the nature of the beast. They do wear out.

[Warren]

No, I didn't mean to replace "everything", i'm sorry you misunderstood me. Would seem if you replaced eveything you would just be building a new radio . Also I am not trying to be rude, just wanted to make a point to you. I was hoping my smiley face at the end would let you know I am trying to be friendly just making a point. I was sincere when I said Good Luck on it. No hard feelings I hope.

[sam]

ben
I don`t think he`s trying being rude just lot of people come in asking same questions and some don`t listen
very least get a schematic and recheck all caps including electrolytic`s
philco`s rubber wiring is bad it crumble's when touched
it is your radio so you can do what ever you want put new tube in test it`s up to you
sam

[Ron Ramirez]

I figured out to unplug the speaker cable (it's in HORRIBLE shape with bare wire showing! I need to redo that ASAP!)

Yes, you do. Do not attempt to apply power to that radio again until you have replaced the speaker wiring harness, and any other frayed/substandard wire. This could possibly have caused your 7Y4 to go bad.

Now...

As far as rudeness, if any of us on the mod team see any of that going on, we will blow the whistle on it. It isn't allowed per Phorum rules. As Sam said (and I concur), I don't think Warren was purposely trying to be rude. Warren even said he was sorry if you misunderstood him. We're all only trying to help.

OK, boys, carry on...

[BenWA]

I think the misunderstanding was on his end ... but anyhow.

Yes, I am sure a lot of completely clueless people do show up and have no interest in actually learning proper repair and just expect a magic band aid to fix their machines.

Funny I should say it that way. There is what appears to be a piece of thick type of medical tape on top of that one old Zenith electrolytic cap to insulate it from the loose dial indicator panel which is loose due to rotten rubber mounts. But hey, at least someone tried to keep things from shorting out! I wonder if the rotten rubber allowing the mounting bolts to contact chassis frame could also be a problem with it. I will post pics of what I am referring to later on tonight or tomorrow.

[exray]

But hey, at least someone tried to keep things from shorting out! I wonder if the rotten rubber allowing the mounting bolts to contact chassis frame could also be a problem with it.

Have you not done perfunctory cap replacement yet?
As an old sage once told me..."trying to troubleshoot an old radio with old caps is like trying to light a fire with wet matches.

[BenWA]

Have you not done perfunctory cap replacement yet?

The what?


I went ahead and took the pic now. The yellow circles show the bolts that hold in the radio dial face and button assembly.

There are supposed to be rubber mounts on both sides that seem to isolate the bolt and the upper assembly from the lower portion of the chassis. Maybe for an electrical reason. I did notice a piece of rotten rubber, about the size of those, fall out yesterday. I can't remember if that was before or after it blew the tube. I'm going to check at a hardware store for some kind of rubber washers to stick in there on both sides to restore that also before it gets plugged in again.

The green circle shows the bandage tape I mentioned.

[Image: http://img.photobucket.com/albums/v222/i...mounts.jpg]