[jerryhawthorne]

Jon, there is a use for the dim bulb but not for that. Just replace e-caps, they are cheap.
Jerry

[PAradiogeek]

Thanks Jerry.

[PAradiogeek]

What have I gotten myself into? I've replaced two of the bakelite blocks and things were going swimmingly. Then I decided to alter course a little and now I'm not sure how to proceed. The schematic for this radio shows a capacitor 'item' 7 that is composed of five different capacitors, items 7A through 7E. These capacitors are all placed inside a metal box (shield?) and each of the caps has one end tied to chassis. After getting all full of myself after my second bakelite block replacement, I decided to tackle this beast.

I unscrewed the shield from the chassis, bent back the tabs, and removed the caps from the box. They were wrapped in paper and when I pried apart the paper, I saw this:

http://www.flickr.com/photos/104710683@N04/11459036793/

The caps all seem to be potted together with the same wax used in bakelite blocks. I honestly thought I would find 5 caps soldered neatly to a terminal block (naive?).

So the question is: How do you experts handle a mess like this? The caps, and even the connected wires are all 'glued' together. Should I simply unsolder each wire from it's other end, toss out the whole mess, then install new caps and then string new wires? Some other plan of attack?

Also, is the box important to the circuit? I.e. is it in fact a shield, or just a method of grounding one side of each cap?

Thanks,
Jon

[klondike98]

Jon,
About 17 and a half minutes into this YouTube video, Bob Andersen recaps a very similar box capacitor in his Philco 60MB restoration ... hope that helps
http://www.youtube.com/watch?v=d4hno5fmQuE

[Bradley Rush]

THx klondike98

Video also shows how to finish a cabinet and deal with some problems with that as well.

Bradley

[PAradiogeek]

Perfect, thanks.

Jon

[jerryhawthorne]

Just my approach on those pesky cans in Philcos.
Jerry

getting it out with a bolt and using it as a slide hammer. Nice to have the cardboard cover as it keeps things from sticking.

[Image: http://i303.photobucket.com/albums/nn129...0004-6.jpg]

Jerry

[PAradiogeek]

Ok, another day, another question.

One of the bakelite blocks (item 8 ) in this radio contains two caps with values of .09 uF and 700 uuF. There is another block, item 26, that contains two 110 uuF caps. With other radios I've worked on, capacitors in this range would be mica caps. From what I've read and from my modest experience these caps tend to be pretty stable and don't require replacement. I haven't changed any of them in my other radios and all of the radios have worked after restoration.

Additionally, regarding item 8, the 700 uuF cap is in the oscillator and I presume it is probably a precision cap and couldn't just be replaced by any 20%-accurate cap. So what I did was disconnect the wires to the terminal that has the .09uF cap and wired in a .1 uF cap external to the bakelite block. I left the 700 uuF cap circuitry untouched.

So the question de jour is: Are these low-value caps mica caps that can just be left alone? Does my strategy for dealing with the item 8 block make sense?

Thanks and merry Christmas.
Jon

[Ron Ramirez]

Generally speaking, no, they are not. Most of the low-value caps in these blocks are actually paper, not mica. I have seen a few dual 110 pF blocks that had mica caps in them, but in my experience, the vast majority of those I have replaced have been paper. So you really should replace these as well.

680 pF is the closest standard value for 700 pF, and will work in this circuit with no ill effects. You can replace 110 pF with 100 pF.

[morzh]

Well, as far as I remember a discussion here, those caps in backelite blocks are not micas and are usual papers.
You can easily verify that by measuring the capacitance of that 700pF cap; if you see it gone significantly it is not then a mica as micas stay put. I have just measured three micas in my 90.....if it says 110pF - it is in fact 110pF, and 330pF is 332pF or so.

Now as to the precision, this particular cap though it is in the oscillator is not frequency-defining cap, it is simply a DC feedback bypass cap and so it does not have to be any special type.

[morzh]

Wow....what a sync!

[PAradiogeek]

Ron, Morzh,

Thanks for the information. Now I have to order some caps

Jon

[morzh]

Why the long face! I always feel like when I order caps.

[PAradiogeek]

Morzh,

Well, the long face is really due to the fact that I will now have to wait the better part of a week to get these ordered and back to me. I feel like there is always something I need that I don't have. I'm slowly building up a supply, but I guess it takes time. I've been staring at the radio for the last couple of hours and I know that there are other areas I can work on, but in my simple mind I want to finish one area first, and then move on to the next.

This brings me to another question: I was looking at caps online just now and I see some 680 pF caps, but they are only rated at 50V. Would that voltage rating be sufficient for this "DC feedback bypass cap" in the oscillator section?

Thanks,
Jon

[tab10672]

I know your not supposed to use them, but I replaced the same 3 low value caps in my 89 with high volt ceramic disks and it works great. Todd