My first Silvertone

[jeyurkon]

Originally Posted by charokeeroad

Thanks Chris. I'd like to take one more shot at identifying this cap. It doesn't have any color dots on it that I can make out. It's Solar and from what I've read on Phil's website it should come out right? Is it a paper cap wraped in plastic? I can't repost the picture but it's the same one as shown in entry #49.

The dots would be painted on where you see those circles. They could have been cleaned off. I assume you checked both sides.

Now that you've identified the cap what does the parts list say about it? It should tell you whether it's paper or mica.

[charokeeroad]

Hi jeyurkon, My parts list is shown in entry #28, page 2 of this thread (can't show it again here). It's cap #66. If the parts list is tells me what kind of cap it is I'm missing it. The back side has two dot circles but no color. Stamped into the cap is says what looks like "c100". I do see in the listing for the Aerovox part no. listing that the part number starts with "SI" if that means anything and that some others in that list start with "P".

From Phil's website:

"Note that two of these types—mica capacitors and flat molded paper capacitors—look similar. Both are flat, often with color coding dots to indicate the value. It is easy to tell them apart by checking the value. Mica capacitors have very small values, typically under .001 mfd. The values of molded paper capacitors will be larger, similar to other paper capacitors, such as .01 or .02 mfd."

refering to my parts list again on page 2, the first page under the "CAPACITORS" heading it says "Capacity values given in the ratings column are in mfd. for Electrolytic and Paper Capacitors, and in mmfd. for mica and ceramic capacitors."

When I read "1500" in the "cap. rating" columm I'm not sure if that's mfd. or mmfd.

[Phil Nelson]

The 1500 in the Sams parts list and schematic means MMFD. The header at the beginning of the capacitor section says, "Capacity values given in the rating column are in mfd. for electrolytic and paper capacitors, and in mmfd. for mica and ceramic capacitors."

That value, plus the square shape, tell me this is a mica cap, which I would not replace at this time.

Anything is possible, but in my experience, flat plastic-coated paper caps are rectangular, not square.

Many micas have colored dots, but some do not, and to add to the fun, more than one color coding scheme was used. It's possible that your cap once had colored dots, but the paint flaked off or faded.

I would replace the electrolytic and paper capacitors and worry about this one later.

Phil Nelson

[jeyurkon]

I forgot that you were using a Sams. The factory manuals are sometimes more descriptive.

The Sprague part number is for a disk ceramic so it must not be too critical. I agree with Phil that this looks like a Mica capacitor.

[charokeeroad]

"The 1500 in the Sams parts list and schematic means MMFD. The header at the beginning of the capacitor section says, "Capacity values given in the rating column are in mfd. for electrolytic and paper capacitors, and in mmfd. for mica and ceramic capacitors."

Ok I think I'm finally getting it. The fact that it's listed as "1500" tells me that it's a mica or ceramic.. if it was a molded paper cap the value would be higher. The small size (large number because of the listing method) tells me it's a mica or ceramic. For example C11 is probably a mica or ceramic it's listed as 1000.

I see where I could have also made the connection by looking at the schematic which shows C66 capacitor as a 1500 mmf, then looking at the chart and seeing that it was listed as 1500 would tell me it's a mica or ceramic. The reverse also being true that if I saw it on the schematic as a 1500 mmf and the parts list showed it as .00015 I could think it was a molded paper cap but that listing would give me doubt because of the small size..

Could I conclude that by looking at the schematic and the parts list I could make a list of the Caps I would want to replace and then go look over the chassis for confirmation?

[Phil Nelson]

You got it.

Phil Nelson

[ChrisW6ATV]

Originally Posted by charokeeroad

if I saw it on the schematic as a 1500 mmf and the parts list showed it as .00015 I could think it was a molded paper cap...

Just to clarify, though, 1500pF (picofarads) (called 1500mmF back then, micro-microfarads) is the same value as .0015 uF (microfarads). A value of .00015, though never written that way, would equal 150pF or 150mmF. The way I memorized these translations is that I remember there are six digits between a microfarad and a picofarad (or mmF). So, 001500 in this case. 1500 mmF or .0015 uF.

[Phil Nelson]

And, for decimal-place-challenged types like me, there are also handy charts like this one:

http://www.justradios.com/uFnFpF.html

Phil Nelson

[charokeeroad]

Chris, After thinking I had it, I looked at that statement again last night and tried to match it with the cap chart, I could see that there was a mistake there. I did a little searching online and realized that there is a six zero difference as you pointed out between micro and micro micro, or pico not three. With a little practice today I should be able to get it streight. If not I can always fall back on a calculator like Phil offered. I have some good tools now and I think I can start puting my cap list together this week.

It's always reassureing to see info like this from Phil's website: (I'm reposting it here for my own quick reference)

"Capacitance values are expressed in units called farads, named after the British physicist Michael Faraday. The capacitors found in radios and TVs have values in tiny fractions of a farad.

A microfarad is one millionth of a farad, abbreviated as mfd, mf, µf, or uf.

A picofarad is one trillionth of a farad, abbreviated as pfd, pf, or µµf.

This website generally uses the abbreviation mfd for microfarads and pf for picofarads.

In vintage radios and TVs, capacitors typically have values in these ranges:
•Electrolytic: 1-200 mfd
•Paper: .001-1 mfd
•Ceramic and Mica: less than .001 mfd

Since a picofard is one trillionth of a microfarad, to convert from microfarads (mfd) to picofarads (pf), you move the decimal point six places to the right. For example:

.47 mfd = 470,000 pf

If you don't like doing such conversions in your head, you can look up the values in this handy chart from Justradios.com."

Thanks!

John

[charokeeroad]

After matching the schematic with the components list I did a visual check of the chassis. As best I can determine these are the caps that need to be replaced. I couldn't find every capacitor. One or two I couldn't find on the schematic and a couple I couldn't find on the chassis but I think all the ones that need to be replaced will be replaced. I would appreciate any feed back.

Thanks

John

[ChrisW6ATV]

As you may already know, you can use 47uF capacitors to replace the 40s and 50s, 100uF to replace the 80uF, and 22uF for the 20s. Similar nearby values are usually good for the paper caps as well (.022 to replace .02 or .025, etc.).

[charokeeroad]

I went to Mouser's website this morning and was able to find all the electrolytics by either making combination or just getting the right size. Looks like justradios will have the rest. I noticed that a repair was made at some point and a non electrolytic cap was used where the schematic called for an electrolytic. I wonder if the set ever worked after that...

Are there certain areas within the set that are likely to need to have resistors replaced, like in the high voltage area or around certain tubes. If so I can order them with the capacitors.

John

[ChrisW6ATV]

The resistors needing replacement are most often higher-value ones (perhaps 100,000 ohms and higher) in any circuit, as opposed to those in particular areas. They often go bad by becoming more than 20% higher in resistance than their original value. To some degree, you can test most resistors without disconnecting them, since the value you measure in-circuit would likely never be higher than the resistor value alone. 100K and higher are the yellow multiplier, green multiplier, and blue multiplier ones (the third stripe counting from the end where the stripes start). When I do tests, though, I test every resistor and also have found lower-value ones that have drifted higher.

[charokeeroad]

Hi Chris, I was wondering about about how I should test the resistors. As I recall from my service days working on Hawk Missile radar at least one leg of the resistor needed to be removed to get an accurate reading. I think you've got it right, if the resistor being tested is one of highest valuse then it would be possible to get a reading on it without removing one leg. As one goes down the value scale probably some other resistors would begin to add values to the reading. If one of then high value resistors did test high the at that point it would be worth while to pull one leg and test it again.

[Phil Nelson]

People have different styles, but I normally do the basic recapping and then try out the TV before worrying about resistors. Nine times out of ten, the majority of resistors are OK and don't need replacement.

Resistors are generally more reliable than capacitors. Also, there are some circuits where the exact value wasn't that critical in the first place. In that case, even if a resistor's value has drifted to, say, 30% above its ideal value, the TV will work normally, and replacing the resistor won't noticeably improve anything.

One exception is a horizontal circuit that determines frequency, where exact values are important. If you want to check resistors before ordering caps, I'd check those around V19, the horizontal AFC/oscillator tube, especially R79 and R80.

I'd stay away from the RF and IF areas until after you finish recapping. In some of those, the lead dress -- exact location of every component and wire -- can be important. Messing with them for no good reason may force a realignment that wouldn't otherwise be necessary.

Old resistors typically go bad when they go open or their values drift high, so often what you're looking for is higher than normal test readings.

When you test a resistor without disconnecting it, then other components wired in parallel with it might make the total resistance value lower. They can't make it higher. That tells us two things:

1. If the tested value is high, then that resistor is probably high.

2. If the tested value is low, then that resistor might be low, normal, or even high, depending on what things are wired in parallel with it. To learn more, you can either disconnect the resistor or analyze the things wired in parallel and calculate the total resistance of all of them.

Most resistors had a manufacturing tolerance of +-20%, so the resistor is considered good if its value is 20% or less, above or below the ideal. If a specific resistor must be more precise, that's usually mentioned in the schematic ("5%" or whatever).

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html