Capacitor Installation
I have a Sears, Model 1058, 101.860 radio chassis. The schematic for the radio can be found at
http://www.nostalgiaair.org/PagesByModel/652/M0016652.pdf

Please look at pin #2 of the FM discriminator (6AL5). You should see an electrolytic listed as 4 mfd @ 50V, C36. In my chassis, it is installed with the positive terminal of C36 going to the chassis (ground) and the negative terminal going to pin #2. Does this seem correct to you? The schematic symbol shows the half moon circle going to ground. Was the capacitor installed incorrectly? Your comments, please. I am in the process of replacing all of the electrolytics in the radio.

Thanks,
Jerry

Jerry: Hopefully someone with much more knowledge will respond, but perhaps the schematic is drawn incorrectly since the electrolytic cap probably would have blown if put in backwards. Also, the way caps are drawn has changed over the years. I have never been sure if the rounded side is negative, though it appears that is the intent. When it is drawn with one solid line and the other being a squared "U" shape, then it is clear that the "U" side is the negative side. Mark from Kalamazoo

:Capacitor Installation
:I have a Sears, Model 1058, 101.860 radio chassis. The schematic for the radio can be found at
:http://www.nostalgiaair.org/PagesByModel/652/M0016652.pdf
:
:Please look at pin #2 of the FM discriminator (6AL5). You should see an electrolytic listed as 4 mfd @ 50V, C36. In my chassis, it is installed with the positive terminal of C36 going to the chassis (ground) and the negative terminal going to pin #2. Does this seem correct to you? The schematic symbol shows the half moon circle going to ground. Was the capacitor installed incorrectly? Your comments, please. I am in the process of replacing all of the electrolytics in the radio.
:
:Thanks,
:Jerry
:
Jerry it is installed right. Notice all other cap symbols are the same, except the variable ones. The schematic just doesn't indicate polarity. And I believe they used the wrong e-cap symbol for the time.
Bill

Rounded side is negative/ground/outside foil/frame side, depending on the capacitor. Always has been. Always will be. Many schematics do not use this type of symbol. However, when it is used, this is how it's used.

T.

My circa 1930 westinghouse only uses the rounded line (with an arrow on the end)for the adjustable ones. Fixed ones use two straight lines. My pre WWII Zenith, 1930's Crosley, and 1930's RCA uses only two straight lines for all caps, but the adjustable ones have an arrow draw through them at a 45 degree angle. My 1937 Philco uses two straight lines for fixed caps, a straight and rounded line for adjustable caps and the electrolytics use the straight line and u shaped line. My 1950's Zenith uses the rounded line for all caps except the electrolytics. I don't see consistency here. Were there standards that were ignored by the companies? Mark from Kalamazoo

There were and are many ways to represent a capacitor. For instance, the two lines with an arrow drawn through was considered old in 1950. Now, in my electronics class, they use it to represent a variable capacitor (usually a trimmer). ...And they tell me that the curved line with an arrow is antiquated. Seems like the blind leading the blind.

At any rate, there are many different ways to represent various kinds of capacitors. However, for each way, there is a standard, and the standard is followed almost always. I'd like to say always, but I'm sure that there's an exception somewhere. I have yet to see that exception. The curved line with the arrow is always the rotor and is always the frame. The straight line is the insulated stator. Two lines with an arrow drawn at a 45 degree angle......well, .......I really have no clue as to which one is the rotor, which is probably why in 1950 they decided that that symbol was old and should be substituted with the line and curved arrow.

...And regarding fixed capacitors, if there is a curved line, it is always the negative or ground or outside foil side of the capacitor. Otherwise, where no curve is shown, polarity, if any, will be noted.

There are different ways to represent a capacitor, but for each way that way is consistent wherever it is used.

T.

:Rounded side is negative/ground/outside foil/frame side, depending on the capacitor. Always has been. Always will be. Many schematics do not use this type of symbol. However, when it is used, this is how it's used.
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:T.

You are right Thomas. I wish the schematic had a voltage chart. Shouldn't there be some negative voltages associated with the 6AL5?
Bill

Actually, considering that it is being fed from the plate of the 6AL5, it would most definitely be more negative than the chassis. I doubt that any significant voltages are developed here, and so the electrolytic would most likely work well in either direction. Idealy, though, if it is found that the plate of the 6AL5 is indeed negative with respect to the chassis (signal present), then the electrolytic should have its negative side connected to the 6AL5 plate.

:Actually, considering that it is being fed from the plate of the 6AL5, it would most definitely be more negative than the chassis. I doubt that any significant voltages are developed here, and so the electrolytic would most likely work well in either direction. Idealy, though, if it is found that the plate of the 6AL5 is indeed negative with respect to the chassis (signal present), then the electrolytic should have its negative side connected to the 6AL5 plate.
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Thanks Thomas. I guess the cap keeps the negative voltage in check.
Bill

:Capacitor Installation
:I have a Sears, Model 1058, 101.860 radio chassis. The schematic for the radio can be found at
:http://www.nostalgiaair.org/PagesByModel/652/M0016652.pdf
:
:Please look at pin #2 of the FM discriminator (6AL5). You should see an electrolytic listed as 4 mfd @ 50V, C36. In my chassis, it is installed with the positive terminal of C36 going to the chassis (ground) and the negative terminal going to pin #2. Does this seem correct to you? The schematic symbol shows the half moon circle going to ground. Was the capacitor installed incorrectly? Your comments, please. I am in the process of replacing all of the electrolytics in the radio.
:
:Thanks,
:Jerry

After looking at the schematic, and even thinking. I don't see any reason for the capacitor to have been put in positive to ground. It would seem a assembly person just made and error. I would replace the capacitor as shown in the print.

::Capacitor Installation
::I have a Sears, Model 1058, 101.860 radio chassis. The schematic for the radio can be found at
::http://www.nostalgiaair.org/PagesByModel/652/M0016652.pdf
::
::Please look at pin #2 of the FM discriminator (6AL5). You should see an electrolytic listed as 4 mfd @ 50V, C36. In my chassis, it is installed with the positive terminal of C36 going to the chassis (ground) and the negative terminal going to pin #2. Does this seem correct to you? The schematic symbol shows the half moon circle going to ground. Was the capacitor installed incorrectly? Your comments, please. I am in the process of replacing all of the electrolytics in the radio.
::
::Thanks,
::Jerry
:
:After looking at the schematic, and even thinking. I don't see any reason for the capacitor to have been put in positive to ground. It would seem a assembly person just made and error. I would replace the capacitor as shown in the print.

Warren and all:
I agree with Warren, the next model number schematic shows the cap with neg to ground, too.
Lewis

:::Capacitor Installation
:::I have a Sears, Model 1058, 101.860 radio chassis. The schematic for the radio can be found at
:::http://www.nostalgiaair.org/PagesByModel/652/M0016652.pdf
:::
:::Please look at pin #2 of the FM discriminator (6AL5). You should see an electrolytic listed as 4 mfd @ 50V, C36. In my chassis, it is installed with the positive terminal of C36 going to the chassis (ground) and the negative terminal going to pin #2. Does this seem correct to you? The schematic symbol shows the half moon circle going to ground. Was the capacitor installed incorrectly? Your comments, please. I am in the process of replacing all of the electrolytics in the radio.
:::
:::Thanks,
:::Jerry
::
::After looking at the schematic, and even thinking. I don't see any reason for the capacitor to have been put in positive to ground. It would seem a assembly person just made and error. I would replace the capacitor as shown in the print.
:
:Warren and all:
:I agree with Warren, the next model number schematic shows the cap with neg to ground, too.
:Lewis

Correct me if i'm wrong. But I believe that the 6al5 is acting as a rectifier with the IF transformer supplying the ac voltage to be rectified. In a rectifier circuit positive is taken off the cathode and if you needed a negative voltage you would reverse things and take the negative voltage off the plate.
If this was an amplifier stage then the plate would have to be positive to work, but it's a rectifier.
Just my take on it.
Bob Z

::::Capacitor Installation
::::I have a Sears, Model 1058, 101.860 radio chassis. The schematic for the radio can be found at
::::http://www.nostalgiaair.org/PagesByModel/652/M0016652.pdf
::::
::::Please look at pin #2 of the FM discriminator (6AL5). You should see an electrolytic listed as 4 mfd @ 50V, C36. In my chassis, it is installed with the positive terminal of C36 going to the chassis (ground) and the negative terminal going to pin #2. Does this seem correct to you? The schematic symbol shows the half moon circle going to ground. Was the capacitor installed incorrectly? Your comments, please. I am in the process of replacing all of the electrolytics in the radio.
::::
::::Thanks,
::::Jerry
:::
:::After looking at the schematic, and even thinking. I don't see any reason for the capacitor to have been put in positive to ground. It would seem a assembly person just made and error. I would replace the capacitor as shown in the print.
::
::Warren and all:
::I agree with Warren, the next model number schematic shows the cap with neg to ground, too.
::Lewis
:
:Correct me if i'm wrong. But I believe that the 6al5 is acting as a rectifier with the IF transformer supplying the ac voltage to be rectified. In a rectifier circuit positive is taken off the cathode and if you needed a negative voltage you would reverse things and take the negative voltage off the plate.
: If this was an amplifier stage then the plate would have to be positive to work, but it's a rectifier.
:Just my take on it.
:Bob

How 'bout take a hi-z meter and read the polarity when the radio is tuned to a strong station?
Lewis

:Capacitor Installation
:I have a Sears, Model 1058, 101.860 radio chassis. The schematic for the radio can be found at
:http://www.nostalgiaair.org/PagesByModel/652/M0016652.pdf
:
:Please look at pin #2 of the FM discriminator (6AL5). You should see an electrolytic listed as 4 mfd @ 50V, C36. In my chassis, it is installed with the positive terminal of C36 going to the chassis (ground) and the negative terminal going to pin #2. Does this seem correct to you? The schematic symbol shows the half moon circle going to ground. Was the capacitor installed incorrectly? Your comments, please. I am in the process of replacing all of the electrolytics in the radio.
:
:Thanks,
:Jerry
:

::Capacitor Installation
::I have a Sears, Model 1058, 101.860 radio chassis. The schematic for the radio can be found at
::http://www.nostalgiaair.org/PagesByModel/652/M0016652.pdf
::
::Please look at pin #2 of the FM discriminator (6AL5). You should see an electrolytic listed as 4 mfd @ 50V, C36. In my chassis, it is installed with the positive terminal of C36 going to the chassis (ground) and the negative terminal going to pin #2. Does this seem correct to you? The schematic symbol shows the half moon circle going to ground. Was the capacitor installed incorrectly? Your comments, please. I am in the process of replacing all of the electrolytics in the radio.
::
::Thanks,
::Jerry
::
Hello All –

First, thanks to all for your responses. Quite an interesting discussion. When I posted my question, I did not take the time to examine the circuit closely. So, this is my take on it. If you draw an equivalent circuit of the DC path for current, this is what I think you would fine. Assume the top half of T5 is positive and the bottom half is negative during one-half cycle. Then this places pin 7 (the anode of one diode) at a positive potential and pin 5 (the cathode of the other diode) at a negative potential. This would mean DC current (not electron flow) would flow from ground up through R21 to pin 2, placing pin 2 at a negative potential and hence, C36 would have its negative terminal connected at pin 2. This would be the correct polarities for both diodes to conduct. However, because of transformer action, their conduction are 180 degrees out of phase with each other which provides the discriminator action. My research indicates this type of discriminator is called a ratio detector.

As for the capacitor markings, again my research shows the half circle is considered an outer foil for some capacitors and is usually connected to ground. This was done to so the capacitor when mounted in this fashion, the outer shield would act as a shield for signal isolation. And, because of this, it is usually considered the negative terminal. It appears in this vintage radio, the accepted method to mark electrolytics was not yet adopted.

Anyway, it was nice of all of you to weigh in on my post.

Jerry

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:I never did tune into that discussion, since I thought it was about some type of capacitor or some like related situation.
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:On that sets DISCRIMINATOR circuit, and after all of the bouncy-bouncy back and forth possibilities, did you eventually get that electrolytic summing capacitor installed in the correct manner. . .which it initially was in. . . . from its factory installation.
: The elects + goes to ground.
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:Refer to the newer # 1065 Silvering-tone model, which wasn't quite so chintzy on parts count and utilized the more common series matched pair of loading resistors to then establish a tap for metering. That then is accomplishing the infinitely easier evaluation of alignment via the use of a VTVM and its zero center viewing capability.
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:That procedure will then let you view the symmetry of the S demodulation curve response with out the need of a scope, sweep generator and matching pad.
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:Heck, you can even spot check alignment by using an off the air, moderate signal strength, FM stations signal.
: Query me if you need more info.
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:Reference thumbnail:
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:73's de Edd
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:Ed –

Thanks for weighing in on the discussion. First, I have not installed the capacitor as I am waiting for other caps to arrive by mail and do them all at one time. However, I am quite interested in your discussion on alignment. I only have a VOM meter and would like to “touch up” my alignment. Now this is what I think I can do.

For AM, I can tune for a weak station and adjust the front end and IFs for a strong signal at the speaker.

For FM, I would think I could do the same in that I could adjust the IFs for a strong signal at the speaker.

However, with my circuit, do you see a way to adjust the S curve using a VOM? If necessary, I could readjust the meter for a zero center reading. But, if I could use my VOM, I would need to take into consideration meter loading since this is not a VTVM.

Anyway, would appreciate your comments on the above and any suggestions.

Thanks,
Jerry
1/14/09

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