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 Post subject: What do I replace this cap with?
PostPosted: Nov Fri 24, 2017 4:23 pm 
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Joined: Apr Thu 13, 2017 11:22 pm
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IMG_2117



Hopefully, this picture posted. if not it is in a Philco 51-1731. this capacitor is Brown tubular (solid, looks a lot like a resistor) with 5 bands. 220pf. Riders 22-77, C5, DC blocking. I tried replacing with a Silver Mica of the same value and tested the set. Reception fell off sharply.
is this the correct type of cap to replace this with, and the new cap threw my alignment way off? Or should i replace with a different type of cap like a ceramic disk or Tantalum? I don't want to get too far ahead of myself in pulling all these caps without proper knowledge.

Regards,
Paul Demming


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 Post subject: Re: What do I replace this cap with?
PostPosted: Nov Fri 24, 2017 4:41 pm 
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If the original was a tubular ceramic, you shouldn't disturb it. They have about the lowest failure rate of any component and it's extremely rare to find one that isn't physically broken that would need replacement for any other reason. A silver mica, or a disc ceramic with exactly the same temperature characteristics as the original (and that is sometimes impossible to obtain) would be good replacements for a bad one.

Many capacitors automatically need to be changed, such as electrolytics and paper types. Typically we do not disturb mica or ceramic caps until and unless they show operational problems which make them suspect. Note that even moving a mica or ceramic cap to read the value can sometimes damage the internal connections from the leads.

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 Post subject: Re: What do I replace this cap with?
PostPosted: Nov Fri 24, 2017 4:43 pm 
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There it is.


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 Post subject: Re: What do I replace this cap with?
PostPosted: Nov Fri 24, 2017 5:40 pm 
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The mica should work OK, but you likely need to touch up the alignment of C10 and C18 after changing it. Or, if you still have the original cap, put it back.

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 Post subject: Re: What do I replace this cap with?
PostPosted: Nov Sun 26, 2017 8:51 pm 
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Location: Santa Clara, CA 95051
Hi Paul,

I am obviously not on the same page with you.
My Riders (CD version) does not have this radio. Philco doesn't have page number 77 in book #22. I did find it on both Beitman and I have a Philco CD which also had it. It says Rider on the bottom of that scan but that's not where I got it.

In the picture you posted are two caps, a bright new orange one marked, .001@600 volts, and an older tubular paper cap that looks just like a resistor centered in the picture with color bars Black, Brown, Red, Red, Silver. You indicate that is “C5,” found on the schematic.

Both copies of this schematic I have are very hard to read but it appears that C5 connects the plate of 6AU6 and the tuning cap.
Am I on the page with you so far?
My obvious confusion is the cap pictured ties to ground and that's not where C5 connects on the print.
In the picture you posted, that old cap looks to be in place from the factory and has not yet been swapped out, but you said you did that so I ask to confirm that you took this picture before you swapped out that cap?

FWIW I have swapped out a handful of those tubular caps with standard ceramic caps and never had a problem. Yes if they were in the front end of the radio I had to align, but I've never had one knock down the reception noticeably.

Tom Albrecht suggested you might have to adjust C10 and C18. Again I wonder if I am looking at the same radio because my print shows C10 as a fixed capacitor, C18 is adjustable.

Thanks for the post, I learn from what all you brilliant guys do. Thanks for sharing your work with me.

Tomie


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 Post subject: Re: What do I replace this cap with?
PostPosted: Nov Sun 26, 2017 9:46 pm 
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Tomie, it's Rider's Volume 21
...and it's correctly connected to pin-five (plate-6AU6). The photo is easy to misinterpret... :)
http://www.nostalgiaair.org/Resources/714/M0013714.htm

Legible double-page schematic.
http://www.americanradiohistory.com/hd2 ... e-0078.pdf

As Dennis has pointed out, it's a ceramic 220pF tubular capacitor. Back in the day one of the recommended replacements was an Erie Ceramicon. Lol.

Greg.


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 Post subject: Re: What do I replace this cap with?
PostPosted: Dec Tue 05, 2017 12:13 am 
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not to reopen an older subject here, but that orange cap was a bad on my part. using a .001uf to replace a 100pf i am told is a bad idea. but the darned thing worked. But now it does not. AM or FM. I have replaced every single component in this set except those old brown caps and one Mica block cap. i know this set was worked on before, and i did find some dubious resistor values.. corrected those. My guess is the set was realligned from factory, and now its way out of alignment. I am currently going component to component to verify all values and then run a signal through it. if i have a problem. i intend to replace those old brown caps with Silver Mica caps. Does anyone see a problem with that swap?


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 Post subject: Re: What do I replace this cap with?
PostPosted: Dec Tue 05, 2017 12:29 am 
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Reading through the thread, I'm not sure exactly what problems you were chasing except that you suspect there might be components not replaced correctly in the past. I didn't try very hard to figure out exactly which capacitor you are now asking about except that I quickly notices you installed a 0.001 mfd in place a an existing 100pf...it "worked" but now not. 0.001mfd is equivalent to 1000pf.

The value of the capacitor suggests it's part of a tuned circuit. Even if you replaced it with an exact value, normal small variation would throw alignment off. So I'd suggest you to attempt an alignment procedure, before moving on.

These mica and ceramic capacitors rarely fail.


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 Post subject: Re: What do I replace this cap with?
PostPosted: Dec Tue 05, 2017 12:45 am 
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your correct 1000pf. missed a zero. As for checking values, double checking my work. Sometimes I'm my worst enemy.


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 Post subject: Re: What do I replace this cap with?
PostPosted: Dec Tue 05, 2017 12:52 am 
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AJJ wrote:
These mica and ceramic capacitors rarely fail.
I certainly agree.

However, "rarely" and "never" are not synonymous.

There was a time when I considered both types to be essentially eternal.
Unfortunately, that's no longer the case for mica caps, as we've seen failure modes.

I believe it is still valid for fixed ceramic caps.

- Leigh

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