Forums :: Resources :: Features :: Photo Gallery :: Vintage Radio Shows :: Archives :: Books
Support This Site: Contributors :: Advertise


It is currently Jul Mon 16, 2018 3:22 pm


All times are UTC [ DST ]





Post New Topic Post Reply  [ 16 posts ] 
Author Message
 Post subject: Why do you use film,mylar, caps insted of all ceramic
PostPosted: Dec Sun 31, 2017 7:20 pm 
Member

Joined: Dec Tue 08, 2015 12:53 am
Posts: 317
Location: shirley NY...Long Island
Hello, just wondering why you cant just use all ceramic caps in the restore of a radio...in all the places except for the electrolytic s...instead of different kinds like, Mylar, orange drop, film, etc.

Kenny


Top
 Profile  
 
 Post subject: Re: Why do you use film,mylar, caps insted of all ceramic
PostPosted: Dec Sun 31, 2017 8:04 pm 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 4200
Location: Charleston, W.Va.
Hi Kenny,
Here is the short answer, without getting too technical: It depends upon the type of radio, and the application of the cap within the radio. Modern solid-state gear with relatively low voltages often use ceramic disc caps exclusively. But sometimes ceramic caps show surprisingly high drops in capacitance with high applied DC voltage, even when that voltage may be within their rating. There are some places in a typical antique tubed radio where this does not apply (some bypass applications, for example), and ceramic caps can be used successfully. But where higher voltages are present, especially in the audio stages, it is best to stay with film caps as per the original design. That is, unless you want to start experimenting with using higher values of ceramic caps to compensate for drop-off in capacitance at higher voltages, a process which I do not recommend for routine restoration work.

By the way, when you use the terms "Mylar, orange drop, film, etc." you are talking essentially about the same type of cap, just using different terms.

_________________
Poston


Top
 Profile  
 
 Post subject: Re: Why do you use film,mylar, caps insted of all ceramic
PostPosted: Dec Sun 31, 2017 8:14 pm 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 8464
Location: Baltimore, MD
Poston Drake wrote:
By the way, when you use the terms "Mylar, orange drop, film, etc." you are talking essentially about the same type of cap, just using different terms.


The only difference in those is usually the packaging! :lol:

As Poston said, some ceramic caps have more drop in capacitance at higher voltages. At lower voltages, they are usually ok. That said, ceramic disc caps started appearing in radios in the '50s, but it's important to look at the circuitry they are used in.

Personally, I like to restore a set to as close to factory appearance as possible, which means re-stuffing the old components with new. Axial film caps are usually the only choice for this type of work.

_________________
Tom

PM me for my email address


Top
 Profile  
 
 Post subject: Re: Why do you use film,mylar, caps insted of all ceramic
PostPosted: Dec Sun 31, 2017 9:31 pm 
Member
User avatar

Joined: Jan Mon 18, 2010 2:13 am
Posts: 16648
Location: Dayton Ohio
One exception to the use of ceramics in place of mylar/poly would be if they are NP0 or C0G types.

This is their temperature coefficient which there are many.
NP0/C0G are the most stable ceramics.
They will not loose capacitance value with voltage applied as others do. They are also quite pricey...
I used them in restuffing the caps of my Zenith 617 with EXCELLENT results!

Here is the thread on the topic.

http://www.antiqueradios.com/forums/vie ... 9&t=263757

I wanted to restuff Cornell-Dubilier "Cub" capacitors and keep the wooden dowel intact. This is virtually impossible with mylar/poly caps, so I investigated the use of C0G ceramic surface mount caps.

More here
http://www.theradiofox.com/zenith/1933/617/index.html

-Steve

_________________
Radio Interests
-Zenith
-Sparton
-Pre-War FM
Consoles and floor models, the bigger, the better!


Top
 Profile  
 
 Post subject: Re: Why do you use film,mylar, caps insted of all ceramic
PostPosted: Dec Sun 31, 2017 9:37 pm 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 32883
Location: Maryland 20709, USA
One problem with ceramic caps as regards selecting replacement parts is the huge range of tolerances available. They run from quite precise to GMV (Guaranteed Minimum Value).

Ceramic caps, properly selected for the application, are the most precise electronic parts made.

As to their suitability for tube-type gear, ceramics were used extensively in high-end tube equipment from Collins and other manufacturers for military and aerospace applications. One reason for this is that a disc ceramic cap with short leads has a much higher self-resonant frequency then any tubular cap can achieve.

To address the thread's title question...
I do not sub modern caps for ceramics.
I replace any ceramics in the original design with ceramics.
But the original caps are usually still good, so no replacement needed.

- Leigh

_________________
73 de W3NLB
http://www.AtwaterKent.info
Click "Grebe Stuff" for Synchrophase info


Top
 Profile  
 
 Post subject: Re: Why do you use film,mylar, caps insted of all ceramic
PostPosted: Jan Mon 01, 2018 2:50 am 
Member

Joined: Jun Fri 01, 2007 9:46 pm
Posts: 224
Location: Chattanooga, TN
The Knight Star Roamer was produced with all ceramic caps (except for variables, filter, one audio bypass and one mica).
My guess is that was done for economic reasons.

vince


Top
 Profile  
 
 Post subject: Re: Why do you use film,mylar, caps insted of all ceramic
PostPosted: Jan Mon 01, 2018 5:28 am 
Member

Joined: Jun Fri 19, 2009 6:34 pm
Posts: 7733
Location: Long Island
What you have to understand is, there's more to a capacitor than just uF's and volts. There are a whole host of "secondary characteristics" such as dissipation factor, Q, leakage resistance, temperature coefficient (tempco), ESR, ESL, and self resonant frequency. Some of these characteristics differ markedly among the different kinds of capacitors. Circuit designers were aware of all this and took these characteristics into consideration when they selected the capacitors that were used in their radios.

Now if you want to repair an old radio so it works like it did when new, it's important to use replacement parts that have the same characteristics as the originals. Tubular mylar (polyester) caps have characteristics which are closer to the original paper capacitors that were used in many radios than most other capacitor types available today, so they work well out well as replacements for paper caps in many situations. Of course if one has to replace a ceramic cap, the best thing to use would be a new ceramic cap with the same characteristics.

_________________
"Hell, there are no rules here--we're trying to accomplish something!"

Thomas A. Edison


Top
 Profile  
 
 Post subject: Re: Why do you use film,mylar, caps insted of all ceramic
PostPosted: Jan Mon 01, 2018 7:38 am 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 27835
Location: SoCal, 91387
Chris108 wrote:
What you have to understand is, there's more to a capacitor than just uF's and volts. There are a whole host of "secondary characteristics" such as dissipation factor, Q, leakage resistance, temperature coefficient (tempco), ESR, ESL, and self resonant frequency. Some of these characteristics differ markedly among the different kinds of capacitors. Circuit designers were aware of all this and took these characteristics into consideration when they selected the capacitors that were used in their radios.

Remember, these were consumer grade circuits with +/- tolerances of 15%, and with the exception of one or a few mica's in the front end, damn near every set I've seen simply used non-polarized tubular wax caps, outside of the Electrolytic's.
Chris108 wrote:
Now if you want to repair an old radio so it works like it did when new, it's important to use replacement parts that have the same characteristics as the originals. Tubular mylar (polyester) caps have characteristics which are closer to the original paper capacitors that were used in many radios than most other capacitor types available today, so they work well out well as replacements for paper caps in many situations. Of course if one has to replace a ceramic cap, the best thing to use would be a new ceramic cap with the same characteristics.

I've found that either Metalized Polypropylene, or Radial Film, can replace a non-polarized unit, and the set will perform as it should, regardless of which type is used.

_________________
\\\\\\\\\\\\\\\\\\\\\\\\He Who Dies With The Most Radios Wins//////////////////


Top
 Profile  
 
 Post subject: Re: Why do you use film,mylar, caps insted of all ceramic
PostPosted: Jan Mon 01, 2018 2:17 pm 
Member
User avatar

Joined: Jan Tue 31, 2012 1:55 am
Posts: 4394
Location: Mountains of Mourne. Ireland.
viewtopic.php?p=2625913#p2625913

Image

Leigh wrote: That's a neat chart, Greg. Thank you.

One point of disagreement . . .

Disc ceramic capacitors are generally avoided in audio circuits due to piezoelectric effect.

Under some circumstances they can generate voltage if subjected to physical force, like sound waves.

This phenomenon is totally irrelevant when they're used at RF frequencies.



For additional information, see complete discussion here.

Greg.


Edit: image updated.


Last edited by egg on Apr Thu 26, 2018 7:25 pm, edited 1 time in total.

Top
 Profile  
 
 Post subject: Re: Why do you use film,mylar, caps insted of all ceramic
PostPosted: Jan Mon 01, 2018 3:18 pm 
Member

Joined: Jun Fri 19, 2009 6:34 pm
Posts: 7733
Location: Long Island
Quote:
Remember, these were consumer grade circuits with +/- tolerances of 15%, and with the exception of one or a few mica's in the front end, damn near every set I've seen simply used non-polarized tubular wax caps, outside of the Electrolytic's.


This is very true, however, the question was, "why not just use ceramic capacitors everywhere?" The problem is, regardless of the merits (or lack thereof) of paper capacitors, that is what the manufacturers of antique radios used in great abundance. That's what they designed for, and optimized around. If you were to replace all the paper caps in radios with ceramics, which have much sharper Q's and higher self resonant frequencies than tubular caps, at least some of those circuits would experience problems with instability and oscillation.

Quote:
I've found that either Metalized Polypropylene, or Radial Film, can replace a non-polarized unit, and the set will perform as it should, regardless of which type is used.


Metalized polypropylene is a type of dielectric; radial film is a type of lead termination that could be used with any dielectric. Polypropylene is in many ways an ideal dielectric on many counts, but for fixing old radios it is sometimes too good. Its dissipation is about a tenth of polyester, which is in turn about a quarter of that of paper. Meaning that under the right circumstances, you could end up with the same kinds of instability as if you used ceramic caps! Unless you are working on a high frequency shortwave or FM radio, polyester (mylar) does not seem to be a problem in the majority of applications, so I stick with that.

_________________
"Hell, there are no rules here--we're trying to accomplish something!"

Thomas A. Edison


Top
 Profile  
 
 Post subject: Re: Why do you use film,mylar, caps insted of all ceramic
PostPosted: Jan Mon 01, 2018 3:31 pm 
Member
User avatar

Joined: Jun Wed 08, 2011 2:33 am
Posts: 6848
Location: Ohio 45177
I like the EGG Chart. Clarifies things without alot of explanation.


Top
 Profile  
 
 Post subject: Re: Why do you use film,mylar, caps insted of all ceramic
PostPosted: Jan Mon 01, 2018 7:47 pm 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 27835
Location: SoCal, 91387
Greg's chart is interesting, but if you'll notice, just about everything -capacitor style specific- has nothing to do with garden variety AA5's or TRF's. Bypass and coupling -the most commonly used for these sets- can be handled by any of the three. As I stated above, it really doesn't matter which, and certainly a ceramic disc cap could be tried in a circuit, and left in, if there were no ill effects.

_________________
\\\\\\\\\\\\\\\\\\\\\\\\He Who Dies With The Most Radios Wins//////////////////


Top
 Profile  
 
 Post subject: Re: Why do you use film,mylar, caps insted of all ceramic
PostPosted: Jan Tue 02, 2018 4:11 am 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 4478
Location: Perrysburg, OH, U.S.A.
Here's a snippet combined from the Mouser website when "Film Capacitors" is selected:
Attachment:
Film Cap Dielectrics.jpg
Film Cap Dielectrics.jpg [ 30.38 KiB | Viewed 1050 times ]

This doesn't include Teflon film which are hard to find and EXPENSIVE!
John

_________________
“Never attribute to malice that which can be adequately explained by stupidity.”
― R. A. Heinlein


Top
 Profile  
 
 Post subject: Re: Why do you use film,mylar, caps insted of all ceramic
PostPosted: Jan Mon 08, 2018 3:29 am 
Member

Joined: Dec Tue 08, 2015 12:53 am
Posts: 317
Location: shirley NY...Long Island
And Chris108 it is a Hallicrafters SX-71 I am working on...wow ..alot of very good answers here....

KNY


Top
 Profile  
 
 Post subject: Re: Why do you use film,mylar, caps insted of all ceramic
PostPosted: Jan Mon 08, 2018 3:29 am 
Member

Joined: Dec Tue 08, 2015 12:53 am
Posts: 317
Location: shirley NY...Long Island
I double posted sorry about that..so I typed this in place..cause I didnt know how to completely delete a post


Last edited by Kennynva on Jan Mon 08, 2018 3:31 am, edited 1 time in total.

Top
 Profile  
 
 Post subject: Re: Why do you use film,mylar, caps insted of all ceramic
PostPosted: Jan Mon 08, 2018 5:16 am 
Member

Joined: Jun Fri 19, 2009 6:34 pm
Posts: 7733
Location: Long Island
In a high frequency shortwave set like an SX-71, which ostensibly goes up to 66 MHz, it really pays to stick with what they did originally, and do not replace what you don't have to. The original mica and ceramic capacitors are very likely still good and should be left alone unless one is found to be bad through troubleshooting.

The paper caps are probably either bad or on their last legs. There are some places where old paper caps can be left in if they haven't gone open (cathode bypass circuits for example), but unless you have the test equipment and patience to vet each cap properly, it is safer and more satisfactory to just replace them all with new ones. As mentioned above, polyester (mylar) caps should work out well as replacements as long as you maintain the original placement and lead dress. If the original electrolytics are still connected they are almost certainly worn out, but the radio makes no special demands on those caps and they can easily be replaced with new ones.

_________________
"Hell, there are no rules here--we're trying to accomplish something!"

Thomas A. Edison


Top
 Profile  
 
Post New Topic Post Reply  [ 16 posts ] 

All times are UTC [ DST ]


Who is online

Users browsing this forum: No registered users and 5 guests



Search for:
Jump to:  
























Privacy Policy :: Powered by phpBB