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


It is currently Aug Mon 03, 2020 4:33 pm


All times are UTC [ DST ]





Post New Topic Post Reply  [ 16 posts ] 
Author Message
 Post subject: Replacing ceramic discs with polypropylene?
PostPosted: Sep Thu 12, 2019 2:19 am 
Member

Joined: Nov Tue 15, 2011 11:19 pm
Posts: 534
Location: Woolwich Twp (Swedesboro), NJ
I am working on a old Nordmende, and there are 3 ceramic discs that are falling/flaking apart. I was just barely able to ID them as .0047uf (4700pf), because of their difficult location and my 52 year old eyes are getting worse.

Question is, I have .0047uf polypropylene laying around. Can use them? A google search was inconclusive. The audiophile people must be nuts. Other say you should use ceramic in bybass or temp sensitive circuits. Problem is, I cannot ID where they are in the schematic. So I am asking the experts here.


Top
 Profile  
 
 Post subject: Re: Replacing ceramic discs with polypropylene?
PostPosted: Sep Thu 12, 2019 4:24 am 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 35390
Location: SoCal, 91387
Simply note which tube circuit they are in, and then you should be able to ID them on the print. I would definitely replace like for like in this case, esp if they are in the osc circuit. The manufacturer used disc caps in the locations they are in, for a reason.

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


Top
 Profile  
 
 Post subject: Re: Replacing ceramic discs with polypropylene?
PostPosted: Sep Thu 12, 2019 7:44 pm 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 3898
Location: Charleston, W.Va.
Hi N4NYY,
I agree with above advice by "fifties". Assuming that this radio is original, the significant thing is that only three ceramic disc caps were used. As "fifties" says, this was no doubt done for a reason. You were fortunate to be able to identify their value; perhaps this will help in identifying them in the schematic. But in any case, I would definitely use ceramic discs for their replacement.

_________________
Poston


Top
 Profile  
 
 Post subject: Re: Replacing ceramic discs with polypropylene?
PostPosted: Sep Thu 12, 2019 7:58 pm 
Member

Joined: Nov Tue 15, 2011 11:19 pm
Posts: 534
Location: Woolwich Twp (Swedesboro), NJ
That is the reason I ask the experts. I will replace with the same.


Top
 Profile  
 
 Post subject: Re: Replacing ceramic discs with polypropylene?
PostPosted: Sep Thu 12, 2019 9:27 pm 
Member

Joined: Sep Tue 15, 2015 1:16 am
Posts: 886
Location: 18424 PA
Have you unsoldered 1 end and tested them? American disc caps don't go bad that often. Euro disc should be about the same quality or better. On the other hand, i have seen Euro oil caps that you would think are good and have tested bad for leakage.


Top
 Profile  
 
 Post subject: Re: Replacing ceramic discs with polypropylene?
PostPosted: Sep Thu 12, 2019 9:51 pm 
Member

Joined: Nov Tue 15, 2011 11:19 pm
Posts: 534
Location: Woolwich Twp (Swedesboro), NJ
n3uvt wrote:
Have you unsoldered 1 end and tested them? American disc caps don't go bad that often. Euro disc should be about the same quality or better. On the other hand, i have seen Euro oil caps that you would think are good and have tested bad for leakage.


They are flaking and cracked. One split into half.


Top
 Profile  
 
 Post subject: Re: Replacing ceramic discs with polypropylene?
PostPosted: Sep Thu 12, 2019 11:13 pm 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 5976
Location: Montvale NJ, 07645
N4NYY wrote:
I am working on a old Nordmende, and there are 3 ceramic discs that are falling/flaking apart. I was just barely able to ID them as .0047uf (4700pf), because of their difficult location and my 52 year old eyes are getting worse.

Question is, I have .0047uf polypropylene laying around. Can use them? A google search was inconclusive. The audiophile people must be nuts. Other say you should use ceramic in bybass or temp sensitive circuits. Problem is, I cannot ID where they are in the schematic. So I am asking the experts here.


You don't state whether all (most) of the capacitors are ceramic, or just the 3 and they are flaking.
If there are only 3 ceramics and the rest are film caps, then the chances are they were used for a reason.


Top
 Profile  
 
 Post subject: Re: Replacing ceramic discs with polypropylene?
PostPosted: Sep Thu 12, 2019 11:16 pm 
Member

Joined: Nov Tue 15, 2011 11:19 pm
Posts: 534
Location: Woolwich Twp (Swedesboro), NJ
Scott wrote:
N4NYY wrote:
I am working on a old Nordmende, and there are 3 ceramic discs that are falling/flaking apart. I was just barely able to ID them as .0047uf (4700pf), because of their difficult location and my 52 year old eyes are getting worse.

Question is, I have .0047uf polypropylene laying around. Can use them? A google search was inconclusive. The audiophile people must be nuts. Other say you should use ceramic in bybass or temp sensitive circuits. Problem is, I cannot ID where they are in the schematic. So I am asking the experts here.


You don't state whether all (most) of the capacitors are ceramic, or just the 3 and they are flaking.
If there are only 3 ceramics and the rest are film caps, then the chances are they were used for a reason.



The 3 discs are flaking cracking. The other ceramic caps look more like a dogbone resistor shape. They all look good. They are not disc, despite being the same value.


Top
 Profile  
 
 Post subject: Re: Replacing ceramic discs with polypropylene?
PostPosted: Sep Thu 12, 2019 11:42 pm 
Member
User avatar

Joined: Sep Mon 16, 2013 2:42 am
Posts: 4052
Location: Tucson, Arizona U.S.A.
Quote:
The audiophile people must be nuts.

+1 to that.

As others have said, we can't help you choose the type to use if we don't know where they are in the circuit. So the best advice is replace them with the same type.

Parts that are broken in half need to be replaced. The problem is how did it get that way? If it was physically abused, just replace it. But i have seen ceramic capacitors burn in half or even burn completely away leaving only the wires. If that happened, you really need to determine where they are in the circuit so we can guess at what happened and what to do about it. Otherwise, it may happen again.

In general, ceramic capacitors are very reliable and seldom need to be replaced.

_________________
Jim Mueller


Top
 Profile  
 
 Post subject: Re: Replacing ceramic discs with polypropylene?
PostPosted: Sep Thu 12, 2019 11:55 pm 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 5976
Location: Montvale NJ, 07645
N4NYY wrote:
The 3 discs are flaking cracking. The other ceramic caps look more like a dogbone resistor shape. They all look good. They are not disc, despite being the same value.


Ok, so it sounds like you have tubular ceramics elsewhere. I would be thinking that maybe these were used to achieve a particular temperature coefficient that was not available in the tubular ones. Not knowing where they are in the circuit makes it important to replace only with ones of the same temperature coefficient- just in case. If you knew where they were, you could make a decision based on their use in the circuit.


Top
 Profile  
 
 Post subject: Re: Replacing ceramic discs with polypropylene?
PostPosted: Sep Fri 13, 2019 5:19 am 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 35390
Location: SoCal, 91387
Jim Mueller wrote:
Quote:
The audiophile people must be nuts.

+1 to that.

As others have said, we can't help you choose the type to use if we don't know where they are in the circuit. So the best advice is replace them with the same type.

Parts that are broken in half need to be replaced. The problem is how did it get that way? If it was physically abused, just replace it. But i have seen ceramic capacitors burn in half or even burn completely away leaving only the wires. If that happened, you really need to determine where they are in the circuit so we can guess at what happened and what to do about it. Otherwise, it may happen again.

In general, ceramic capacitors are very reliable and seldom need to be replaced.

The best course of action is to buy at least two or three of each value. If the first replacements burn out, you'll have backups to use once you determine the cause of the problem. Ceramic caps are quite cheap.

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


Top
 Profile  
 
 Post subject: Re: Replacing ceramic discs with polypropylene?
PostPosted: Sep Fri 13, 2019 12:15 pm 
Member

Joined: Jun Fri 19, 2009 6:34 pm
Posts: 9664
Location: Long Island NY
It is always the best practice to replace components with the same types originally used. Substituting different parts is essentially random re-engineering. Chances are whoever designed the radio put considerable effort into finding exactly the right capacitors to give the desired level of performance. Put anything else in there and the performance will probably not be the same, and odds are it won't be better.

Even if those ceramic discs are only used as bypass capacitors, they could be critical to proper performance. Capacitors have self resonant frequencies and inductances; no polypropylene cap will match a ceramic disc on those characteristics. If the Nordmende has FM, those things could make the difference between working well and barely usable, or maybe not working. Not only would I use ceramic discs for replacements, I would ensure that the physical size (diameter) of the new ones is the same as the old ones to try to keep the characteristics as close as possible to what was originally there.

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

Thomas A. Edison


Top
 Profile  
 
 Post subject: Re: Replacing ceramic discs with polypropylene?
PostPosted: Sep Wed 18, 2019 2:43 am 
Member
User avatar

Joined: May Sun 13, 2012 8:12 pm
Posts: 14011
Location: Central PA 16801
I have always replaced "like for like". the engineers know more than I do for deciding upon what type of capacitor goes where. they chose a particular style for a reason.

if it were a ceramic disc, it gets replaced with a ceramic disc.

if it were a foil/film capacitor, it gets replaced with a foil/film capacitor.

if it were a silver mica capacitor, it gets replaced with a silver mica capacitor with close to matching temp coefficients.

so on and so forth...

steve

_________________
You have enemies ? Good. That means you've stood up for something, sometime in your life.
-Churchill


Top
 Profile  
 
 Post subject: Re: Replacing ceramic discs with polypropylene?
PostPosted: Sep Wed 18, 2019 3:08 pm 
Member
User avatar

Joined: Oct Thu 04, 2018 2:11 pm
Posts: 384
Location: Suburban Chicago
N4NYY wrote:
The audiophile people must be nuts.


No, no, no, the audiophile's know what they are talking about! However this is RF and if you use poly caps in RF circuits your highs will be brittle and your lows will be muddy. Polite people do not even speak of what they do to the mids....

Seriously however, ceramic caps are generally better for RF applications. They may make little difference in the AM band but at the high end of the HF band they could make a big difference. If these caps are in the audio section then you could use polys but even there they sometimes serve as RF bypass caps so at the end of the day the best practice is to always replace like with like. If you are really keen to get a radio going today we will grant you dispensation to try whatever you have on hand until the proper replacements arrive!


Top
 Profile  
 
 Post subject: Re: Replacing ceramic discs with polypropylene?
PostPosted: Sep Wed 18, 2019 7:52 pm 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 35390
Location: SoCal, 91387
khutch wrote:
Polite people do not even speak of what they do to the mids....

Thx for the belly laugh! :wink:

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


Top
 Profile  
 
 Post subject: Re: Replacing ceramic discs with polypropylene?
PostPosted: Sep Wed 18, 2019 9:46 pm 
Member

Joined: May Sat 06, 2006 4:03 am
Posts: 3606
Location: ZIP 23831 South of Richmond, VA 25 miles down the pike.
I don't see mention of the model number or a link to schematic.

Bill J.


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 9 guests



Search for:
Jump to:  


































-->


Privacy Policy :: Powered by phpBB