What kind of Capacitor is it?

 Hello again.   I have 15-20 of these capacitors, see attachement, and not sure if they are paper or not.   They are pf's and in the mica range.   I have read elsewhere not to change mica caps.  I cannot find anything to tell me if these fall into the paper/wax catogory.   They are silver in color with a red or black band at one end, covered in a clear plastic.  Should I change these?  Hope I do not have too. 

 Regards  Joseph

Attachments:

• DSC_2319-2 (68 KB)

To thank the Author because you find the post helpful or well done.

To thank the Author because you find the post helpful or well done.

Hi John.  Thanks.  Glad to know I do not have to change them also.    I have had to unsolder on the same terminal that they were on, but used an aligator clip as a heat sink..  Did not see any melting. 

  Thanks again.

 Regards:  Joseph

To thank the Author because you find the post helpful or well done.

For Styroflex caps the color rings give the rated voltage, but the values are different, depending on the capacitor type. See reference books, e.g. Siemens Pocket Book.

In general the blue ring is the lowest rating, about 25V =;
next is yellow for up to 63V=
red ring is  for ca 60V~ /100 to160V=;
green for 160 to 250V=, and
black may stand for200V~/500 to 630V=.

Note: The AC/DC ratios appear a bit illogical. They are just taken from a.m. reference book (issue 1966/67) for different capacitor types.
Not every type is made for all the ratings mentioned.

 

To thank the Author because you find the post helpful or well done.

May I add a few comments on Polystyren Capacitors?

PERFORMANCE

I have never found it necessary to replace one except where a carelessly placed soldering iron has damaged one.  Yes - I have been guilty too!    Their stability is excellent and checks have usually found them to be within a fraction of 1%.

Their temperature coefficient is between -60 and -250 parts per million per degree C.  The nominal coefficient for most is -150.  The low-voltage (smaller) ones tend to be slightly less stable in the long term and with temperature.  I have found this coefficient useful in achieving frequency stability of tuned circuits by opposing positive coefficients of inductors.

Since the sealing is usuually imperfect, (and perhaps the film is permeable?) humidity does have an effect.   Long-term damp storage can affect capacitance.  A figure of "+30 to +60 parts per million per cent increase in relative humidity" is quoted by Standard Telephones and Cables. This could add to problems in trying to align a set taken from a damp environment!

The dry resistance is specified as better than 10⁶ Megohms.

All are easily damaged by heat, but LCR introduced a device with a more tolerant film but had a slighty inferior temperature coefficient of capacitance.

LABELLING 

 Most that I have seen do not have coloured bands and usually have the legends located so as to need a mirror to see!  There seems to be no consistent marking scheme. 

LCR Components who made may of the capacitors in the UK, identify with the capacitance in pF and two letter code:-

Tolerance

F   1pF

H   2.5%

J  5%

K  10%

M  20%

 

Voltage

Z  30V

X  160V

V  400V

U  630V

Hence 470 JX  would be 470pF +5% 160Volt dc working.

The Coding for STC (ITT) is not logical for their 455-LWA-103 to 111 and 303  to 311 devices and takes some 17 pages of data!  

Roy

 

To thank the Author because you find the post helpful or well done.

Hello Roy. 

           Thanks for that info.  I do not believe I damaged any with an iron but I did get close. There were a few paper caps next to these.    I am almost ready to see if the work I did, replacing all paper and elecrolytic caps,  fixes the problem with one of the ELL80 tube plates glowing red.  Just waiting on 1 cap. 

  Anyway I am relieved that I do not have to replace these Polystyrene caps, about 25 of them.

 Thanks again for the feed back!

Regards:  Joseph

To thank the Author because you find the post helpful or well done.