Replace 25 Year Old Metalized Polycarbonate Film Cap? - diyAudio
Go Back   Home > Forums > Design & Build > Parts

Parts Where to get, and how to make the best bits. PCB's, caps, transformers, etc.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 15th December 2011, 02:29 PM   #1
diyAudio Member
 
PreCD's Avatar
 
Join Date: Sep 2011
Location: USA
Default Replace 25 Year Old Metalized Polycarbonate Film Cap?

I have a older preamp in which I replaced all the electrolytics in. I have two 4.7uf 100v MKCs that are used as bypass for my power capacitors, 6800uf 50v.

Is it necessary to replace those caps? The replacement for those are a MKP and I have been looking at those from Wima.
  Reply With Quote
Old 15th December 2011, 03:32 PM   #2
diyAudio Member
 
Join Date: May 2005
Location: toronto
The MKC's are fine and not dried out, but the MKP's might sound a little better.
  Reply With Quote
Old 16th December 2011, 09:16 AM   #3
diyAudio Member
 
Join Date: Dec 2005
Location: Kuala Lumpur
Polycarbonates can degrade with age - sometimes the metal film corrodes away and mains types can lose value as spikes burn holes in the film. I have seen them go leaky in high impedance circuits where moisture has got in. All of these faults can be tested with a capacitance meter and checking dc leakage
  Reply With Quote
Old 18th December 2011, 06:05 AM   #4
diyAudio Member
 
PreCD's Avatar
 
Join Date: Sep 2011
Location: USA
I have decided to replace the old MKC caps in the preamp with the recommended MKP. The old MKCs are WIMA brand. WIMA recommends a MKP4 as the replacment. The problem is that they do not have the cap with 30mm lead spacing. Any suggestions for a replacement 4.7uf 100v bypass cap for preamp power supply?
  Reply With Quote
Old 18th December 2011, 08:19 AM   #5
tvi is offline tvi  Australia
diyAudio Member
 
tvi's Avatar
 
Join Date: Apr 2001
Location: Moonee Ponds, Vic, Australia
27.5mm is the standard these days, you can either bend the legs to fit the holes if pcb mounted or drill new holes and fold the lead over.

Regards
James
__________________
The small part of ignorance that we arrange and classify we give the name of knowledge.
Ambrose Bierce
  Reply With Quote
Old 18th December 2011, 11:28 AM   #6
Elvee is offline Elvee  Belgium
diyAudio Member
 
Elvee's Avatar
 
Join Date: Sep 2006
Quote:
Originally Posted by PreCD View Post
I have decided to replace the old MKC caps in the preamp with the recommended MKP. The old MKCs are WIMA brand. WIMA recommends a MKP4 as the replacment. The problem is that they do not have the cap with 30mm lead spacing. Any suggestions for a replacement 4.7uf 100v bypass cap for preamp power supply?
That makes me think of people "restoring" ancient furniture by replacing the precious walnut veneer by formica, just in case it might be damaged but not visibly.
__________________
. .Circlophone your life !!!! . .
♫♪ My little cheap Circlophone© ♫♪
  Reply With Quote
Old 18th December 2011, 12:10 PM   #7
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Elvee,
I love you !

Polycarbonate, when they were readily available, were (very?) good amongst their peers.

I would not change them unless I knew they were out of specification.
__________________
regards Andrew T.
  Reply With Quote
Old 18th December 2011, 01:42 PM   #8
diyAudio Member
 
PreCD's Avatar
 
Join Date: Sep 2011
Location: USA
Quote:
Originally Posted by Elvee View Post
That makes me think of people "restoring" ancient furniture by replacing the precious walnut veneer by formica, just in case it might be damaged but not visibly.
I favor Walnut! Thanks for the input. Please give a suggestion as to what would be a good bypass capacitor in a preamp power stage. 6800uf 50v power caps currently bypassed with WIMA MKC 4.7uf 100v cap.

From yours and Andrews suggestion that the caps are timeless if proven not to be out of spec I may just leave them alone. I am trying to improve the sound quality of my system and this is one of the easier items to replace to see if it improves. I have a nice audible "hiss" when the preamp is switched on.Get a foot away and you can't hear it but I am concerned that it is a symptom that could be displaying itself at other times of the music. Could be many things but without proper test equipment replacing caps is a good option for me.

Last edited by PreCD; 18th December 2011 at 01:51 PM.
  Reply With Quote
Old 18th December 2011, 02:11 PM   #9
diyAudio Member
 
QSerraTico_Tico's Avatar
 
Join Date: Oct 2004
try ebay
http://www.ebay.nl/itm/Wima-MKC-4-7u...a#ht_500wt_951

http://www.ebay.nl/itm/2x-VISHAY-ERO...#ht_1128wt_702

Last edited by QSerraTico_Tico; 18th December 2011 at 02:14 PM.
  Reply With Quote
Old 18th December 2011, 02:26 PM   #10
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Listen to and measure the hiss when the input of the amplifier is shorted.
Now substitute a 1k0 resistor for that short and listen and measure hiss again.

Now go though your various sources connecting one at a time and one channel at a time and listen and measure the hiss.

Are any of your source/s noisier than the 1k0 resistor?
Are any as quiet as your 1k0 resistor?

Choose the quietest source and now listen and measure the hiss with both channels connected.

Any difference?
__________________
regards Andrew T.

Last edited by AndrewT; 18th December 2011 at 02:30 PM.
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Electrolytic Cap can I replace with film patfont Solid State 19 22nd June 2014 07:48 PM
My RH84 Build - first amp after a 25 year break -:) prelius Tubes / Valves 4 9th June 2011 01:58 AM
FS : Wima 1.0uF 63V Metalized Cap for CD Mod xtaltech Swap Meet 28 3rd August 2008 03:11 PM
Seeking source for metalized film I_Forgot Planars & Exotics 7 15th April 2005 05:04 PM
How do I replace this 40+ year old selenium rectifier? darren01 Tubes / Valves 21 23rd June 2004 12:11 AM


New To Site? Need Help?

All times are GMT. The time now is 02:23 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright ©1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2