Replace 25 Year Old Metalized Polycarbonate Film Cap?

PreCD · 15th December 2011, 02:29 PM

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.

ticknpop · 15th December 2011, 03:32 PM

The MKC's are fine and not dried out, but the MKP's might sound a little better.

davidsrsb · 16th December 2011, 09:16 AM

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

PreCD · 18th December 2011, 06:05 AM

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?

tvi · 18th December 2011, 08:19 AM

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

Elvee · 18th December 2011, 11:28 AM

Quote:

Originally Posted by PreCD

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.

AndrewT · 18th December 2011, 12:10 PM

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.

PreCD · 01:51 PM

Quote:

Originally Posted by Elvee

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.

QSerraTico_Tico · 02:14 PM

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

AndrewT · 02:30 PM

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?

15th December 2011, 02:29 PM	#1
PreCD diyAudio Member Join Date: Sep 2011 Location: USA	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.

18th December 2011, 08:19 AM	#5
tvi diyAudio Member 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 border between the Real and the unreal is not fixed, but just marks the last place where rival gangs of shamans fought each other to a standstill. Robert Anton Wilson

18th December 2011, 12:10 PM	#7
AndrewT 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.

18th December 2011, 02:11 PM	#9
QSerraTico_Tico diyAudio Member 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.

18th December 2011, 02:26 PM	#10
AndrewT 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.


	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

15th December 2011, 03:32 PM	#2
ticknpop 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.

16th December 2011, 09:16 AM	#3
davidsrsb 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

18th December 2011, 06:05 AM	#4
PreCD diyAudio Member 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?

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Electrolytic Cap can I replace with film	patfont	Solid State	16	13th September 2011 11:19 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?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read