Completed Project Can a 600V 0.25 MFD old wax capacitor be replaced with two parallel 1000V 0.1MFD film capacitor?

Thread Starter

Rahulk70

Joined Dec 16, 2016
533
Hi folks,

I'm trying to recap the capacitors in my EICO 950B. As of now the tester works fine, but I'm worried that keeping the old capacitors is not a good idea. As stated in the question can it be done.

I've attached the picture of the capacitors & schematics just for reference. Also I'm having hard time finding electrolytic capacitors above 450V in shops and this device has a 525V 8MFD cap. Probably will have to get one from Mouser.com.

Thanks.
 

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AlbertHall

Joined Jun 4, 2014
12,186
C8 => 0.2uF? I think that will be OK. There will be a bit more ripple on the anode of the indicator tube.
For the 8uF, you could use two 16uF in series but you will need some equalising resistors to make sure they share the voltage - perhaps 2x470k.
 

MisterBill2

Joined Jan 23, 2018
13,673
I have one of those EICO testers that I built in about1963, and have had no problems with it yet. Just be very careful about the polarity if you replace any of the capacitors.
 

ian field

Joined Oct 27, 2012
6,536
Hi folks,

I'm trying to recap the capacitors in my EICO 950B. As of now the tester works fine, but I'm worried that keeping the old capacitors is not a good idea. As stated in the question can it be done.

I've attached the picture of the capacitors & schematics just for reference. Also I'm having hard time finding electrolytic capacitors above 450V in shops and this device has a 525V 8MFD cap. Probably will have to get one from Mouser.com.

Thanks.
The caps you propose for replacements aren't even vaguely enough capacitance. You might get lucky and find a couple of old type fluorescent fitting PFC caps that fit the bill. Not electrolytic and performance will be far superior.

Small appliances like set top boxes tend to come in at about 47 - 150uf as reservoirs, but not enough voltage rating. Identical caps in series have less capacitance and more voltage rating, You might find as low as 22uF, but 2 in series will still be a bit OTT capacitance. You'll have to add resistance in series with the rectifier cathode so it doesn't strip during warm up, and you need equal resistors in parallel with each cap to swamp and balance leakage. CFL reservoir caps in S/P combinations could be an absolute last ditch attempt...…...
 

ebp

Joined Feb 8, 2018
2,332
The 8 µF cap is just a power supply filter. Probably the easiest to get would be 10 µF at 600 or 630 V. I see Mouser has an 8 µF 600 V, but it is hideously expensive!
 

ebp

Joined Feb 8, 2018
2,332
I had a look on Digi-Key and 10 µF plastic film types rated at adequate voltage are a small fraction of the cost of the electrolytic that Mouser carries. C4GAHUD5100AA3J is an axial type. I didn't look at physical size. A film cap should be good for at least a hundred years. Mouser probably has similar parts.
 

MisterBill2

Joined Jan 23, 2018
13,673
I am wondering about the C8 capacitor, right below C1, the 8Mfd. But C8 is also shown polarized, at 0.25mFd which seems strange that it would be polarized. So I am suggesting to examine the tester and verify that C8 really IS 0.25 . The circuit seems a bit strange to me. The really critical values are marked "prec" in the bom., I would add C2 to the list of high accuracy caps.
 

Thread Starter

Rahulk70

Joined Dec 16, 2016
533
C8 => 0.2uF? I think that will be OK. There will be a bit more ripple on the anode of the indicator tube.
For the 8uF, you could use two 16uF in series but you will need some equalising resistors to make sure they share the voltage - perhaps 2x470k.
Thank you for the reply. I found this website and I think except the 400V cap(sold only as a big lot), I can get the rest of the caps from this website.
https://www.justradios.com/cart.html
 

Thread Starter

Rahulk70

Joined Dec 16, 2016
533
I have one of those EICO testers that I built in about1963, and have had no problems with it yet. Just be very careful about the polarity if you replace any of the capacitors.
The date code stamped inside the equipment said it was manufactured on Nov 17, 1959. The person who sold it to me on eBay said he was a TV repairman and it was his old gear. On the eBay listing, he said that the device still works fine when tested against good caps. I saw only the 250V electrolytic cap replaced in this device. When I asked him about any restoration he said it's been a while since he used but he said it worked. But I'm worried about using it since it could potentially damage internal transformer or the tube with those dried caps even though it seems to work fine.
 

Thread Starter

Rahulk70

Joined Dec 16, 2016
533
I am wondering about the C8 capacitor, right below C1, the 8Mfd. But C8 is also shown polarized, at 0.25mFd which seems strange that it would be polarized. So I am suggesting to examine the tester and verify that C8 really IS 0.25 . The circuit seems a bit strange to me. The really critical values are marked "prec" in the bom., I would add C2 to the list of high accuracy caps.
I think that C2 might be a precision Mica capacitor. But mica caps are usually very stable, right?
 

Thread Starter

Rahulk70

Joined Dec 16, 2016
533
The caps you propose for replacements aren't even vaguely enough capacitance. You might get lucky and find a couple of old type fluorescent fitting PFC caps that fit the bill. Not electrolytic and performance will be far superior.

Small appliances like set top boxes tend to come in at about 47 - 150uf as reservoirs, but not enough voltage rating. Identical caps in series have less capacitance and more voltage rating, You might find as low as 22uF, but 2 in series will still be a bit OTT capacitance. You'll have to add resistance in series with the rectifier cathode so it doesn't strip during warm up, and you need equal resistors in parallel with each cap to swamp and balance leakage. CFL reservoir caps in S/P combinations could be an absolute last ditch attempt...…...
As you have said the combination of caps will be used only if I'm unable to get one as a single unit. But I think I found a website where I could get something that I want even though it might cost like $3.5 to $4.
 

MisterBill2

Joined Jan 23, 2018
13,673
I think that C2 might be a precision Mica capacitor. But mica caps are usually very stable, right?
Yes, mica caps are both stable and reliable. Silver-mica caps are also very high "Q", but I don't think they were even available in 1959. And this application does not require them.
 

Bernard

Joined Aug 7, 2008
5,784
Back in 1950 CE Co. had 7 seismograph crews , each inst. truck had 24 amplifiers with about 35 mica caps ea.
or around 6,000 caps. Over about 7 years I replaced maybe 15 mica caps, mostly for leakage. Not to bad for reliability.
 

Thread Starter

Rahulk70

Joined Dec 16, 2016
533
Yes, mica caps are both stable and reliable. Silver-mica caps are also very high "Q", but I don't think they were even available in 1959. And this application does not require them.
If you see in the 3rd picture(wax cap1.jpg) there is a color coded cap next to the 400V cap. From its looks I think it’s a mica. I’ll check it later on and confirm.
 
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