Orange SRC capacitors - How reliable? - UK Vintage Radio Repair and Restoration Discussion Forum

Martin G7MRV · 19th Nov 2023, 11:14 am

The Wartime Civilian Receiver I'm working on contains three 0.1uF capacitors made by S.R.C. These are a little over an inch long cylindrical and about half an inch wide, orange cement covered.

Can anyone comment on the reliability of these at all?

I don't have a leakage tester, and besides they are tightly wrapped to the terminal strip so removing them just to test would be a pig. I do have plenty of modern polyesters to replace them with if required, but if I were to go at the set that deeply without just cause, then I may as well strip out the resistors as well and near enough do a total rebuild! I'm absolutely certain most of the resistors will be well out of tolerance but the set is reasonably functional and I'm hoping the issues it was having have been solved by getting that hideous Hunts waxy out.

I have a feeling though that these may be from an earlier restoration and likely to be OK?

Craig Sawyers · 19th Nov 2023, 11:23 am

SRC is Stability Radio Components. Lots of info in one of the topics here https://www.vintage-radio.net/forum/...ad.php?t=32293

They are possibly polyester film https://mullard.org/products/stabili...various-values

More info here https://www.basildon.com/history/ind...the-1960s.html

Craig

dazzlevision · 19th Nov 2023, 12:10 pm

These look very similar (apart from body colour) to the Mullard/Philips C296 "mustard" series of axial lead Polyester film dielectric capacitors. Thorn fitted them in their mid-to-late 1960s three speed, four track tape recorders (several of which I have overhauled) and I have not found any to be out of spec.

I think the dielectric is almost certainly Polyester.

paulsherwin · 19th Nov 2023, 12:18 pm

As you say, these will have been fitted as part of an earlier repair/restoration, maybe around 1970.

Plastic film caps are usually completely reliable, though there are a few 60s types which look like polyester but aren't. The best approach is to power up and check for signs of DC leakage, particularly with the couplers.

G6Tanuki · 20th Nov 2023, 6:44 pm

Quote:

Originally Posted by paulsherwin

Plastic film caps are usually completely reliable, though there are a few 60s types which look like polyester but aren't. The best approach is to power up and check for signs of DC leakage, particularly with the couplers.

Indeed; there were 'mixed dielectric' capacitors produced in the 50s and 60s that I learned not to trust.

Sprague [of all people!] produced several ranges of these - see attached, from a 1967 ARRL handbook...

Maarten · 20th Nov 2023, 9:24 pm

Depending on the exact construction, mixed dielectric capacitors might not leak at all. In that case deterioration of the paper will usually increase the capacity outside of the normal tolerance, dielectric losses might be higher and they may eventually break down at lower than maximum working voltage.

19th Nov 2023, 11:14 am	#1
Martin G7MRV Heptode Join Date: May 2008 Location: Selby, North Yorkshire, UK. Posts: 840	Orange SRC capacitors - How reliable? The Wartime Civilian Receiver I'm working on contains three 0.1uF capacitors made by S.R.C. These are a little over an inch long cylindrical and about half an inch wide, orange cement covered. Can anyone comment on the reliability of these at all? I don't have a leakage tester, and besides they are tightly wrapped to the terminal strip so removing them just to test would be a pig. I do have plenty of modern polyesters to replace them with if required, but if I were to go at the set that deeply without just cause, then I may as well strip out the resistors as well and near enough do a total rebuild! I'm absolutely certain most of the resistors will be well out of tolerance but the set is reasonably functional and I'm hoping the issues it was having have been solved by getting that hideous Hunts waxy out. I have a feeling though that these may be from an earlier restoration and likely to be OK? __________________ I got food in ma belly and a license for ma telly My Blog - http://g7mrv.blogspot.com

19th Nov 2023, 11:23 am	#2
Craig Sawyers Dekatron Join Date: Nov 2010 Location: Oxford, UK. Posts: 4,861	Re: Orange SRC capacitors - How reliable? SRC is Stability Radio Components. Lots of info in one of the topics here https://www.vintage-radio.net/forum/...ad.php?t=32293 They are possibly polyester film https://mullard.org/products/stabili...various-values More info here https://www.basildon.com/history/ind...the-1960s.html Craig __________________ Doomed for a certain term to walk the night

19th Nov 2023, 12:10 pm	#3
dazzlevision Dekatron Join Date: Sep 2003 Location: Near Swindon, North Wiltshire, UK. Posts: 3,490	Re: Orange SRC capacitors - How reliable? These look very similar (apart from body colour) to the Mullard/Philips C296 "mustard" series of axial lead Polyester film dielectric capacitors. Thorn fitted them in their mid-to-late 1960s three speed, four track tape recorders (several of which I have overhauled) and I have not found any to be out of spec. I think the dielectric is almost certainly Polyester.

19th Nov 2023, 12:18 pm	#4
paulsherwin Moderator Join Date: Jun 2003 Location: Oxford, UK Posts: 27,127	Re: Orange SRC capacitors - How reliable? As you say, these will have been fitted as part of an earlier repair/restoration, maybe around 1970. Plastic film caps are usually completely reliable, though there are a few 60s types which look like polyester but aren't. The best approach is to power up and check for signs of DC leakage, particularly with the couplers.

20th Nov 2023, 9:24 pm	#6
Maarten Dekatron Join Date: Dec 2007 Location: Haarlem, Netherlands Posts: 4,051	Re: Orange SRC capacitors - How reliable? Depending on the exact construction, mixed dielectric capacitors might not leak at all. In that case deterioration of the paper will usually increase the capacity outside of the normal tolerance, dielectric losses might be higher and they may eventually break down at lower than maximum working voltage.