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Why Replace Old Paper Capacitors?

Ernst Erb Jürgen Stichling Bernhard Nagel 
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Forum » Technique, Repair, Restoration, Home construction ** » Checks before putting on power » Why Replace Old Paper Capacitors?
Omer Suleimanagich
Omer Suleimanagich
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30.Jun.08 03:49

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Many who prefer not to change original paper capacitors because they think that sound quality is diminished with new poly capacitors, might not be aware at how much paper degradation can occur from time(due to the acid in the paper).


Please take a look at the attachment


Jeffrey Angus
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30.Jun.08 08:06

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Several years ago, I decided I wanted to listen to my parents old Artone console. And I had been hearing the "If you change all the caps first, you're not a technician" nonsense on one of the other forums. So, I plugged it in. Pffft. One down. Change that. Turn it back on. Pfffft. ok, change that one. Turn it back on. Pffft. I'm beginning to see a pattern here.

The moral of the story, from then on, EVERY radio I work on gets recapped first. Then I can trouble shoot what ever is wrong with it. Three things: Wax paper capacitors, electrolytic filter capacitors and selenium rectifiers. They ALL get replaced before I work on the radio.

Interestingly enough, except for the occasional bad tube or broken coil wire, the radios fire right up and work. Some quite well without having to t do anything else except check alignment.

Emilio Ciardiello
Emilio Ciardiello
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30.Jun.08 17:27

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Hello to everybody!

my personal opinion is to leave original components when they work. It does not have sense to buy a ‘Silver Ghost’ Rolls Royce and replace its engine with a brand new Fiat one, just because the original one could have some backlash.
Since early sixties I handled hundreds and hundreds of electronic equipment. In my experience, few times I found defective capacitors, usually dried aluminum capacitors in the power supply or leaky film capacitors in RC coupling amplifiers. I remember just one selenium rectifier replaced. On the contrary, I remember a lot of troubles hard to solve and failures due to bad tampering by some inexperienced technician.

Old radios suffer from the age itself, but also from improper storage environment: dust, temperature and moisture often found in the basement, where they were stored for half a century. All the parts are more or less damaged. Most of the components are hygroscopic and have adsorbed moisture: cotton coated wires, windings, transformers and their insulating paper layers, carbon resistors, ceramic and paper capacitors. Other parts, as contacts and mechanical devices, are dirt, oxidized or rusted.

I remember that also brand-new military components asked for a preforming treatment after a prolonged storage. High temperature baking was indicated by the manufacturers for, say, Allen Bradley composition resistors or for Beckman multi-layer ceramic capacitors. Aluminum capacitors required a reforming treatment of the dielectric after 6 or 12 months of shelf-life. Another point to consider is that a good designer carefully selected each component for some characteristic: DC or AC voltages, ripple currents, temperature coefficient, tolerance. Some components, such as those in a push-pull amplifier, were carefully factory matched. Any replacement today should require a careful evaluation of the substitute part: and often the selection is limited the few components suited for tube equipment.

The radio should be first carefully inspected and cleaned; then a reforming of the aluminum capacitors should be performed, while monitoring the bias conditions of some tubes at reduced supply voltages. On the contrary most people start inserting the plug in the AC outlet: the first result is a blown fuse. Then they change the old fuse with another, stronger one, and the result is more spectacular than fireworks, with dense smoke in the room and a smell of well roasted resistors, transformers and rectifiers.

A slow and controlled power-on of an old radio should result in a safe wake-up and stabilizing of all the components; most of the times no part substitution is required. And it is very satisfying to see all original parts working again. After all, if someone believes that only new components work fine, he can buy a brand new Chinese radio.

Regards, Emilio
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