Replace old ceramic caps advice

[AndrewGM]

I want to replace some 30 year old ceramic disc caps and don't
understand the values printed on them and therefore what to replace them with in terms of value or type.
Metalised polyester ?

It says 103 P on them.

Any help and suggestions.... apart form leave them alone ?

Also, how much can I increase the uf value of my existing PS smoothing caps ?
I have IN 5408 rectifiying diodes, which have a high spec, before
the 10,000 uf 63 v Aerovox caps ( 12 years old )
Can I go 15,000 or even 22,000 uf safely ?

Thanks

And

[duekfx]

Just take them out and measure them and replace them with the same values, don't bother identifying inscriptions.

I don't really know in what application they were used in. I guess it's not a critical location where you'd use ceramic caps, so I'd say PE is a good choice, since they are quite small. PP is even better if there is enough space.

I hope this helps.

[AndrewGM]

Apolgies

They are on a power amp circuit board.

Many thanks for the advice.

And

[duekfx]

Well, in that case I'd stick with PP if they fit. PS would be even better but they have availability issues and they come in small values only. Micas are also a good choice for small values. PE is quite small, but it's not the best type of dielectric, but still better than ceramics. jacco and pooge also favor Class 1 NP0/CG0 ceramics. The choice is yours.

[jaycee]

it's similar to resistors

1 0 then 3 more zeroes

100nF by the sound of it. probably for decoupling.

[duekfx]

Lemme summarize:

Dielectric (in order of preference): Polystyrene/Mica, Polypropylene, Polyester. I don't know where to place the Class 1 NP0/CG0 types since I never tried them.

Size (from small to large): PS/PE (depends), Mica, PP. Those Class 1 ceramics should be the same size as your original ceramics.

Values:
Mica: pF and early nF range
PS: same as mica
PE: wide range
PP: starts in the nF range.

This is in general. There might be exceptions

[andymac62]

Hi, 103P would be a 10n ceramic disc capacitor. Depending on where it is used will determine the voltage rating. Try to get 250V ones.
Ceramic disc are very good for high frequency response, so try to replace them with the same type & size of disc.
Failing that, FKP (metallized polypropylene) should be ok.

Adding larger electrolytics to the power supply will give you slightly more headroom, and the thing to consider is inruch current when they charge up at power on. If you are adding much more capacitance, i suggest you change the 1N5408 to 6A8 diodes. These are 6A and will handle the extra inrush current better.

[duekfx]

This is a quote from Paul J. Stamler's "Replacing Passive Components to Improve Sound Quality"


Ceramic disc capacitors were among the first small caps available and
they're still used in a lot of equipment, especially guitar amps. They
sound terrible, adding a screechy and gritty quality to the high
frequencies that's quite unpleasant. They're also microphonic: a
ceramic disc can pick up vibrations from the air or through the
cabinet and add them (distorted) to the signal. When you find them in
audio circuits it's a good idea to replace them with polystyrene
(best) or polypropylene capacitors.

As always, there are a few exceptions. Ceramic discs are excellent for
bypassing radio frequencies to ground; they're often found connected
between the ground side of an input Jack and the chassis to help keep
radio frequency junk out of the system. If you find ceramic discs used
this way, leave them there. Ceramic discs are also sometimes used on
circuit boards between the power supply pins and ground to keep radio
garbage out of the active circuits. You can replace the ceramic discs
with stacked film or polypropylene caps, but keep the discs around-if
the new units aren't as effective, you may need to put the old ones
back in.

Mica capacitors are even older than ceramic discs and aren't used much
anymore. They behave a lot like ceramic discs and I replace them with
polystyrenes when I find them.

Paper capacitors were often found in equipment built before 1980 and
they're still used in a lot of guitar amps. They tend to sound a
little harsh on the top, muddy on the bottom, and vague in the
midrange. It's usually a good idea to replace them with
polypropylenes, although in a guitar amp you should keep the paper
caps around in case you don't like the change. (Guitar amps, after
all, are _supposed _to add tonal colorations, and your tastes may be
different from mine.)

Polyester capacitors (Mylar, to use the DuPont trade name) have
replaced paper capacitors in most applications; when a piece of
equipment or a speaker says it uses "film" capacitors, they usually
mean polyesters. They're not bad, but the bass tends to be tubby and
the top end vague; they should be replaced with polypropylenes or (in
small values) polystyrenes.

A special class of polyester capacitors is called "stacked film."
These were designed as replacements for ceramic discs in bypass
applications and tend to be quite compact. I do like them for
bypassing, but polypropylene is better in circuits that actually
handle audio. There are stacked polypropylenes on the market, but
they're expensive and hard to find.

Polypropylene capacitors are a mainstay for audio upgrades. Their
quality is excellent, they're reliable, and there are now quite a few
sources for them. For low voltage work, the 50V ECQ-P series from
Panasonic (available through Digi-Key) is excellent, but they only go
up to 0.47pF. Old Colony Sound Labs, Mouser Electronics, Parts
Connection, and Welborne Labs (see addresses at end of article) all
offer a variety of larger polypropylenes at prices ranging from
reasonable to astonishing. A word of caution: polypropylene is an
inefficient material for making capacitors, and polypropylene caps
tend to be larger than polyesters of a similar value. Before you
order, be sure the replacements will fit inside your case!

Polypropylenes come in two types: film and foil, and metallized. The
film and foil types are excellent, but big; the metallized units are
smaller, but some listeners say they don't sound quite as good. (I
remain agnostic on that point.) You should avoid using metallized
polypropylenes in tube circuits that place high DC voltages across
them as they have a reputation for shorting out.

Finally, polystyrene capacitors are the best you can buy easily.
(Teflon caps are reputed to be even better, but unless you're NASA you
probably can't get them in small quantities.) They are only available
in small values (up to about 0.05F), and they're easy to damage with a
soldering iron, but they sound wonderful: clean and clear, with lots
of detail and no treble grunge. Mallory and Mial polystyrenes are
available from Newark and other large distributors, and other
polystyrenes are carried by Parts Connection and Welborne Labs.

[AndrewGM]

Blimey !
What a response - thank you.
Actually this is a project that has erupted into an obsession.
It started life as a Denon PMA 850 MK2.
I removed the pre amp completely and use the remains as a truly astonishing power amp.
I've had had decent things such as Naim 62 Hi Cap 250 and some Meridian kit but this old amp with passive ladder stepped attenuator makes me hold my breath sometimes in a way I never did.
It's a 1979 bit of kit but it is a true dual mono monster, has a huge 420 VA traff wound for L & R and is really easy to work on an learn from too.
Kind of embarrassed at the above admisson but as a novice it's opened up the world of the hobby to me.
Every time I change some old parts to new ones it seems to get better and then I want to do it again but somewhere else !!
Apologies to the grimacing engineers out there !!

The feedback you've all provided is very helpful.

On inrush, there is a relay that holds everything up for 10 seconds
- ish.
Do I still need 6 A 8 diodes ?
Not questioning your knowledge at all - I'll hunt them out and fit them irrespective !

I'm glad I asked for advice now

And

Maybe 20,000 uf too ambitious.... 15,000 as a mid way ?