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Old 22nd May 2020, 10:10 pm   #1
A_W_TYE
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Default Stella 239U. Capacitor ID.

Hi All,


Would someone confirm for me that this cap is

820pf, it's not in the caps list.


Thank you.
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Old 22nd May 2020, 10:20 pm   #2
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Default Re: Which cap

Looks far too big to be 820pF. If it was that value I'd expect it to be a ceramic or mica. That is an ordinary paper capacitor dipped in pitch. Have you any means of measuring it? What Philips set is it out of and what part of the circuit did you remove it from?

What are it's physical dimensions? It could be 8,200pF, 82,000 pF (.082uF) or even 820.000pF (0.82uF) but it's probably too small for the last suggestion.
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Old 22nd May 2020, 10:43 pm   #3
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Default Re: Which cap

Hi,


Sorry don't have my head on tonight it measures 620pf,
it's from a Stella ST243u not sure which part of the circut
it is but it connects to 23 on the waveband switch,
and the only ones I can see are C41 and 42 in that part of the circuit
and they are 330pf's.

It measures inch long.
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Old 23rd May 2020, 12:44 am   #4
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Default Re: Which cap

Don't just snip capacitors from the radio without first confirming where they are in the circuit, what their function is and what value the circuit diagram states they should be, otherwise you're going to end up in a real mess. I would agree that it looks very much what I would expect a typical Philips paper capacitor to look like between the ranges of something like 0.01uf and 0.1uf, but I'm prepared to be surprised!

PS, is that 400 volts or 4,000 volts?
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Old 23rd May 2020, 6:53 am   #5
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Default Re: Which cap

Well if it does connect to 23 on the switch, that is the AM/FM switch-over contact. 23 is connected to the audio output and de-emphasis components of the of the FM detector. The circuit layout is not very clear but there are no capacitors of 820pF shown or infact 8,200pf shown in the components list.

It's probably an open-circuit paper cap rated at 400V......you will note that all low-value ceramics are typical tubular types.....common in Philips and Stella sets. That will not be an 820pF....paper types typically start at 1000pF.

I suppose the question to ask is, does the set work at all? Does it work without that capacitor? You say it connects to '23' on the switch. First of all make sure it is 23. Where does the other end of the cap connect?

It could of course be a modification in later production. Maybe the only way to find out is to see if another member has one of these sets and can take a look.
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Old 23rd May 2020, 9:03 am   #6
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Default Re: Which cap?

The picture seems to read 820Epf, Don't know the significance of the E but the physical size suggests something bigger than 820pf which as mentioned earlier would most likely be a tubular ceramic.
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Old 23rd May 2020, 9:26 am   #7
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Default Re: Which cap?

Markings decoder for Philips black wax dipped axial paper capacitors - info that I have:

First Letter: working voltage =

L = 125 V
No letter = 400 V
H = 600 V
S = 800 V
T = 1000 V

Capacitance value in pF is (i.e. 56K = 56000pF)

Then tolerance code:

A = + - 10%
P = + - 20%

Example:

A capacitor with the marking: "S 10 CP 5.1" = 10nF at 800V 20% tolerance.

This is followed by a production code (5.1 for example), which is not of interest.
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Old 23rd May 2020, 10:59 am   #8
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Default Re: Which cap?

The chart starts at 1000pf so did they do caps with lower values?
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Old 23rd May 2020, 11:04 am   #9
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Default Re: Which cap?

Hi All.


Sorry about snipping the cap out but I could not find information on it
so tried to see if I could see what was written on it.
Anyway,this morning before I rose I was thinking what was on the trader sheet and the layout of the radio, there was hardly anything matching.

Well I finally realised I had downloaded the wrong trader sheet,ie Stella 243u,not 239u.
Now I have the correct sheet I may be able to get progress, the cap in question as per trader sheet is 820pf, sorry about confusion.
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Old 23rd May 2020, 11:05 am   #10
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Default Re: Which cap?

Quote:
Originally Posted by vidjoman View Post
The chart starts at 1000pf so did they do caps with lower values?
I would have thought it unlikely for paper dielectric types. Ceramic would be the usual "go to" dielectric for values lower than 1000pF.

The "E" in 820EpF is curious!
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Old 23rd May 2020, 12:01 pm   #11
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Default Re: Which cap?

Hi


Would a cap of 1000uf ie 1nf fit in here, as I have read 20% is a max
to go over and this would be more than 20%.


Thanks
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Old 23rd May 2020, 12:49 pm   #12
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Default Re: Which cap?

Unless my eyes are deceiving me, there is a tolerance value of 10% showing below the "820EpF". That means that any replacement should ideally be between 738pF and 902pF, but I would be surprised if this was critical (I could be wrong). if the set was working with the capacitor at 620pF, that was already ~24% lower than the stated value. If indeed the set was working, why not just put the cap back in? A few bits of extra wire or one of those tinned-copper-wire joining devices should do it, if space is limited and just bending the wires together isn't possible.
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Old 23rd May 2020, 12:57 pm   #13
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Default Re: Which cap?

Colin Hi,

The set has been stored away for a long time,it was not working when I got it not quite sure, what was wrong with it at the time.
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Old 23rd May 2020, 1:41 pm   #14
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Default Re: Which cap?

What you SHOULD do is to first look at the circuit to see if there's any 'critical' capacitors that are going to cause serious damage if they're leaky or short circuit and replace these ONLY! you then do proper fault finding to see why the radio doesn't work. Once you have the set working, you can then, and ONLY then decide what other parts need to be replaced to improve performance and future reliability.

There really is only one way to go about things - and that's as described above. Just replacing components willy-nilly is likely to just end in disaster...trust me!
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Old 23rd May 2020, 3:07 pm   #15
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Default Re: Which cap?

Quote:
Originally Posted by Techman View Post
What you SHOULD do is to first look at the circuit to see if there's any 'critical' capacitors that are going to cause serious damage if they're leaky or short circuit and replace these ONLY! you then do proper fault finding to see why the radio doesn't work. Once you have the set working, you can then, and ONLY then decide what other parts need to be replaced to improve performance and future reliability.

There really is only one way to go about things - and that's as described above. Just replacing components willy-nilly is likely to just end in disaster...trust me!

I was just going to replace the pitch ones, as they are cracked and disintergrating plus the smoothing caps.
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Old 23rd May 2020, 4:01 pm   #16
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Default Re: Which cap?

Quote:
Originally Posted by A_W_TYE View Post
Hi


Would a cap of 1000uf ie 1nf fit in here, as I have read 20% is a max
to go over and this would be more than 20%.


Thanks
1000uF is not 1nF.

1nF is 1000pF or 0.001uF

Can you confirm what the correct model number of the radio is, please?
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Old 23rd May 2020, 4:50 pm   #17
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Default Re: Which cap?

Quote:
Originally Posted by dazzlevision View Post
Can you confirm what the correct model number of the radio is, please?
Please!! Otherwise we have total confusion. At the moment I don't know what circuit to look at. Perhaps you could also take a photo of the underside of the set showing where you cut the capacitor from.
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Old 23rd May 2020, 4:50 pm   #18
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Default Re: Which cap?

There is only one 820pF cap shown on the circuit and that is C47, shown with one end to ground, the other to R19 and to switch contact 19. Those pitch covered caps in Philips/Stella are notorious for become leaky in the electrical sense and what you do about that is a personal choice. They can only be tested for leakage on an insulation tester at their rated working voltage, and even if they aren't leaky now and their capacitance is within their stated range of +/- 10%, given that they're now at least sixty years old, personably, I wouldn't spend time testing them - I'd be swapping them. I say that based on my own experience of these Stella pitch encapsulated caps. As an example, below are pictures of a Stella ST105U I restored - the first is the underside of the chassis with the caps in place - the second shows them after removal and replacement. On some, the pitch had fallen off in places. I tested them out of curiosity at their rated Voltage on my Victor VC60B insulation tester and they all leaked like sieves. One or two had basically morphed into high value resistors.

It's always wise to change components one at a time and check as you go along rather than just yank them out in one go.

How we approach component replacement is a personal decision. Some people just want to 'mend it', 'do it up a bit', 'get in going', 'repair it' or whatever. I have no problem with that approach, but personally, I only ever fully restore a radio, replacing any out of spec components, and perished insulated wiring, because radio restoration is my hobby. I always make a simple 'cradle' on which to mount the chassis so I can work on it and carry out tests safely and if a set doesn't interest me enough to want to fully restore it and keep it, it would never come into my possession and I wouldn't even bother fishing it out of a skip. My view is that routinely replacing paper caps on the sets I restore - whether waxy or pitch coated - isn't a slapdash approach, it's systematic and methodical restoration based on my experience of how such capacitors behave after more than six decades since they came off the assembly line.

As to your Stella ST239U, perhaps the most critical capacitor - the audio coupling capacitor (.022uF).

First pic below shows the underside of my ST105U unrestored chassis.
Second pic is the pitch caps I removed and replaced.
Third pic shows just one cap passing several mA at 150V (that was on my capacitor reformer which I use to reform electrolytics).
Fourth pic is the chassis mounted on a cradle.
The last pic is after restoration. It was an unsafe non-working heap when I got it but it isn't now.

Every success with your set Alan, whatever approach you take.
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Old 23rd May 2020, 5:40 pm   #19
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Default Re: Stella 239U. Capacitor ID.

Quote:
Originally Posted by A_W_TYE View Post
Well I finally realised I had downloaded the wrong trader sheet, ie Stella 243U, not 239U.
Thread title updated and my post referring to the incorrect model deleted.
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Old 23rd May 2020, 5:50 pm   #20
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Default Re: Which cap?

Quote:
Originally Posted by Sideband View Post
Quote:
Originally Posted by dazzlevision View Post
Can you confirm what the correct model number of the radio is, please?
Please!! Otherwise we have total confusion. At the moment I don't know what circuit to look at. Perhaps you could also take a photo of the underside of the set showing where you cut the capacitor from.

Hi all.

Stella 239U as in post #9.

Sorry should have been 1000pf, I have sourced a replacement.

My apologies to all.
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