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Old 27th May 2019, 5:04 pm   #21
defender
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Default Re: Eddystone 840C

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For use in the 'That Capacitor' position, it doesn't need to be ceramic... there are actually several families of ceramics and some can be a bit leaky. Unless you know just which ceramic you've got I'd suggest not using it for anything important. Plastic film capacitors are fine in this place. Common 'mylar' type will do nicely. Most people up them to 630v rated parts. 10nF won't be a very big one and will cost pennies.
Would these do as a "that capacitor"?

0.01uF 630V 10% AXIAL JB Capacitors Polyester Capacitors
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Old 27th May 2019, 5:07 pm   #22
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Default Re: Eddystone 840C

Certainly!
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Old 27th May 2019, 5:43 pm   #23
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Default Re: Eddystone 840C

Cool thanks

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That Black cap is a bit suspect and the red/black electrolitics look as if they have seen better days.
That is before you find all the out of spec resistors.
Black cap?
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Old 27th May 2019, 5:55 pm   #24
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Default Re: Eddystone 840C

Those red/black plastic cased electrolytics were made by Plessey and are well known on this forum. Most people have them on their 'replace on sight' hitlist They are well past their known probable lifespan.

You also have a number of Hunts' paper capacitors in that photo, and they are now well past their reliable period.

You may want to consider a pre-emptive strike. It depends on how reliable you want the receiver to be. I'd do the Plessey electrolytics anyway. They've probably dried out by now and the old set will sound better with its bass back.

It's one of those 'where do you stop once you've started' games.

The capacitors they used in that period ironically suffered from lack of water in the electrolytics, while the paper capacitors died from moisture ingress. You just can't win.

I have my Eddystone EA12 to have a go at one of these days.

David
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Old 27th May 2019, 6:24 pm   #25
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Default Re: Eddystone 840C

The black cap is middle bottom .1uF 500V
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Old 27th May 2019, 6:30 pm   #26
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Default Re: Eddystone 840C

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Those red/black plastic cased electrolytics were made by Plessey and are well known on this forum. Most people have them on their 'replace on sight' hitlist They are well past their known probable lifespan.

You also have a number of Hunts' paper capacitors in that photo, and they are now well past their reliable period.

You may want to consider a pre-emptive strike. It depends on how reliable you want the receiver to be. I'd do the Plessey electrolytics anyway. They've probably dried out by now and the old set will sound better with its bass back.
The plessey caps are marked for the hit list G6TANUKI warned me about them taking a valve out.
I'm going to start by replacing the main ones that can do damage and the ones that will obviously be bad and then plug it in.
I have a US converter transformer that might act as an isolation transformer so I might use that and set the jumper to 110v not sure if its beefy enough though as I don't know how many amps it will take but it has 2 500ma fuses in the mains so it cant be a lot.
Checked it and its got 1 500ma and one 3a fuse in it
I'm planning to lamp limit it too.
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Old 27th May 2019, 6:47 pm   #27
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Default Re: Eddystone 840C

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The black cap is middle bottom .1uF 500V
That's on the hit list it goes to the tone control C71 I believe.
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Old 27th May 2019, 7:04 pm   #28
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Default Re: Eddystone 840C

Be Careful,I would not think without checking first that the 110V transformer is isolated.
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Old 27th May 2019, 7:48 pm   #29
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Default Re: Eddystone 840C

Most US converter transformers are 'autotransformers' a single 240v winding with a tap at 110v. This type gives no isolation whatsoever. They are common because they give the most power throughput rating for a given size of core and weight of copper.

David (an Almondbury lad!)
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Old 27th May 2019, 9:48 pm   #30
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Default Re: Eddystone 840C

It was an idea

I went to school in Almondbury.
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Old 27th May 2019, 9:56 pm   #31
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Default Re: Eddystone 840C

Ah, well better to find out now than the painful way. You could post a 'wanted' for a proper isolating transformer. It seems like there's one changing hands on here every couple of months.

Down Fernside, or down the hell-hole?

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Old 27th May 2019, 11:55 pm   #32
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Default Re: Eddystone 840C

I might give the wanted a try or be very careful.

Down Fernside.
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Old 29th May 2019, 9:45 am   #33
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Default Re: Eddystone 840C

As the set looks in good and (thankfully) unbodged condition, being careful following a few capacitor changes will at least show whether it's worthwhile pursuing further overhaul. I've a 670A here with a very similar PSU/chassis arrangement (other than a selenium, rather than thermionic, rectifier), I use it with a 1:1 mains transformer. As the half-wave rectification used in both sets puts a DC component through the secondary, using a transformer with a generous VA rating is sensible, I use a 250VA ex-BT "Mains Conditioning Transformer"- these were available in large quantities very cheaply a while back but unfortunately the snake-oil folk have cottoned on to them and want lots of money now.

You might find a 230V 1:1 isolater (often red GRP container as opposed to yellow GRP as used for 110V "site" types) fairly cheaply- the set will work at 110V but 230V will give good HT for optimum performance.
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Old 29th May 2019, 11:13 am   #34
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Default Re: Eddystone 840C

RS sold their 240v 1:1 isolator in a yellow grp box ... the 13A socket on it was the give-away if the label had come off.

Whatever you get, test it carefully before relying on it.

David (fully paid-up coward)
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Old 11th Jun 2019, 12:42 am   #35
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Default Re: Eddystone 840C

Just on with the caps that need replacement and I went near the cz1 thermistor as it looked like it had a very hard life and it crumbled away.
So I need to find a replacement, any ideas?
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Old 11th Jun 2019, 5:45 pm   #36
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Default Re: Eddystone 840C

Those Thermistors/Brimistors are long since extinct. Yes, they lead a seriously-hard-and-hot life so tend to crumble if you look at them in the wrong way.

[In my case the wire-winding soldered to the plated ends had pulled the plating off the barrel of the Brimistor].

On my 840A I worked out the total heater-string voltage needed by the valves and then replaced the Brimistor with one of the ceramic-cased 5-Watt 'coffin' resistors of the right value. After three years of near-daily use like this - "Steady Eddy" being my bedside radio - no untowards side-effects have come to light.
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Old 11th Jun 2019, 7:22 pm   #37
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Default Re: Eddystone 840C

Let's have a see... what needs doing:

1) Replace those two Plessey red-and-black electrolytics
2) That black/Brown Hunts capacitor
3) Decide on a resistor value to replace that Brimistor, get and fit

4) Then I'd recommend fitting an IEC connector to take a common power cable... those Eddystone ones are getting hard to find. It'll mean filing out the hole in the chassis to fit it.

I've made a mistake. I could have brought all the necessary bits down with me if I'd thought of it before setting off last week. My junk box is quite good and I've a good isolating transformer. I'm not far away at the moment.... Town End, and could have dropped them in. Sorry.

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Old 11th Jun 2019, 7:32 pm   #38
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Default Re: Eddystone 840C

I've replaced 5 so far 3 Plessey, 1 dark green hunts
And THAT capacitor.
I should have an isolation transformer this week.
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Old 10th Sep 2019, 9:19 pm   #39
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Default Re: Eddystone 840C

Got myself a new brimistor so I should be able to power it up soon, couple more caps to replace first.
Got an old variac to bring it up slowly.
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Old 10th Sep 2019, 10:17 pm   #40
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Default Re: Eddystone 840C

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That is before you find all the out of spec resistors.
HamishBoxer isn't kidding. The only Eddystone I have had through my hands was very "deaf", mostly caused by those horrible little carbon comp resistors going OOT( mostly high-some very high). I must have changed about a dozen of them.
Check them all, especially the ones over about 10K, particularly if they are designed to have a reasonable potential across them.
Unfortunately some were very hard to get at, as they were under coil banks etc.
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