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Old 24th May 2019, 8:00 pm   #1
defender
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Default Eddystone 840C

I haven't even done anything constructive to my DAC10 yet and another valve lump had come into my possession.
Mentioned to my mate that I had a valve radio to tinker with and he said he was offered a valve radio but turned it down then he said I'll get it for you.

It turned out to be a receiver with no power plug that probably hasn't seen power for 20 to 30 years, on the plus side there might be one or two valves I can use.
It's full of Hunts capacitors and some are "difficult"
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Last edited by defender; 24th May 2019 at 8:13 pm.
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Old 24th May 2019, 8:08 pm   #2
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Default Re: Eddystone 840c

Please do not scrap it, I have two of these and they are not difficult to sort at all.

Like any set that has not been powered for a long time there are correct procedures.
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Old 24th May 2019, 8:18 pm   #3
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Default Re: Eddystone 840C

They're not bad general SWL sets, worth saving/restoring rather than cannabalising for valves, sturdily made and with an RF stage and a BFO. Do beware of the twin caveats of mains-transformerless ("AC/DC") power supply implementation and metal casework, though- there are various crucial insulating washers and strips to make the set safe and faults or incompetent previous owners could make it dangerous, so thorough insulation testing os important.
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Old 24th May 2019, 8:18 pm   #4
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Default Re: Eddystone 840c

Quote:
Originally Posted by HamishBoxer View Post
Please do not scrap it,I have 2 of these and they are not difficult to sort at all.
Like any set that has not been powered for a long time there are correct procedures.
I daren't power it up direct to the mains I have a couple of 60w bulbs but no power lead for it.
Quote:
Originally Posted by turretslug View Post
They're not bad general SWL sets, worth saving/restoring rather than cannabalising for valves, sturdily made and with an RF stage and a BFO. Do beware of the twin caveats of mains-transformerless ("AC/DC") power supply implementation and metal casework, though- there are various crucial insulating washers and strips to make the set safe and faults or incompetent previous owners could make it dangerous, so thorough insulation testing os important.
"Sturdy" it weighs a ton it looks un messed with as far as I can see.
Front glass and tuning scale are grubby it looks like all its valves are there
I haven't compared but some may be same as the Bush
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Old 24th May 2019, 8:37 pm   #5
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Default Re: Eddystone 840C

That does look in good nick, and the 840C was the final version of a series, it added a cunning linearising link in the tuning drive so that the scale was less cramped at the HF end. One thing in favour of Eddystones when it comes to overhaul is that components were usually just placed and "glued" in place with solder, rather than being thoroughly twisted around tags, making removal and replacement somewhat less of a tricky business.

It will certainly attract interest from others here if you decide it's not your cup of tea.
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Old 24th May 2019, 8:53 pm   #6
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Default Re: Eddystone 840C

I've got its elder sibling - an 840A - as my bedside radio. They work OK, but are let-down (at least for present-day amateur-HF listening) by the inevitable silly-number-of-KHz-per-turn-of-the-tuning-knob, and the 10KHz-or-so-wide IF response.

They're actually one of the easier Eddystones to restore: replace "that capacitor" and expect all the ceramic-bodied Erie resistors to have drifted wildly.

There are a couple of detailed restoration/refurbs of the 840A on the Eddystone User Group's website. The one by Gerry O'Hara is good.

The 840C isn't spectacularly different.

On mine, the 2-pin power-socket/mains-lead was long-lost, so I removed the 2-pin plug from the chassis, bored-out one of the holes in the Paxolin panel, and fitted a screw-up cable-gland along with a permanently-attached 2-core mains lead. At least that way you can go some way to make it more than a 50/50 chance the Neutral of the mains will be connected to the chassis.
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Old 24th May 2019, 9:02 pm   #7
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Default Re: Eddystone 840C

Is "that capacitor" C72?
I thought the original connector had an earth connection for the case so I wasn't going to try it without an earth.
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Old 24th May 2019, 9:10 pm   #8
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Default Re: Eddystone 840C

A lot of these are fitted with an IEC mains socket, a lot safer on a live chassis.
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Old 24th May 2019, 11:15 pm   #9
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Default Re: Eddystone 840C

C72 is indeed 'that' capacitor.
The earth connection is isolated from the 'live' chassis by C3.
I only ever run these type of receivers via an isolation transformer.
In the case of my 670A, I use two identical mains low voltage transformers back to back.
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Old 25th May 2019, 6:45 pm   #10
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Default Re: Eddystone 840C

Say I wanted to try power as it is I don't have a vairiac or an isolation transformer but I have 2 60w bulbs.
Any pre power preparations or is it not worth it and it will likely go bang big time?
Don't know anyone with a vairiac or isolation transformer.
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Old 25th May 2019, 6:48 pm   #11
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Default Re: Eddystone 840C

I have a Variac but a few miles away,anyway the offer is there as is my bench.Other than that your bulbs should help.Put on the power and unless they light up very bright ,give it 30 seconds or so and repeat getting longer each time.
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Old 25th May 2019, 7:10 pm   #12
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Default Re: Eddystone 840C

You're very far way away but thanks for the offer .
I checked the fuses earlier and they are both ok.
I don't think the guy it came from had the mains lead and hes had it well over 20 years.
2 bulbs in the live and introduce it to mains gently.
I did measure the resistance between live and neutral and I'm sure it was 200k ohms plus.
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Old 25th May 2019, 7:25 pm   #13
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Default Re: Eddystone 840C

I notice from your photos that it's got a couple of the Plessey electrolytics with red-and-black ends and a yellow label round the middle.

They're bypass-capacitors for the cathode-resistors on the UAF42 1st-audio and the UL41 audio power-output stage.

These capacitors are known to quietly transform themselves from being a capacitor to being a low-value resistor with a bit-of-capacitance as a side-order.

If the UL41's cathode-bypass capacitor (C73) goes leaky it means the valve will pass excess current and have a short/unhappy life.

Given the current cost of a new UL41 of reputable-origin - typically 18 - , it would to me make sense to replace these capacitors as well as "that capacitor" before powering-up.
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Old 25th May 2019, 8:03 pm   #14
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Default Re: Eddystone 840C

They're bypass-capacitors for the cathode-resistors on the UAF42 1st-audio and the UL41 audio power-output stage.
Thanks for the vital tip I won't put power to it till the Plessseys and "that capacitor" have been changed.
I'm a valve dummy I want to see it work if I'm lucky.
I normally fix cars
But I have done the RAE and had a licence for 20 years.
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Old 25th May 2019, 8:47 pm   #15
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Default Re: Eddystone 840C

How close to 25 uf do I need to be as I'm creating a list on CPC
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Old 25th May 2019, 9:10 pm   #16
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Default Re: Eddystone 840C

You won't get 25 now, 22 is the nearest modern value. Go for the same or higher voltage rating.
http://eddystoneusergroup.org.uk/Man...sed%202-10.pdf
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Old 25th May 2019, 10:16 pm   #17
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Default Re: Eddystone 840C

Thanks, I'm having problems translating old parts to modern parts c72 is I think a 10 nf 350v DC tubular ceramic, will any ceramic do like a brown disc one?
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Old 25th May 2019, 10:34 pm   #18
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Default Re: Eddystone 840C

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.

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Old 27th May 2019, 4:58 pm   #19
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Default Re: Eddystone 840C

Just to make sure I'm understanding the tangle of components and reading the circuit properly is this "that capacitor"?
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Old 27th May 2019, 5:01 pm   #20
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Default Re: Eddystone 840C

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.
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