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Old 10th Jun 2022, 10:06 am   #1
Davidwkd71
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Default Eddystone 840C

Eddystone 840 c all works perfect do I leave as is or replace some capacitors 🤔
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Old 10th Jun 2022, 10:18 am   #2
Chris G0EYO
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Default Re: Eddyston 840 c

If you haven't found it already look up the Eddystone User Group website. eddystoneusergroup.org.uk. It is a mine of information for Eddystone Enthusiasts. There is also the Eddystone User Group.io forum which is worth joining.
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Old 10th Jun 2022, 10:20 am   #3
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Default Re: Eddyston 840 c

Normal advice would be to swap out all the Hunts. As a minimum change grid coupling cap on output valve as a precaution and enjoy

I had an 840C and didn't have to do much to it other than a realignment.
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Old 10th Jun 2022, 11:00 am   #4
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Default Re: Eddyston 840 c

I'll fix the typo in the title, then people using search can find this thread....

It's worth taking extra care over titles. Your thread will show if someone clicks 'New posts' but if they later remember it and want to find it again, an error in the title can prevent it showing in a search. It can make a big difference to the response you get.

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Old 10th Jun 2022, 2:11 pm   #5
Davidwkd71
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Default Re: Eddyston 840 c

Quote:
Originally Posted by wd40addict View Post
Normal advice would be to swap out all the Hunts. As a minimum change grid coupling cap on output valve as a precaution and enjoy

I had an 840C and didn't have to do much to it other than a realignment.
Thanks wd40addict
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Old 10th Jun 2022, 3:54 pm   #6
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Default Re: Eddystone 840C

Yes, swap out anything Hunts; the grey plastic capacitor at rhe top of your photo and the black one at the bottom I would consider suspicious irrespective of manufacturer.

I've got an 840A s my bedside-radio [I'm an insomniac and listening to Radio China's strange rants lulls me to sleep] - the one thing to watch out for in these radios is small deeply-embedded capacitors used to decouple the AGC line: they're about 3/4 inch long, wire-ended, brown, round-ended - hence the colloquial nickname "Rat-droppings". They go leaky and the last thing you really want is a couple of capacitors-pretending-to-be-1-Megohm-resistors shunting the AGC-line to ground.

Also, bearing in mind that it's an AC/DC radio, check the low-value capacitor wired in parallel to the rectifier; if this has gone open-circuit it can cause horrible issues with 'modulation hum' when listening to double-sideband-full-carrier AM stations. Replace with a modern 1Kv-rated 0.01uF ceramic....
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Old 10th Jun 2022, 6:50 pm   #7
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Default Re: Eddystone 840C

The pale brown cylindrical capacitors and the similar-looking but smaller red ones are tubular ceramic types and are generally very reliable. The fatter yellowish one in the centre left of the picture looks like a Mullard C296 (colloqiually "mustard") type, these are famously reliable. However the black 0.1uF 600V Hunts shown is another matter, likely to be electrically leaky, a failing not helped by the tendency of the casing to develop fine cracks, allowing the insides to deteriorate. Also, the small pale blue one on the tagstrip could be a paper type, it won't cost a fortune to replace if in doubt. The resistors look like basic carbon composition types and could well have drifted off value, particularly high resistance ones like the 2.2 Megohm ones shown. However, if the radio seems to be working well, then treat checking the resistors as an "at leisure" rather than "urgent" matter, straightforward valve circuitry like this is notably tolerant of a bit of resistance value drift.
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Old 10th Jun 2022, 7:56 pm   #8
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Default Re: Eddystone 840C

Quote:
Originally Posted by turretslug View Post
The pale brown cylindrical capacitors and the similar-looking but smaller red ones are tubular ceramic types and are generally very reliable. The fatter yellowish one in the centre left of the picture looks like a Mullard C296 (colloqiually "mustard") type, these are famously reliable. However the black 0.1uF 600V Hunts shown is another matter, likely to be electrically leaky, a failing not helped by the tendency of the casing to develop fine cracks, allowing the insides to deteriorate. Also, the small pale blue one on the tagstrip could be a paper type, it won't cost a fortune to replace if in doubt. The resistors look like basic carbon composition types and could well have drifted off value, particularly high resistance ones like the 2.2 Megohm ones shown. However, if the radio seems to be working well, then treat checking the resistors as an "at leisure" rather than "urgent" matter, straightforward valve circuitry like this is notably tolerant of a bit of resistance value drift.
Yes that black one 0.2 if I'm looking to replace with a modern equivalent.
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Old 11th Jun 2022, 5:07 pm   #9
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Default Re: Eddystone 840C

That's a good move - capacitor-technology has moved on a lot in the 50-decades since your 840C was built.

Reworked, to eliminate the drifty-resistors and leaky-capacitors, the Eddystone 840x radios can be fun. OK, they've only got 4 IF tuned-circuits so they will never beat the likes of an AR88 when it comes to listening to amateur SSB stations... and the way they shift half-a-Kilohertz when you adjust the RF-Gain control is annoying - but they're really fun receivers to play with.

And they have a good built-in loudspeaker - so they're fun to go listening on the 6.1-6.3MHz sunday-morning free-radio channels! so you can re-create the 'fiddly tuning' memories of the 1960s pirate-stations.
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Old 23rd Jun 2022, 9:31 am   #10
Davidwkd71
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Default Re: Eddystone 840C

Quote:
Originally Posted by turretslug View Post
The pale brown cylindrical capacitors and the similar-looking but smaller red ones are tubular ceramic types and are generally very reliable. The fatter yellowish one in the centre left of the picture looks like a Mullard C296 (colloqiually "mustard") type, these are famously reliable. However the black 0.1uF 600V Hunts shown is another matter, likely to be electrically leaky, a failing not helped by the tendency of the casing to develop fine cracks, allowing the insides to deteriorate. Also, the small pale blue one on the tagstrip could be a paper type, it won't cost a fortune to replace if in doubt. The resistors look like basic carbon composition types and could well have drifted off value, particularly high resistance ones like the 2.2 Megohm ones shown. However, if the radio seems to be working well, then treat checking the resistors as an "at leisure" rather than "urgent" matter, straightforward valve circuitry like this is notably tolerant of a bit of resistance value drift.
Yes thst pale blue one im trying to find out what it is on my diagrahm but its not showing up any where its got a o.1 uf 200 dc stamped on it as to what it is im a bit snookered.
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Old 23rd Jun 2022, 11:06 am   #11
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Default Re: Eddystone 840C

That one is connected between the junction of the 2x 2.2 Megohm resistors in series with the magic eye grid and chassis, it filters the DC from demodulating the carrier so as to prevent the eye fluttering too much and also guard against any hum coupling from the internal capacitance of the directly-heated eye. I don't have a circuit to hand, but it may not even be on some versions of the circuit, it's the sort of thing that could be a production revision. It won't cost much to replace it with a 0.1uF 200 or 250VDC component while the set is opened up.
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Old 24th Jun 2022, 10:12 pm   #12
Davidwkd71
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Default Re: Eddystone 840C

Quote:
Originally Posted by turretslug View Post
That one is connected between the junction of the 2x 2.2 Megohm resistors in series with the magic eye grid and chassis, it filters the DC from demodulating the carrier so as to prevent the eye fluttering too much and also guard against any hum coupling from the internal capacitance of the directly-heated eye. I don't have a circuit to hand, but it may not even be on some versions of the circuit, it's the sort of thing that could be a production revision. It won't cost much to replace it with a 0.1uF 200 or 250VDC component while the set is opened up.

One on order going to change it. Thanks for that information
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