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Old 27th Feb 2017, 3:18 pm   #1
Voxophone
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Default Ekco A22 capacitor value

Hi all,

I’m currently restoring an Ekco A22 and seem to have an inconsistency in one of the capacitor values. The a.f. coupling capacitor to the EBL31 (Trader C24, manufacturer’s C30) is stated to be 0.05uF but my set has a 0.005uF component installed. Has anyone else come across the lower value in their own sets? There aren’t any obvious signs that it has been replaced in the past.

I realise it probably doesn’t matter a great deal but I’m re-stuffing the waxies on this set and probably won’t be able to change it again later on.

Cheers

Liam
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Old 27th Feb 2017, 4:41 pm   #2
crackle
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Default Re: Ekco A22 capacitor value

Sounds like human error when the set was assembled.

Mike
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Old 27th Feb 2017, 5:08 pm   #3
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Default Re: Ekco A22 capacitor value

I've come across values different to that stated on the schematic for a set on a few occasions but not by a factor of 10.
In this case though the reduction in value won't have any significant effect so I'm guessing it could be cost cutting, shortage of the correct value or human error as Mike suggests.
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Old 27th Feb 2017, 5:13 pm   #4
David G4EBT
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Default Re: Ekco A22 capacitor value

I've restored three and as found, they were all .05µF per the original Ekco Datasheet.

If you're stuffing the waxies, I guess you'll be stuffing the upright cathode bypass cap (25µF 25V). No great chore.

By far the nicest of the round Ekcos and the easiest to restore, with most components on the tag-board on outside of the rim of the chassis.

Good luck with the restoration Liam.
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Old 27th Feb 2017, 5:16 pm   #5
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Default Re: Ekco A22 capacitor value

Having had a look at the trader sheet I wold plump for the higher value, makes more sense for audio.
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Last edited by merlinmaxwell; 27th Feb 2017 at 5:17 pm. Reason: spelling
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Old 27th Feb 2017, 5:42 pm   #6
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Default Re: Ekco A22 capacitor value

Thanks all. I'll go for 0.05. Might have to find a narrower type to fit inside the tube. I agree the A22 is a nice set to work on. The round construction is very practical and not just for show. Fingers crossed the EBL31 is ok!

Cheers

Liam
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Old 27th Feb 2017, 5:43 pm   #7
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Default Re: Ekco A22 capacitor value

I would say that, considering the high input impedance of the output valve (many MOhms), going for the higher or lower value will have no significant effect on the audio quality. In either case the low frequency roll-off is going to be well below 20Hz.
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Old 27th Feb 2017, 6:18 pm   #8
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Default Re: Ekco A22 capacitor value

Quote:
I would say that, considering the high input impedance of the output valve (many MOhms)
There is the 1M volume pot to ground (ground ish anyway) 0.05 is 20Hz (not noticable) 0.005 200Hz (most noticable).
Quote:
Might have to find a narrower type to fit inside the tube
It has a low voltage across it, a slim 63V job will do admirably.
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Old 27th Feb 2017, 6:41 pm   #9
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Default Re: Ekco A22 capacitor value

Looks like the C30 I removed from mine is 0.05uF. Hard to see a decimal point, despite cleaning all the goo off.

Go carefully with component replacement. On my A22, found that a lot of internal fittings suffered from metal fatigue. I wasn't being too rough, but a few of the tag strip eyelets turned from closed O shape into open U shapes when de-soldering old component legs.
Also, some of the P clips holding the wiring loom around the outside of the chassis split in two when unscrewed.

Good Luck!

SR
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Old 27th Feb 2017, 6:48 pm   #10
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Default Re: Ekco A22 capacitor value

The manufacturers manual confirms it is indeed 0.05uF.
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Old 27th Feb 2017, 7:32 pm   #11
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Default Re: Ekco A22 capacitor value

Quote:
Originally Posted by merlinmaxwell View Post
Quote:
I would say that, considering the high input impedance of the output valve (many MOhms)
There is the 1M volume pot to ground (ground ish anyway) 0.05 is 20Hz (not noticable) 0.005 200Hz (most noticable).
Quote:
Might have to find a narrower type to fit inside the tube
It has a low voltage across it, a slim 63V job will do admirably.
That'll teach me to look at a schematic before posting! The 1M pot will indeed affect the low frequency roll off.

Anyway using the formula 1/2pi*R*C for the -3dB roll off frequency and substituting 1M (volume pot) for R gives:

32Hz for a value of 0.005uF for C24 and 3.2Hz for a value of 0.05uF. Both should be acceptable in this radio I would have thought.
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Old 27th Feb 2017, 8:10 pm   #12
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Default Re: Ekco A22 capacitor value

I used an online time constant calculator and did the reciprocal, near enough IF the calculator or my inputs where 10X out, which seems to be the case here. OOPS
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Old 27th Feb 2017, 9:16 pm   #13
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Default Re: Ekco A22 capacitor value

I do not think the fittings were damaged by fatique. Much more likely to be season cracking.
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Old 5th Mar 2017, 6:05 pm   #14
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Default Re: Ekco A22 capacitor value

A quick followup question on the A22. Does anyone know how to remove the switched volume pot on this set?

The switch on mine measures o/c and I'd like to try opening it.

Do I need to unscrew the fastening around the spindle shown in the attached photo? I don't really want to force it till I know for certain.
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Old 5th Mar 2017, 6:18 pm   #15
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Default Re: Ekco A22 capacitor value

Yes that is the fixing nut , try a bit of heat on it if it is stuck , Mick.
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Old 5th Mar 2017, 7:06 pm   #16
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Default Re: Ekco A22 capacitor value

OC measured mains switches often respond to (with the thing plugged in) a few cycles of on/off. This burns off the oxide layer.
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Old 5th Mar 2017, 7:55 pm   #17
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Default Re: Ekco A22 capacitor value

I love my A22, but wish the audio sounded better, it sounds very flat.
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Old 6th Mar 2017, 4:33 am   #18
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Default Re: Ekco A22 capacitor value

What? You haven't got surROUND sound?

Lack of top, no treble, could be low HT if you have checked everything else.
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Old 6th Mar 2017, 11:45 am   #19
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Default Re: Ekco A22 capacitor value

Quote:
Originally Posted by merlinmaxwell View Post
OC measured mains switches often respond to (with the thing plugged in) a few cycles of on/off. This burns off the oxide layer.
Thanks. I'll give it a go and see how it works out. I'm pretty close to powering up now. Just need a couple more caps and the top connector re-glueing on the EBL31.

Liam
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Old 6th Mar 2017, 3:08 pm   #20
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Default Re: Ekco A22 capacitor value

Do it with the valves out (saves the poor heaters), leave the pilot lamp in for indication.
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