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Vintage Radio (domestic) Domestic vintage radio (wireless) receivers only. |
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19th Jan 2023, 8:45 pm | #1 |
Tetrode
Join Date: Sep 2021
Location: Findhorn, Moray, Scotland, UK.
Posts: 66
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Ekco U76 Radio
I have just acquired one of these rather stylish (IMHO) valve radios.
I think it's going to need a recap at nearly 75 years of age. While I'm waiting for it to arrive does anyone have a list of capacitor values with voltages so I can get an order in? I have the Trader Service Sheet, but that only lists the values and not the voltages. Does anyone have any particular advice for working on one of these? Is it worth trying to reform the electrolytic filter capacitor? Thanks, |
19th Jan 2023, 10:08 pm | #2 |
Octode
Join Date: Apr 2005
Location: Peterborough, Cambridgeshire, UK.
Posts: 1,897
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Re: Ekco U76 Radio
If the capacitor is a dual can Reservoir smoother and looks in good condition without corrosion or leakage on the seal end I would try reforming it. Then once the set is working monitor the can temperature. Replacement for the wax capacitors should be rated at 400v or 630V if they are available at the same price. The BVWS to a good range most are 630V.
Rich |
19th Jan 2023, 10:27 pm | #3 |
Nonode
Join Date: Oct 2017
Location: Bristol, UK.
Posts: 2,368
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Re: Ekco U76 Radio
It's a live chassis radio so be careful. Ideally use a mains isolation transformer but if you don't have one make sure that the chassis is connected to mains neutral and not live. The best way to work out capacitor voltage ratings is to look at the Trader Sheet for the max smoothed HT voltage, which in this case is the grid2 voltage on V4, UL41, 163v. The voltage at the cathode of the rectifier will be higher but that only affects the voltage rating of the main electrolytic. You then need to add a bit of margin since it is not wise to run caps at their max rated voltage. For the wax paper capacitors with values between 0.001uF and 0.1uF a working voltage of 250v is the bare minimum but probably sensible to go for 400v. You can use 630v components if these are cheaper and more readily available. One to watch is C31 (0.0025uF) the tone corrector where signal conditions can result in high AC voltages so for this use a 630v component. You'll also find that you can't always get an exact replacement but the tolerances on the old capacitors were such that a "preferred value" that is as close as possible to the quoted circuit value will be fine (e.g. 0.0022uF for C31). Don't mess with any capacitors that are either lower in value than 0.001uF or even above if they are silvered mica or ceramic types - they rarely fail so leave them as found. The date of this set is circa 1948 so it is worth trying to reform the main electrolytics. Earlier caps are less likely to resuscitate. For the V4 cathode (8v according to the Trader Sheet) decoupler C30 (50uF) then use a 47uF rated between 25v and 63v. Jerry
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19th Jan 2023, 10:42 pm | #4 |
Tetrode
Join Date: Sep 2021
Location: Findhorn, Moray, Scotland, UK.
Posts: 66
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Re: Ekco U76 Radio
Hi,
I'm aware it's a live chassis design and I do have an isolation transformer. Yes, I was planning on leaving any ceramic or mica caps in place and I know that capacitor values have 'rationalised' over the years, but thanks for the rest of the advice, very helpful. OK, I will give reforming the electrolytic a go if it's in good physical shape, haven't had much success in the past, but I can now borrow a variac and bring things up a bit more slowly than I could with a dim bulb tester. Thanks, |
19th Jan 2023, 10:43 pm | #5 | |
Tetrode
Join Date: Sep 2021
Location: Findhorn, Moray, Scotland, UK.
Posts: 66
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Re: Ekco U76 Radio
Quote:
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27th Jan 2023, 10:51 pm | #6 |
Triode
Join Date: Feb 2016
Location: Fife, Scotland, UK.
Posts: 30
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Re: Ekco U76 Radio
No particular advice, but I agree entirely its a stylish radio. The only radio on my collection that my wife doesn't complain about being on display in the sitting room. If I had to dispose of my collection it would be the last to go.
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28th Jan 2023, 9:16 pm | #7 | |
Tetrode
Join Date: Sep 2021
Location: Findhorn, Moray, Scotland, UK.
Posts: 66
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Re: Ekco U76 Radio
Quote:
It has finally arrived, the case is in very good order, it will only need a polish to make it look like new. The chassis was taken out by someone quite some time ago by the look of it, no work seems to have been done, but it was not secure. The back panel is a rather warped, while there is no rust on the chassis it must have been stored somewhere damp. I will try some steam, then some PVA and water and if those don't work I will mount it on some 2mm fiber board. |
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