Ekco AD76. Same capacitor keeps failing.

[Filament]

Many thanks to those who have taken the trouble to run this by the simulator. To clarify a little, I don't have the original rectifier as I acquired the set with a PV30 grafted onto a B5 base and presumably using just the half of what was a full wave job. It had gone soft anyway. The set is currently fitted with a CV1267 which is a 1D5 equivalent. I have since acquired a new 1D5 which is currently packed away in storage due to a pending house move as is my scope, if it still works. I may be able to borrow a scope, but in order to carry out any ripple observations, I will still need a suitable capacitor! So, I think I will try the recommended RS 8.2uf item. Thanks Herald 1360! I checked out the Jellyfish site too and will bear them in mind. Cheers, Ray.

[Filament]

Having just checked over a few things, I found that the dropper was set to 220-230 instead of the more appropriate 240-250. Although this only feeds the heater chain, I have now re-set it. Also, I find there is no 50 ohm resistor before the rectifier anode. The resistance reading I saw was 4.5 ohms between the anode and the mains pin and that was including the interference suppression coil. There is no evidence of this being the result of a "bodge" as apart from the strange rectifier and the replacement 8uf smoothing cap, the set is original. So from this, it appears that the set was made without the series resistor to the rectifier. Before I try another cap, I think I should at least add a resistor to the circuit. Any thoughts?

[beery]

Hi Fillament,
I would add in a 50 ohm resistor if you can't find one in the set, it should be a wirewound type. I'm not sure of the wattage, say at least 5W. The resistor will limit the ripple current, but it is there to limit the peak current in the rectifier as much as the smoothing capacitor.
The manual seems to show that R15 is located on tags on the mains input choke, but the photo isn't exactly clear. Maybe someone who has one of these sets can confirm?

Cheers
Andy

[buggies]

Originally Posted by beery

Hi Fillament,
The manual seems to show that R15 is located on tags on the mains input choke, but the photo isn't exactly clear.
Andy

I don't have one - but a couple of images on the web seem to confirm a green tubular component in that location.

[Filament]

I think I'm getting there! A rummage in the box revealed a large 100 ohm resistor which looks to be at least 5w, possibly a 10w item. Not knowing where it was mounted in any set that had it fitted in the factory, I noticed there was a link between pins 1 and 2 on the rectifier holder. I removed the link and mounted the resistor in its place so it was directly connected to the anode. I then wired in the new RS 10/450 smoothing cap and powered up the set. It was still performing well an hour later! I still have some issues like one of the mains suppessor caps missing. Again, the set does not appear to ever have one fitted, could this be a "Friday" radio? I will add one but thats a job for tomorrow. Strangely, the set now performs better with the aerial removed.

[crackle]

Check the capacitor can stays cool.
Mike

[murphyv310]

The absence of the 50ohm surge limiter will certainly not do the rectifier any favours one little bit. It will of course increase the ripple current. I'd think that now you need to fit another rectifier and the limiter resistor preferably a 47 or 50 ohm wirewound rated between 5 & 7 Watts. Replace the reservoir with the correct value or the nearest higher modern value and a peak voltage rating of 400v or 450v, no point of going above that as it won't ever get to even 400v. I'd still stick with an electrolytic as you have now found the issue plus the rectifier is now most likely to be damaged. The fact there was no resistor and when the valve shorted the cap would literally go bang in milliseconds. Bin the rectifier in the set as I'd put my pension on that it's failing when hot.

I understand you have had an hours running with the rectifier but TBH, I'd never even consider using a valve especially a rectifier that's been hammered like this one.

[Filament]

My exploding capacitor induced paranoia is starting to lift. The addition of the anode resistor seems to have done the trick. Last night, the set performed well for over 2 ½ hours! Still cautious, I will leave the value at 100 ohms, I feel it is kinder to the 85 year old to do so. The new 10/450 cap from RS did not seem unduly hot. The CV1267 rectifier was still working well but I changed it for a new 1D5 and put the CV1267 back in its box as being the resourceful type, I feel it is still of some use. I'm really looking forward to popping it back in its case now.

[beery]

Hi Filament,
That's great. Hopefully you can now put it back together and enjoy listening to it

Cheers
Andy

[murphyv310]

Well done.

A lesson for us all, check why a set behaves as it did.
TBH the original cap didn't explode without the rectifier missing its surge limiter so this is why I reckon the rectifier was breaking down suddenly, no doubt it did run cooler and the current drawn would be less with the addition of the 100 ohm surge resistor. I agree just leave the 100 ohm in the set.

Enjoy.

[ms660]

Some of the rectifiers for AC/DC receivers could be operated without any surge limiter, the UR1C and CY31 being examples if used with an 8uF reservoir capacitor.

Lawrence.