wayne
Society Members
Posts: 138
|
Post by wayne on May 17, 2021 16:38:50 GMT 12
How do I add a photo ?
|
|
wayne
Society Members
Posts: 138
|
Post by wayne on May 17, 2021 16:39:56 GMT 12
Sorry 3 of those capacitors of the same value
|
|
wayne
Society Members
Posts: 138
|
Post by wayne on May 17, 2021 17:00:28 GMT 12
set multi meter to AC with radio on negative probe to negative side of capacitor positive probe to positive side of capacitor, note the reading ?
|
|
|
Post by Peter Walsham on May 17, 2021 17:05:35 GMT 12
If you connect your multimeter (switched to DC Volts) - black meter lead to the capacitor -ve terminal & the red meter wire to the capacitor +ve terminal (one capacitor at a time) and switch the radio on. Note down the voltage you read, then turn the radio off & disconnect the multimeter and connect its leads to the other capacitor. Turn the radio on, and note down that voltage reading. At this stage, leave the radio 'powered up' for as little time as you can, and keep an eye on the 5Y3 valve for signs of 'distress' (internal sparking).
I'm not sure how to ad a photo to a post, but if you post one, you can then edit the post and add a photo - top RH corner of the 'edit' text box, where it says 'Add Attachment', then click on 'Save Changes' in the bottom RH corner of the text box.
|
|
wayne
Society Members
Posts: 138
|
Post by wayne on May 17, 2021 17:17:29 GMT 12
one more question should I try and connect the leads then turn the radio on or turn the radio on and hold the leads in place by hand ?
will wait for your reply then must log off for now and get dinner cooked kind regards Brian
|
|
wayne
Society Members
Posts: 138
|
Post by wayne on May 17, 2021 17:19:22 GMT 12
sorry I signed off as Brian should be Wayne
|
|
|
Post by Peter Walsham on May 17, 2021 17:35:02 GMT 12
Ha ha - No problem. I did read your first message which explained the name.
It would be a good idea if you could make the meter connections using alligator clips or jumper leads.
I meant to add - watch out for those electrolytic capacitors, as they can store a charge of electricity (at high voltage) for a long time after the power has been switched off. This particularly applies to a radio where the speaker has been unplugged from the chassis. The first filter capacitor can charge up to 450 or more volts, and can & will 'bite' you if you let your guard down. One easy way to prevent this is to 'clip' a 10k Ohm resistor across each capacitor after the radio has been unplugged from the power. This resistor 'discharges' the 'charge' in the capacitors really quickly (in a couple of seconds). The second filter capacitor is often discharged by the chassis circuit - but don't count on it. It's always a good idea to measure the HT (otherwise known as the B+) voltage before poking your fingers inside a chassis.
|
|
peter
Tinkerer
Retired, collector of vintage radios and test equipment for restoration and repair.
Posts: 97
|
Post by peter on May 18, 2021 0:06:32 GMT 12
if the 5Y3 is getting excessively hot this indicates a low resistance in the rest of the circuit - this can be the capacitors in the power supply filter breaking down (google pi filter for more info) or something else after the power supply. Useful devices to help you track this down are indescant 100 or 200w light limiters. What I would do initially is replace the caps in the pi filter and disconnect the rest of the ht line after the 5Y3 and pi filter from there on. if that results in OK ht voltages measured on your multimeter AFTER the caps and valve (use the highest DC range), then I'd check the disconnected side after the mains filter caps and 5Y3 valve to earth (do disconnect any power first though) with the ohms range of your meter. if that checks out OK (usually well above 1k) then Id reconnect it to the power supply, take out ALL the valves after the 5y3 and see what happens when you power on. If the valve starts to get hot with only it in you have a low resistance somewhere. The simplest solution is probably to replace all the paper and electrolytic caps in the circuit and try again. If still getting hot then you have a dicky resistor and my money would be the ones on the valve anode side they often seem to cook up and go high.
If your 5Y# does NOT get hot with the other valves removed then I'd put in the other valve bar one (jumper the heater connections just in case they are in series) and progressively swap them out seeing if things get hot with a particular valve in place. If they do try a replacement valve for that one.
The above won't find all possible faults but gives you a place to start. The main idea is effectively progressively disconnecting parts of the radio then reconnecting bit by bit until the fault reappears in a specific section. Good luck.
|
|
wayne
Society Members
Posts: 138
|
Post by wayne on May 18, 2021 14:04:01 GMT 12
Hi Peter I followed your instructions and got the following, there are 3 capacitors 1 8uf voltage reading 206 2 which should be 16uf but 8uf at the moment which is reading 117V 3 8uf reading 103V I turned it off straight away so didnt look at the valve Thanks for your last message to be honest at the moment most of that is out of knowledge. Regards Wayne
|
|
wayne
Society Members
Posts: 138
|
Post by wayne on May 18, 2021 14:06:35 GMT 12
I should add that I have replaced all of the wax paper capacitors that I am aware of and the 3 that I spoke of in the last message are new as well
|
|
wayne
Society Members
Posts: 138
|
Post by wayne on May 18, 2021 14:36:07 GMT 12
I have just found what I think is a capacitor marked with the following 0.02uf DC working 500V at 70 deg 350V at 100 deg I have 0.02 630 V capacitors should I replace it ?
|
|
|
Post by Peter Walsham on May 18, 2021 15:21:26 GMT 12
Hi Wayne
That last message was from another Peter, not me.
Those voltage readings are very low, and suggest that there is some sort of a high load on the H.T. circuit, therefore no wonder the poor 5Y3 is getting rather hot. Do you know what that 0.02uF capacitor is connected to?. Is it an old wax one? I would certainly try replacing it anyway, and carry out those two voltage checks again, and let us know whether they're any different.
|
|
wayne
Society Members
Posts: 138
|
Post by wayne on May 18, 2021 15:46:26 GMT 12
Ive taken it off its silver in colour marked Visconel.X Metalmite typ cp345 and it is red on one end and black on the other end. the wire coming off the red end has black insulation on it so I dont think the .022 capacitor I have is the right one. The black end is connected to another valve socket the other end goes to in my eyes lots of places
|
|
wayne
Society Members
Posts: 138
|
Post by wayne on May 18, 2021 15:51:32 GMT 12
Two heavier insulated wires come from what I believe is the transformer directly to the 5y3 valve socket if that helps make things clearer
|
|
|
Post by Peter Walsham on May 18, 2021 16:34:37 GMT 12
There will be 4 wires coming from the transformer to the 5Y3. There will be 5 Volts between the two wires that connect to pins 2 & 8, and 700 (odd) Volts between pins 4 & 6.
If the capacitor that you have removed says that it's a 0.02uF, then the new one you have will be OK to replace it. You could try testing the old one on the 'Ohms' range on your multimeter, and see what sort of a reading you get - although this might not tell us very much. Does your multimeter have a capacitor test function on it?. I prefer to use an analogue meter for initial basic capacitor testing.
How far from Pukekohe do you live, as I would be more than happy to help you with fault finding on this chassis - if you can get it to me?
Peter
|
|