wayne
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Post by wayne on May 17, 2021 12:19:38 GMT 12
Hi all, very new to this so any help would be appreciated I have a Courier 7 valve radio I am attempting to get up and running. I think I have replaced all of the caps except a 16mfd 450 V. I believe all of the valves are good. It was going and I left the room for awhile came back to complete silence and by chance found one of the valves very hot to touch so turned it off Could it be the capacitor that I havent replaced yet? Im trying to learn how to test them but my Multimeter doesnt have a separate omhs range. I took it out and making sure I checked pos and neg I tested it on the omhs auto setting and got a reading of 5.20 and it slowly climbed up I stopped at 8.50
Thanks in advance Wayne
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Post by Peter Walsham on May 17, 2021 12:53:40 GMT 12
Hi Wayne
Which of the valves was getting too hot? Was that capacitor hot as well?
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Post by Peter Walsham on May 17, 2021 12:54:17 GMT 12
Hi Wayne
Which of the valves was getting too hot? Was that capacitor hot as well?
Peter
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wayne
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Post by wayne on May 17, 2021 13:20:49 GMT 12
Hi Peter Thanks for your reply The valve is 5Y3 GT I dont know if the capacitor got hot
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wayne
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Post by wayne on May 17, 2021 13:28:02 GMT 12
I have had a look and it appears that there is wiring that makes it back to a socket marked as speaker could it be that the capacitor is bad and causing no sound ?
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Post by Peter Walsham on May 17, 2021 13:36:31 GMT 12
Yes, it is very possible (and quite likely) that that 16uF capacitor has shorted. What I would do is to disconnect it, and check it for leakage resistance. It is almost imperative that high voltage electrolytic filter capacitors be replaced without question, as they cause so many problems - the worst one is a power transformer burn out, and this can happen real quickly.
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wayne
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Post by wayne on May 17, 2021 14:40:48 GMT 12
Yes I have taken it out and will replace it with a 20uf I dont know how to test it yet as my multi meter doesnt have a omhs setting you can change it has a auto setting and the reading I got started at around five and slowly went up thanks
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Post by Peter Walsham on May 17, 2021 15:00:25 GMT 12
That is a very basic test. My 'Auto Ranging' DMM (digital multimeter) (on its 'Ohms' range) has a potential of 100mV across the probes. That old filter capacitor may show up as being 'OK' at that low voltage, but with 250 (or more) Volts across it, the capacitor may be breaking down. Old electrolytics can do 'dumb' things. Ordinarily, I would connect a capacitor like that up to a power supply of about 250 Volts, with a series connected resistor of about 47k ohms, and measure the voltage across the capacitor, but you may not have a separate HV power supply you can try this on. A good capacitor (or one that isn't leaky, but could still be open circuit) will allow the full HT voltage to appear across the capacitor after a short time. This isn't a definitive test of filter capacitors, but will prove whether one is (electrically) leaky or not.
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wayne
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Post by wayne on May 17, 2021 15:18:37 GMT 12
I am learning as I go and some of that I dont understand yet I tested a new 8uf 500 v on my tester with O.L mohms showing and it went straight to 000 then straight back to 0.L I will obviously replace the one in question and go from there As you say just replace them anyway
Im waiting for an order Ive made for spares
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Post by Peter Walsham on May 17, 2021 15:29:28 GMT 12
Put that 8uF capacitor in to the radio, and see what the radio does. The fact that it's half the value of the old capacitor won't matter for the time being. If you have another of those, you could connect two of them in parallel.
I have been 'playing around' with valve radios & amplifiers for more than 50 years, and I am still learning new things.
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wayne
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Post by wayne on May 17, 2021 15:38:50 GMT 12
I will try that and let you know Thanks
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wayne
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Post by wayne on May 17, 2021 16:22:28 GMT 12
turned it on got a low hum which went away but still no sound and the same valve got hot but not the new capacitor
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wayne
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Post by wayne on May 17, 2021 16:25:57 GMT 12
Low hum came back which wasnt there before this problem
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Post by Peter Walsham on May 17, 2021 16:26:09 GMT 12
With the radio turned on, could you measure the voltage across both of the high voltage electrolytic capacitors? Try to do this relatively quickly, as it appears as though the 5Y3 valve might be under stress
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wayne
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Post by wayne on May 17, 2021 16:36:52 GMT 12
I dont have the knowlodge yet to know how to do this so will try and figure it out there are 2 capacitors there one I have replaced earlier 8uf 500V and the one I have just replaced of the same value which should be the 16uf
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