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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets. |
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14th Sep 2017, 11:28 pm | #1 |
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Can't get radio to work after cap replacement
Earlier, I asked for advice regarding which caps to replace in this thread for a Radiobell Scherzo radio (schematics here).
I have replaced a burst capacitor and the output coupling capacitor (C53 and C38 on schematics). After doing so, I've slowly powered up the radio using a variac by going from 110V to 220V in about 1hour, slowly. A few lamps are working at 6.3V. All of the tubes start to light up. Unfortunately, no sound, even no hum. I've noticed the following things:
Any help would be greatly appreciated |
15th Sep 2017, 12:02 am | #2 |
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Re: Can't get radio to work after cap replacement
The voltages are plausible and suggest that the valves are drawing current after the heaters have warmed up. You should be hearing something from the speaker, if only a faint hum. Check that the speaker is connected correctly and that the voice coil isn't open circuit. If there is no fault there, check the voltages at the output valve anode and cathode.
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15th Sep 2017, 8:19 am | #3 |
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Re: Can't get radio to work after cap replacement
Did it work before you changed any parts? Is there a switch or screw plug that disconnects the internal speaker when an extension speaker is used?
Is there a broken wire to the speaker? |
15th Sep 2017, 10:07 am | #4 |
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Re: Can't get radio to work after cap replacement
R3 discharges the AGC line, if this is open circuit, then the AGC line could go down sufficiently to cut off the radio.
Measure the voltages on all the valves. You will not get it to work until the volts are right. |
15th Sep 2017, 10:25 am | #5 | |
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Re: Can't get radio to work after cap replacement
Quote:
You should check it for continuity though using a meter or even a 6 V battery. Cheers Mike T
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Invisible airwaves crackle with life or at least they used to Mike T BVWS member. www.cossor.co.uk Last edited by Cobaltblue; 15th Sep 2017 at 10:27 am. Reason: addition |
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16th Sep 2017, 10:13 am | #6 |
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Re: Can't get radio to work after cap replacement
Thank you for the comments.
Meanwhile, I've replaced the broken resistor and flipped a switch on the back, and I'm making progress. I completely overlooked that switch to turn on or off the external speaker when testing for the first time... There's always a hum, and crackling noise when I change the frequency, but no recognizable reception. There's a possiblity to connect an external antenna. Would it be possible that there's no internal antenna and I absolutely need an external one? Where can I find an antenna like that nowadays? Last edited by teedeeb; 16th Sep 2017 at 10:26 am. |
16th Sep 2017, 4:03 pm | #7 |
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Re: Can't get radio to work after cap replacement
You will need an external aerial....this was made in the days before ferrite aerials! Nothing special, all you need is a few metres of wire in the aerial socket. Just find a piece of flex and bare the insulation for a few centimetres, push it in to the aerial socket and it should be more than enough to receive strong stations.
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16th Sep 2017, 5:06 pm | #8 |
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Re: Can't get radio to work after cap replacement
Is the crackling noise when you turn the tuning capacitor? If so, it sounds as though the fixed and moving vanes are ether shorting or have dirt between them.
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16th Sep 2017, 5:54 pm | #9 | |
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Re: Can't get radio to work after cap replacement
Quote:
Hope that helps a bit.
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16th Sep 2017, 6:34 pm | #10 |
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Re: Can't get radio to work after cap replacement
AM ?
Lawrence. |
16th Sep 2017, 7:09 pm | #11 |
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Re: Can't get radio to work after cap replacement
Oops - I lost plot there Lawrence!
Just 5 Metres of wire draped on the floor then should at least bring some stations in to at least show if the rado is working.
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