Can't get radio to work after cap replacement - UK Vintage Radio Repair and Restoration Discussion Forum

teedeeb · 14th Sep 2017, 11:28 pm

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:

The "fuse lamp" above the main transformer does not work. When looking closely however I can see the wire inside is not broken. What does this mean?
I noticed resistor R3 has a broken wire. I'll fix that tomorrow, but I can't imagine that would be the reason behind the radio not working.
I measured voltage over smoothing capacitors C47 and C48. One starts out at 300-310V at start, and a few seconds later drops to ~255V. The other one starts at 330V and drops after a few seconds to 290V. Is this normal? Are these voltages in the range of what you'd expect internally?

Any help would be greatly appreciated

paulsherwin · 15th Sep 2017, 12:02 am

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.

Boater Sam · 15th Sep 2017, 8:19 am

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?

TrevorG3VLF · 15th Sep 2017, 10:07 am

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.

Cobaltblue · 15th Sep 2017, 10:25 am

Quote:

Originally Posted by teedeeb

I've noticed the following things:[LIST][*]The "fuse lamp" above the main transformer does not work.

I would not expect the fuse bulb to do too much is a 300mA bulb and it probably has around a fifth of that flowing through it you should consider it a fuse not a bulb.

You should check it for continuity though using a meter or even a 6 V battery.

Cheers

Mike T

teedeeb · 16th Sep 2017, 10:13 am

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?

Sideband · 16th Sep 2017, 4:03 pm

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.

Boater Sam · 16th Sep 2017, 5:06 pm

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.

David G4EBT · 16th Sep 2017, 5:54 pm

Quote:

Originally Posted by teedeeb

Thank you for the comments.
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?

You may find that a 'ribbon' indoor aerial will be quite adequate. It's all that I use, pinned under a bookshelf out of sight. Google 'FM Indoor Ribbon Antenna' and you'll see lots of listings on e-bay - certainly in the UK. Expect to pay 3.00 - 5.00 Euro. (A UK listing - almost 300 sold - £2.85 GBP post free). They usually have a TV type coax plug on the end, but if your radio has two screw terminals, just cut the plug off and strip the two wires.

Hope that helps a bit.

ms660 · 16th Sep 2017, 6:34 pm

AM ?

Lawrence.

David G4EBT · 16th Sep 2017, 7:09 pm

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.

14th Sep 2017, 11:28 pm	#1
teedeeb Retired Dormant Member Join Date: Aug 2017 Location: Bruges, Belgium Posts: 6	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: The "fuse lamp" above the main transformer does not work. When looking closely however I can see the wire inside is not broken. What does this mean? I noticed resistor R3 has a broken wire. I'll fix that tomorrow, but I can't imagine that would be the reason behind the radio not working. I measured voltage over smoothing capacitors C47 and C48. One starts out at 300-310V at start, and a few seconds later drops to ~255V. The other one starts at 330V and drops after a few seconds to 290V. Is this normal? Are these voltages in the range of what you'd expect internally? Any help would be greatly appreciated

15th Sep 2017, 12:02 am	#2
paulsherwin Moderator Join Date: Jun 2003 Location: Oxford, UK Posts: 27,934	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.

15th Sep 2017, 8:19 am	#3
Boater Sam Banned Join Date: Dec 2013 Location: Middlewich, Cheshire, UK. & Winter in the Philippines. Posts: 3,897	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
TrevorG3VLF Rest in Peace Join Date: Apr 2011 Location: Matlock, Derbyshire, UK. Posts: 1,378	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.

16th Sep 2017, 10:13 am	#6
teedeeb Retired Dormant Member Join Date: Aug 2017 Location: Bruges, Belgium Posts: 6	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
Sideband Dekatron Join Date: Oct 2003 Location: Croydon, Surrey, UK. Posts: 7,567	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. __________________ There are lots of brilliant keyboard players and then there is Rick Wakeman.....

16th Sep 2017, 5:06 pm	#8
Boater Sam Banned Join Date: Dec 2013 Location: Middlewich, Cheshire, UK. & Winter in the Philippines. Posts: 3,897	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.

16th Sep 2017, 6:34 pm	#10
ms660 Dekatron Join Date: Apr 2011 Location: Cornwall, UK. Posts: 13,454	Re: Can't get radio to work after cap replacement AM ? Lawrence.

16th Sep 2017, 7:09 pm	#11
David G4EBT Dekatron Join Date: Feb 2003 Location: Cottingham, East Yorkshire, UK. Posts: 5,760	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. __________________ David. BVWS Member. G-QRP Club member 1339.