Ferguson 450, capacitor query. - UK Vintage Radio Repair and Restoration Discussion Forum

longneck90 · 11th Jan 2018, 6:02 pm

Hello to everyone, I recently rewound mains transformer for this radio, as original voltage seemed too low. When I asked it to produce music and the other stuff that radios receive, the result was violent whistling, and as the radio was tuned nearer to the received station, the output was mostly unintelligable. Ie. badly distorted. Eventually, I discovered, that, by attaching an 0.01 uf capacitor, between Pin 5, V3, and earth, reception improved dramatically, though a tiny bit 'wolly'. When I re-aligned the Intermediate Frequencies (IFs) Reception was perfect. What I only now notice, is that, I had replaced C14, which is between the Anode of Valve 2, and Pin 5 of Valve 3... and, that this capacitor is supposed to be 100 pf. The voltage at the Anode of V2 is 250 Volts, yet, I cannot find a 100 uf capacitor with a rating of more than 100 volts. Therefore, I was wondering why the radio works well when I have a 0.01 uf capacitor connected between Pin 3, V2 and earth, and is there some mistake about a capacitor of 100 pf, rating of 100 volts, situated between Pin 3, 250 Volts, and Pin 5 V3. Even though the radio is working well now, it is obviously not the way it was intended to work. (according to circuit diagram) I would be grateful for any information or advice regarding this particular problem, and maybe pointers to a way around it. All the best. John.

crackle · 11th Jan 2018, 6:15 pm

Ebay have 100pf high voltage capacitors. Search for; 10pF- 10nF 1/2/3 KV High Voltage/HV Ceramic Disc Capacitors
Could the violent whistling and distortion have been caused by instability as a result of bad screening of valves.

Mike

ms660 · 11th Jan 2018, 6:22 pm

Quote:

Originally Posted by longneck90

Hello to everyone, I recently rewound mains transformer for this radio, as original voltage seemed too low. When I asked it to produce music and the other stuff that radios receive, the result was violent whistling, and as the radio was tuned nearer to the received station, the output was mostly unintelligable. Ie. badly distorted. Eventually, I discovered, that, by attaching an 0.01 uf capacitor, between Pin 5, V3, and earth, reception improved dramatically, though a tiny bit 'wolly'. When I re-aligned the Intermediate Frequencies (IFs) Reception was perfect. What I only now notice, is that, I had replaced C14, which is between the Anode of Valve 2, and Pin 5 of Valve 3... and, that this capacitor is supposed to be 100 pf. The voltage at the Anode of V2 is 250 Volts, yet, I cannot find a 100 uf capacitor with a rating of more than 100 volts. Therefore, I was wondering why the radio works well when I have a 0.01 uf capacitor connected between Pin 3, V2 and earth, and is there some mistake about a capacitor of 100 pf, rating of 100 volts, situated between Pin 3, 250 Volts, and Pin 5 V3. Even though the radio is working well now, it is obviously not the way it was intended to work. (according to circuit diagram) I would be grateful for any information or advice regarding this particular problem, and maybe pointers to a way around it. All the best. John.

I doubt it would work very well at all connecting a 0.01uF capacitor between pin 3 of V2 and chassis....

Connecting a 0.01uF between pin 5 of V3 and chassis would immobilize the AGC.

The 100pF capacitor (C14 Trader sheet) will in effect, have 250 volts DC across it, needs to be rated at least that voltage 500 volt ones are available from the likes of RS, Farnell etc, there may be other suppliers.

Lawrence.

longneck90 · 11th Jan 2018, 10:01 pm

Hello to all. To Mike and Lawrence. Thanks for your help. Even though I have no way of testing the valves, the metallic screening is not damaged. I will look on that auction site for capacitors. I did look on the RS website, but was unable to locate suitable ones. Ie. 100 pf, high voltage. I will have another look. I had begun to think that such capacitors weren't made anymore. All the best. John.

Nuvistor · 11th Jan 2018, 10:17 pm

CPC

http://cpc.farnell.com/murata/de2b3k...0pf/dp/CA06005

longneck90 · 12th Jan 2018, 3:17 pm

Hello to all. To Frank. Sometimes, we cannot see the wood for the trees. I got capacitors today at Cricklewood Electronics, which is only walking distance away. I have installed one between Pin 3, V2, and Pin 5, V3, but the whistling/squealing is still present. I will investigate further. All the best. John.

11th Jan 2018, 6:02 pm	#1
longneck90 Hexode Join Date: Sep 2013 Location: Wembley, London, UK. Posts: 395	Ferguson 450, capacitor query. Hello to everyone, I recently rewound mains transformer for this radio, as original voltage seemed too low. When I asked it to produce music and the other stuff that radios receive, the result was violent whistling, and as the radio was tuned nearer to the received station, the output was mostly unintelligable. Ie. badly distorted. Eventually, I discovered, that, by attaching an 0.01 uf capacitor, between Pin 5, V3, and earth, reception improved dramatically, though a tiny bit 'wolly'. When I re-aligned the Intermediate Frequencies (IFs) Reception was perfect. What I only now notice, is that, I had replaced C14, which is between the Anode of Valve 2, and Pin 5 of Valve 3... and, that this capacitor is supposed to be 100 pf. The voltage at the Anode of V2 is 250 Volts, yet, I cannot find a 100 uf capacitor with a rating of more than 100 volts. Therefore, I was wondering why the radio works well when I have a 0.01 uf capacitor connected between Pin 3, V2 and earth, and is there some mistake about a capacitor of 100 pf, rating of 100 volts, situated between Pin 3, 250 Volts, and Pin 5 V3. Even though the radio is working well now, it is obviously not the way it was intended to work. (according to circuit diagram) I would be grateful for any information or advice regarding this particular problem, and maybe pointers to a way around it. All the best. John. Attached Thumbnails

11th Jan 2018, 6:15 pm	#2
crackle Rest in Peace Join Date: Mar 2011 Location: Basildon, Essex, UK. Posts: 4,100	Re: Ferguson 450, capacitor query. Ebay have 100pf high voltage capacitors. Search for; 10pF- 10nF 1/2/3 KV High Voltage/HV Ceramic Disc Capacitors Could the violent whistling and distortion have been caused by instability as a result of bad screening of valves. Mike

11th Jan 2018, 10:01 pm	#4
longneck90 Hexode Join Date: Sep 2013 Location: Wembley, London, UK. Posts: 395	Re: Ferguson 450, capacitor query. Hello to all. To Mike and Lawrence. Thanks for your help. Even though I have no way of testing the valves, the metallic screening is not damaged. I will look on that auction site for capacitors. I did look on the RS website, but was unable to locate suitable ones. Ie. 100 pf, high voltage. I will have another look. I had begun to think that such capacitors weren't made anymore. All the best. John.

11th Jan 2018, 10:17 pm	#5
Nuvistor Dekatron Join Date: Aug 2013 Location: Wigan, Greater Manchester, UK. Posts: 9,433	Re: Ferguson 450, capacitor query. CPC http://cpc.farnell.com/murata/de2b3k...0pf/dp/CA06005 __________________ Frank

12th Jan 2018, 3:17 pm	#6
longneck90 Hexode Join Date: Sep 2013 Location: Wembley, London, UK. Posts: 395	Re: Ferguson 450, capacitor query. Hello to all. To Frank. Sometimes, we cannot see the wood for the trees. I got capacitors today at Cricklewood Electronics, which is only walking distance away. I have installed one between Pin 3, V2, and Pin 5, V3, but the whistling/squealing is still present. I will investigate further. All the best. John.