Linear L50 Mains transformer Fault - Page 2 - UK Vintage Radio Repair and Restoration Discussion Forum

bobbyd123 · 1st Jul 2020, 8:50 pm

Hi Techman Thanks
Capacitors on order Resistors out of spec I have.
I will be taking out the smoothing caps and checking them on my EICO 950 Tester
On my radios most times I re-stuff them
Cheers

bobbyd123 · 1st Jul 2020, 9:20 pm

I just been thinking
Will 450volt rated smoothing caps be okay there is one single can 32uf capacitor found to be rated at 500volts I have decided to replace them
Thanks

Techman · 2nd Jul 2020, 12:45 am

The original ones could be OK.

Don't jump to conclusions regarding their state until you've gone through the reforming process with them - this will very soon show whether it's one of them that has caused the problem with the transformer.

The best thing to do is to replace the two coupling capacitors to the output valves and use the lamp limiter in series with the mains input to test the state of play when you re-fit the mains transformer. With a 'lamp' in series with the mains supply, very little damage can be done if anything goes wrong and you can assess the unit for potential faults and take readings - particularly the HT voltage, remembering that it will be a bit on the low side due to the series 'lamp', but it gives you a rough idea of any problems. Assuming that it has a valve rectifier, it would be a good idea to power up first with the limiter with this valve removed, obviously there will be no HT at this stage, but it tests the heater circuit etc.

If the amplifier originally had 500 volt rated smoothing, then that's what it needs - and NO less, so test and reform the originals if possible.

vidjoman · 2nd Jul 2020, 9:01 am

I think the working DC voltage in this amp is around 490v. Before the output valves warm up the voltage could be closer to 600v. Normally caps are rated as xxx working voltage, in this case 500v, and it's max voltage will be zzz although not often quoted these days. I often get concerned when caps used further down the line from the rectifier are lower voltage rated as they too can be subject to higher than working voltage when the output valves are cold. Rectifier valves usually heat up quicker than the outputs.

bobbyd123 · 2nd Jul 2020, 9:24 pm

Is it possible to use my EICO 950 To reform the smoothing capacitors
Just a thought

1st Jul 2020, 8:50 pm	#21
bobbyd123 Triode Join Date: Jun 2019 Location: Birmingham, West Midlands, UK. Posts: 48	Re: Linear L50 Mains transformer Fault Hi Techman Thanks Capacitors on order Resistors out of spec I have. I will be taking out the smoothing caps and checking them on my EICO 950 Tester On my radios most times I re-stuff them Cheers

1st Jul 2020, 9:20 pm	#22
bobbyd123 Triode Join Date: Jun 2019 Location: Birmingham, West Midlands, UK. Posts: 48	Re: Linear L50 Mains transformer Fault I just been thinking Will 450volt rated smoothing caps be okay there is one single can 32uf capacitor found to be rated at 500volts I have decided to replace them Thanks

2nd Jul 2020, 12:45 am	#23
Techman Dekatron Join Date: Nov 2009 Location: Lincolnshire, UK. Posts: 5,000	Re: Linear L50 Mains transformer Fault The original ones could be OK. Don't jump to conclusions regarding their state until you've gone through the reforming process with them - this will very soon show whether it's one of them that has caused the problem with the transformer. The best thing to do is to replace the two coupling capacitors to the output valves and use the lamp limiter in series with the mains input to test the state of play when you re-fit the mains transformer. With a 'lamp' in series with the mains supply, very little damage can be done if anything goes wrong and you can assess the unit for potential faults and take readings - particularly the HT voltage, remembering that it will be a bit on the low side due to the series 'lamp', but it gives you a rough idea of any problems. Assuming that it has a valve rectifier, it would be a good idea to power up first with the limiter with this valve removed, obviously there will be no HT at this stage, but it tests the heater circuit etc. If the amplifier originally had 500 volt rated smoothing, then that's what it needs - and NO less, so test and reform the originals if possible.

2nd Jul 2020, 9:01 am	#24
vidjoman Dekatron Join Date: Jun 2013 Location: East Sussex, UK. Posts: 3,326	Re: Linear L50 Mains transformer Fault I think the working DC voltage in this amp is around 490v. Before the output valves warm up the voltage could be closer to 600v. Normally caps are rated as xxx working voltage, in this case 500v, and it's max voltage will be zzz although not often quoted these days. I often get concerned when caps used further down the line from the rectifier are lower voltage rated as they too can be subject to higher than working voltage when the output valves are cold. Rectifier valves usually heat up quicker than the outputs.

2nd Jul 2020, 9:24 pm	#25
bobbyd123 Triode Join Date: Jun 2019 Location: Birmingham, West Midlands, UK. Posts: 48	Re: Linear L50 Mains transformer Fault Is it possible to use my EICO 950 To reform the smoothing capacitors Just a thought