Bradford TV set. - Page 2 - UK Vintage Radio Repair and Restoration Discussion Forum

Paul.Dorman · 29th Oct 2016, 8:35 pm

I have changed the valves and it's still the same I tried disconnecting the tripler and no real difference I have tested every cap in the tv and thay are fine but valves glow white when switch on I think that there is a fault on the power supply and there is only about 300 volts on the boost valve top connection. I will check for negative volts and get back to you.

Thanks for your help

Welsh Anorak · 31st Oct 2016, 4:25 pm

Hi
I wouldn't expect there to be a power supply fault - there's not much to it and the fact you've 300v knocking around the LOP stage implies it's doing its job. The bright valve problem is nothing to worry about especially as you've replaced the valves. They always used to do that - customers would know something was amiss when they didn't get that brief glow reflected on the wall behind.
The key measurements are on the PL509's base. Expect around 250-300v at pin 6 and about -40v at pin 1 and 8 once the oscillator's come into play. If your voltage is missing at pin 6 then the 2.7k 5W screen grid feed resistor is open circuit. This would cause an unstressed line stage.
There's a 'sticky' at the top of this section detailing the operation of a valve line stage which is handy if you need to brush up on its operation.

philips KT3 · 31st Oct 2016, 7:04 pm

I started my TV rental business with the Bradfords but quickly moved on to the Decca 80 sets then my favourite sets ever the Philips KT3. Have you ever lifted a Decca Bradford? How can you gents remember the faults from so long ago/ I meant to say a 22 inch, or may have even been a 26 inch Bradford.

Gerard

29th Oct 2016, 8:35 pm	#21
Paul.Dorman Retired Dormant Member Join Date: Oct 2016 Location: Essex, UK. Posts: 6	Re: Bradford TV set. I have changed the valves and it's still the same I tried disconnecting the tripler and no real difference I have tested every cap in the tv and thay are fine but valves glow white when switch on I think that there is a fault on the power supply and there is only about 300 volts on the boost valve top connection. I will check for negative volts and get back to you. Thanks for your help

31st Oct 2016, 4:25 pm	#22
Welsh Anorak Dekatron Join Date: Apr 2005 Location: North Wales, UK. Posts: 6,916	Re: Bradford TV set. Hi I wouldn't expect there to be a power supply fault - there's not much to it and the fact you've 300v knocking around the LOP stage implies it's doing its job. The bright valve problem is nothing to worry about especially as you've replaced the valves. They always used to do that - customers would know something was amiss when they didn't get that brief glow reflected on the wall behind. The key measurements are on the PL509's base. Expect around 250-300v at pin 6 and about -40v at pin 1 and 8 once the oscillator's come into play. If your voltage is missing at pin 6 then the 2.7k 5W screen grid feed resistor is open circuit. This would cause an unstressed line stage. There's a 'sticky' at the top of this section detailing the operation of a valve line stage which is handy if you need to brush up on its operation.

31st Oct 2016, 7:04 pm	#23
philips KT3 Triode Join Date: Sep 2016 Location: Chester, Cheshire, UK. Posts: 37	Re: Bradford TV set. I started my TV rental business with the Bradfords but quickly moved on to the Decca 80 sets then my favourite sets ever the Philips KT3. Have you ever lifted a Decca Bradford? How can you gents remember the faults from so long ago/ I meant to say a 22 inch, or may have even been a 26 inch Bradford. Gerard