Pilot Little Maestro Pilot Lamp Conversion - Page 3 - UK Vintage Radio Repair and Restoration Discussion Forum

julie_m · 9th Oct 2018, 10:56 pm

The problem with using X capacitors as voltage droppers is the self-healing and consequent loss of capacitance. Every switch-on surge (a cold valve heater, or a discharged capacitor, is almost a dead short circuit) tends to weaken the capacitor a bit until eventually there is insufficient power available and the circuit begins to misbehave, requiring replacement of the capacitor.

The company I used to work for did some tests and found it was better just to use a standard 400 or 630V capacitor, with a fusible resistor to limit the switch-on surge.

Sideband · 10th Oct 2018, 10:43 pm

What's happened to Kings? We still don't know for sure what the correct valve line-up is.

usradcoll1 · 11th Oct 2018, 3:25 am

Quote:

Originally Posted by Sideband

What's happened to Kings? We still don't know for sure what the correct valve line-up is.

The correct valve line-up was specified in entry #16.
I'm surprised that the # 21 post was so incorrect! I'm rather familiar with this valve line-up.
It seems that Brimar was the main supplier of the US type valves used in the British built radios.
This really was an informative and interesting thread!

9th Oct 2018, 10:56 pm	#41
julie_m Dekatron Join Date: May 2008 Location: Derby, UK. Posts: 7,735	Re: Pilot Little Maestro Pilot Lamp Conversion The problem with using X capacitors as voltage droppers is the self-healing and consequent loss of capacitance. Every switch-on surge (a cold valve heater, or a discharged capacitor, is almost a dead short circuit) tends to weaken the capacitor a bit until eventually there is insufficient power available and the circuit begins to misbehave, requiring replacement of the capacitor. The company I used to work for did some tests and found it was better just to use a standard 400 or 630V capacitor, with a fusible resistor to limit the switch-on surge. __________________ If I have seen further than others, it is because I was standing on a pile of failed experiments.

10th Oct 2018, 10:43 pm	#42
Sideband Dekatron Join Date: Oct 2003 Location: Croydon, Surrey, UK. Posts: 7,567	Re: Pilot Little Maestro Pilot Lamp Conversion What's happened to Kings? We still don't know for sure what the correct valve line-up is. __________________ There are lots of brilliant keyboard players and then there is Rick Wakeman.....