29-04-2011, 10:35 AM
As I'd hoped, my newly acquired Ekco has an EL84 as an output valve so I tried that in this set last night and the hum was just the same.
I then attempted Alan's "Logical Approach" and took each of the valves out in turn. Removing the ECH81 and EF89 made little, if any, difference, but without the EBC81 the hum went. Connecting an audio source to pin 2 of the EL84 with the set in this state produced a clean output.
I got my megger onto this with the following results
Pin 1 to 2 = 100MΩ or 40MΩ depending which way I connected the leads
Pin 1 to 3 = 40MΩ/5MΩ
Pin 2 to 3 = 150MΩ/10MΩ
For all I know these are indicative of normal operation and I also realise that they don't properly add up but the meter scale isn't calibrated for great accuracy.
I'm also a but suspicious as that is the only Brimar valve in the set, all the rest are Mullards, so I wonder if it's given trouble before. I've already discovered that R8 (RTS data) is high but don't have a replacement to hand. At least I'll soon be getting new caps for my Ekco so will be able to get one then.
Cheers
- Joe
I then attempted Alan's "Logical Approach" and took each of the valves out in turn. Removing the ECH81 and EF89 made little, if any, difference, but without the EBC81 the hum went. Connecting an audio source to pin 2 of the EL84 with the set in this state produced a clean output.
I got my megger onto this with the following results
Pin 1 to 2 = 100MΩ or 40MΩ depending which way I connected the leads
Pin 1 to 3 = 40MΩ/5MΩ
Pin 2 to 3 = 150MΩ/10MΩ
For all I know these are indicative of normal operation and I also realise that they don't properly add up but the meter scale isn't calibrated for great accuracy.
I'm also a but suspicious as that is the only Brimar valve in the set, all the rest are Mullards, so I wonder if it's given trouble before. I've already discovered that R8 (RTS data) is high but don't have a replacement to hand. At least I'll soon be getting new caps for my Ekco so will be able to get one then.
Cheers
- Joe
