20-07-2015, 07:35 PM
I have made the adapter and the good news is that it worked first time.
The results where a big anticlimax. The hum was still there at 100mv across the voice coil at 100hz.
It is clearly not coming from the heater circuit as it is now identified as coming from the power supply.
The prime suspect now is the reservoir capacitor that is clearly visible behind the phase splitter valve.
The negative wire just goes to a solder tag under a screw right next to the capacitor and that is how it was wired as found.
The preamp valve has lost almost all of the screening but it only hums at 50hz if you touch the glass bulb so it is not the source of the hum even with that bad screening.
The results where a big anticlimax. The hum was still there at 100mv across the voice coil at 100hz.
It is clearly not coming from the heater circuit as it is now identified as coming from the power supply.
The prime suspect now is the reservoir capacitor that is clearly visible behind the phase splitter valve.
The negative wire just goes to a solder tag under a screw right next to the capacitor and that is how it was wired as found.
The preamp valve has lost almost all of the screening but it only hums at 50hz if you touch the glass bulb so it is not the source of the hum even with that bad screening.