Transformer Screen & Signal Grounding Issues

[AndrewT]

how do i measure the dc bias across the output cap?

set your DMM to 200Vdc.
Carefully attach the measuring probes to the two terminals of the capacitor.

C4 & C6 are simply part of a big RC filter between the rectifier and the amplifier.
This filter will not stop the output capacitor charging nor discharging.

 

[mymindinside]

You either accept that charging/discharging current passing through your speaker or you fit a speaker isolation switch or relay to provide an alternative current path. You must have a current path. There is no charging/discharging if you leave output open ended during the switching.

Would resistors R13, R15, and R15 (all 47R 3W) provide the current path for charging/discharging if there were no speakers connected? these resistors are connected across the output; i.e. from the negative leg of the output capacitor to ground.

cheers,
mymindinside

 

[AndrewT]

Would resistors R13, R15, and R15 (all 47R 3W) provide the current path for charging/discharging if there were no speakers connected?

I was not paying attention.
These three resistors effectively give 15r in parallel to the speaker load.
At 9W rating they are going to get more than a bit warm.