First... thanks for all the help so far on my other postings.

I'm working on an Ingrahm chassis that has a hum independent of volume control setting. I haven't taken a scope to it yet to see if it is induced in the AF stage (power supply, open resistor, etc.). I was curious first as to the failure modes of the speaker field coil itself. I have re-capped the power supply and checked the rectifier tube (tested and even replaced). The hum was unaffected. Does anyone have words of wisdom prior to me checking everything out?

Thanks

Hi Scott

I would double check the electrolytic filter cap connections. In most cases they are responsible for loud hum. Were replacement values at least as high as originals? If the hum is minor check shielding and tubes for leakage.

The field will be ok unless it is open.

Norm

: First... thanks for all the help so far on my other postings.

: I'm working on an Ingrahm chassis that has a hum independent of volume control setting. I haven't taken a scope to it yet to see if it is induced in the AF stage (power supply, open resistor, etc.). I was curious first as to the failure modes of the speaker field coil itself. I have re-capped the power supply and checked the rectifier tube (tested and even replaced). The hum was unaffected. Does anyone have words of wisdom prior to me checking everything out?

: Thanks

Hi,
If the chcecks that Norm suggest turn up nothing, check your tubes for filament to cathode short. You might want to check to see if there are caps going from the power cord (line) to the chassis, these can sometimes fail and lead to a hum. Sometimes you can also have a hum due to a previous repair not having been done correctly, or wires simply not dressed back in a manner prevent inductive pickup.

One other possible thing to try, which works of the transformerless types of chassis, is to flip the plug in the wall socket.

: Hi Scott

: I would double check the electrolytic filter cap connections. In most cases they are responsible for loud hum. Were replacement values at least as high as originals? If the hum is minor check shielding and tubes for leakage.

: The field will be ok unless it is open.

: Norm

:
: : First... thanks for all the help so far on my other postings.

: : I'm working on an Ingrahm chassis that has a hum independent of volume control setting. I haven't taken a scope to it yet to see if it is induced in the AF stage (power supply, open resistor, etc.). I was curious first as to the failure modes of the speaker field coil itself. I have re-capped the power supply and checked the rectifier tube (tested and even replaced). The hum was unaffected. Does anyone have words of wisdom prior to me checking everything out?

: : Thanks