10-30-2017, 04:36 PM
Sam
To elaborate on what Ron said, some tubes, especially directly heated like the 6B4G (my version BTW has 6A5, indirectly heated - 37-116 came in both ways) will produce some hum due to the filaments being fed 60Hz (oops...sorry...cycles) AC.
Introducing a low Ohms trimpot with he wiper to the GND allows to minimize the hum.
It is likely that the trimpot was not touched so it might still be in the position to null out the hum.
To elaborate on what Ron said, some tubes, especially directly heated like the 6B4G (my version BTW has 6A5, indirectly heated - 37-116 came in both ways) will produce some hum due to the filaments being fed 60Hz (oops...sorry...cycles) AC.
Introducing a low Ohms trimpot with he wiper to the GND allows to minimize the hum.
It is likely that the trimpot was not touched so it might still be in the position to null out the hum.
People who do not drink, do not smoke, do not eat red meat will one day feel really stupid lying there and dying from nothing.
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