Please tell me if what I am finding is normal. In trying to discover a common connection that would effect both channels a with the hum buzz I described in previous posts.
With the all the tubes disconnected and power cord off I measured the power transformer connections to the board, T1-1 through T1-8 in reference to ground. Not Neutral but Ground. Before I give the numbers I would like to mention that the ground on the board and the ground of the RCA jack and the shield for the input coax are all attached to a single ground lug on the top plate of the amp. So I am using the top plate to connect one lead of my DVM.
All the below measurements are taken from their taps to ground
the 5 Volt taps T1-2 and T1-3 and both in the mohm range - seem good
The center tap for the H.V. (T1-1)is 0 ohm or continuity (normal as per Schematic)
The H.V. taps T1-4 and T1-5 are at 178 ohm (I assume this is the resistance of the transformer plus the 100 ohm resistor I use to keep the output below 300 volts but is this indicate a problem)
The center tap T1-6 and both 6.3 volt taps T1-7 and T1-8 all measure 0 ohms resistance to ground. The center tap hear is per schematic but why would the 6.3 volt taps be grounded? Does this reflect the ground for the Sharp regulator ?
With the all the tubes disconnected and power cord off I measured the power transformer connections to the board, T1-1 through T1-8 in reference to ground. Not Neutral but Ground. Before I give the numbers I would like to mention that the ground on the board and the ground of the RCA jack and the shield for the input coax are all attached to a single ground lug on the top plate of the amp. So I am using the top plate to connect one lead of my DVM.
All the below measurements are taken from their taps to ground
the 5 Volt taps T1-2 and T1-3 and both in the mohm range - seem good
The center tap for the H.V. (T1-1)is 0 ohm or continuity (normal as per Schematic)
The H.V. taps T1-4 and T1-5 are at 178 ohm (I assume this is the resistance of the transformer plus the 100 ohm resistor I use to keep the output below 300 volts but is this indicate a problem)
The center tap T1-6 and both 6.3 volt taps T1-7 and T1-8 all measure 0 ohms resistance to ground. The center tap hear is per schematic but why would the 6.3 volt taps be grounded? Does this reflect the ground for the Sharp regulator ?
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Mkane I would like ti say that last night I added a 2.2uF poly cap from ground to the plate side of the output transformers. Measured noise at the speaker outputs went from 24 mv to 8mv. I will move the caps to the 10 ohm resistor side and see if that makes any difference. Then I will try swapping orientation of the HV leads to the board and then the 6.3 volt leads to see if that makes any change.
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