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Tubelab Discussion and support of Tubelab products, prototypes and experiments

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Old 16th March 2017, 04:25 AM   #1
waltroman is offline waltroman  United States
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Default Help with TSE Grounding

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 ?

Last edited by waltroman; 16th March 2017 at 02:50 PM.
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Old 16th March 2017, 02:10 PM   #2
waltroman is offline waltroman  United States
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I edited the above post I made at 1:00 in the morning.
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Old 16th March 2017, 04:25 PM   #3
mkane77g is offline mkane77g  United States
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Help with TSE Grounding
Can't answer your question but, my measurements are similar to yours on all but 4 & 5 but I'm using a choke.
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Old 16th March 2017, 04:35 PM   #4
mkane77g is offline mkane77g  United States
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Help with TSE Grounding
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Old 16th March 2017, 10:03 PM   #5
waltroman is offline waltroman  United States
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Quote:
Originally Posted by mkane77g View Post
Can't answer your question but, my measurements are similar to yours on all but 4 & 5 but I'm using a choke.
Choke here also. What numbers did you get on 4 & 5
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Old 17th March 2017, 02:20 AM   #6
mkane77g is offline mkane77g  United States
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Help with TSE Grounding
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Old 17th March 2017, 02:40 AM   #7
waltroman is offline waltroman  United States
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Thanks for the help. You have gone above and beyond.
The more I looked at the schematic and thought about what I was seeing the numbers make sense. I think electrical engineers live on another plane of existence.
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Old 17th March 2017, 02:38 PM   #8
waltroman is offline waltroman  United States
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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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Old 28th March 2017, 12:12 AM   #9
waltroman is offline waltroman  United States
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Problem found. I had a cold solder joint on C1. Amp brought over to a friends house and he found the problem with the scope. That regulator played hell without the cap in the circuit. Dead quiet now!
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