Heater circuit ground reference

ducati guy · 5172

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Offline ducati guy

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on: November 23, 2009, 02:02:56 AM
I recently picked up a pair of Magnequest PGP 8.1 power transformers to use in a 45 based amp. Wasn't aware that the 6.3 V supply for the driver tube is not center tapped. Do I need to reference the voltage to ground through a pair of resistors or can it float?

Conrad



Offline Grainger49

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Reply #1 on: November 23, 2009, 02:30:00 AM
I can't really answer about a power amp, but I built a preamp quite a few years back and it hummed like a mother till I grounded one leg of the heater supply.  



Offline Len

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Reply #2 on: November 23, 2009, 03:53:52 AM
I recently picked up a pair of Magnequest PGP 8.1 power transformers to use in a 45 based amp. Wasn't aware that the 6.3 V supply for the driver tube is not center tapped. Do I need to reference the voltage to ground through a pair of resistors or can it float?

Conrad

I think it's internally grounded. I didn't ground the heater supply in my Paraglows, IIRC, and they sound fine.

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Offline Grainger49

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Reply #3 on: November 23, 2009, 04:55:41 AM
OUCH!  If they are internally grounded don't ground the transformer or the DC output.  Check for a ground to the frame of your transformer from each lead of your transformer.  If it reads open then it is safe to ground one leg of the DC supply.  I use the negative, I don't know if it makes a difference.



Offline Doc B.

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Reply #4 on: November 23, 2009, 05:19:17 AM
The 6.3V winding is not grounded to anything inside a PGP 8.1 transformer. It's hard to give a definitive answer without knowing the actual circuit, but assuming that the driver tube does not have its cathode sitting at a high potential relative to ground (i.e., its grid is not direct coupled to a high voltage input stage that sits before it in the circuit) you would most likely want to ground the 6.3V secondary.

Dan "Doc B." Schmalle
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Bottlehead Corp.


Offline Len

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Reply #5 on: November 23, 2009, 05:26:10 AM
Darn! Glad you guys stepped in. My memory seems to be going.

And my memory seems to be going, too.

Paramours
Paraglows
Excites
Heavily modded Soul Sister and Groove Thang
Quickie modded to active low pass filter
Quickie modded to headphone amp
Lots of Bottlehead parts used for building other stuff