Bottlehead Forum
General Category => Technical topics => Topic started by: ducati guy on November 23, 2009, 02:02:56 AM
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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
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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.
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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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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.
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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.
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Darn! Glad you guys stepped in. My memory seems to be going.
And my memory seems to be going, too.