Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: frank57 on June 23, 2012, 03:43:54 pm
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On a Power transformer with a center tap for the heaters should the voltage be dead zero on it,if I take a measurement?
Without tubes in the amp or with tubes in there?
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Between the CT and ground you can't measure a voltage if one of the other legs of the windings isn't connected in some way to ground
EDIT: I'm assuming you didn't connected the CT to ground of course
K
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On a Power transformer with a center tap for the heaters should the voltage be dead zero on it,if I take a measurement?
Without tubes in the amp or with tubes in there?
I'd say yes in either case unless you have connected it either to the cathode of a power valve (> 10VDC or more) or to a potential divider from the HT (more than 70VDC for instance)...unless I'm terribly wrong. :icon_biggrin:
Yet some experts here could certainly be more helpful than I am...
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The heaters center tap can be connected to a DC supply , usually around 50V , to assure a quiet operation. That is called 'elevated heaters' and can be taken out from a power tube cathode or from the B + supply, through a voltage divider, usually 220K and 10k or up to desired voltage. You can search for a schematic here or somewhere else for further explanations ( maximum cathode to heater voltage etc ).
Colas
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The real question, is can you get any power at the voltage you are reading.
No it's not. The real question is where is the black lead of your meter connected and where is the red lead of your meter connected? And what mode is the meter in?
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What sluckey said. Voltage between the center tap and some other point may be inadvertent or inherent in the design. As far as the heaters, voltage between the tap (at "relative ground") and the winding ends are what you're interested in.
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Where you been so long?
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Oh man, life's been crazy. I actually took the day off to clean up my bench. I haven't melted solder on anything (on purpose) in almost two years. I've got a radio on the bench in the middle of a restore, which is exactly the way I left it in February 2011. Like I said, though, life's been crazy. I'll post something in a more appropriate spot here and try to do some catching up.
If I can ever catch up, that is...
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Back to the question:
On a Power transformer with a center tap for the heaters should the voltage be dead zero on it,if I take a measurement?
Where are you applying your meter leads (i.e., where is the black lead, where is the red lead)? Is your meter set to read a.c. or d.c. voltage? What exactly are you trying to measure? What does your meter indicate?
Without this information, the answer is, "Depends..."
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I don't understand what you're asking.
Is your CT grounded?
If your CT is grounded and you're measuring between CT and ground, then what are you measuring? Maybe you have a bad ground connection.
If you are asking should the CT always be connected to ground, then no, there are cases where the CT isn't grounded.
(ie: if the CT is connected to some point other than ground, you would get a voltage and that's OK)
Do you have a schematic?