Ground/Float Center Tap on Power Transformer?

[Ethan]

Is it usually the case that the center tap of the pri or sec is referenced to ground if it is not being used?

Thanks!

 

[dale116dot7]

Not normally. It is normally referenced to ground in full-wave split-supply configurations (eg. powering op-amps with +/- 15 volt rails) but if its supplying something like a Neve with a single 24 volt supply, then the centre tap should not be connected.

 

[NewYorkDave]

And definitely don't ground any taps on the primary!

 

[Ethan]

A 6.3V Heater center tap should always be grounded, correct?

Thanks fellers!

 

[NewYorkDave]

Not always. Are you running the heaters on AC or DC?

It's often grounded in an AC heater supply; but then again, in some cases balancing the supply (with respect to ground) with resistors or a pot works better. In any case, the heater supply must be referenced to circuit ground and cannot be allowed to just float.

 

[Ethan]

Thanks Dave.
AC heaters. Until now I haven't had a TX with a center cap on the heater winding.

But with a DC supply wouldn't you float the center tap (if there was one) and ground the negative side? Or is that too general to be a rule of thumb.

 

[NewYorkDave]

You're right.

 

[Rob Flinn]

On a side note, if you end up with spare secondaries on a mains tx, do you "terminate" them in some way or just leave them floating around (with leads secured of course) ?

My mind says just leave'em..

I`d thought about this in the past, because it definately isn`t good to use a valve power amp without a speaker or load connected. For example using the DI out of an AMPEG head..

However it MAY be that if at least one secondary in a transformer is loaded then this isn`t a problem.

I rebuilt & uprated the op amp supply in my desk PSU. This involved putting new transformers in. This means that the tap on the original transformer is no longer used. Should this be terminated in some way with maybe an led or something ?
Can someone enlighten me?

 

[NewYorkDave]

We were talking about power transformers.

 

[CJ]

Yes normally the center tap of a fil x-former gets grounded for least hum.
If making dc from 6.3, you put both outside wires into a bridge rectifier.

 

[clintrubber]

from Ethan:

Is it usually the case that the center tap of the pri or sec is referenced to ground if it is not being used?

To my surprise the center tap of the Trident CB9146 pow-TX wasn't connected to gnd either (see btm of schematic).
I don't see any reason for NOT grounding it.

Bye,

Peter