Question on power transformer output specification convention

[Porksoda]

When a power transformer is said to have an output of 100-0-100, does this mean that it will output +/-100V RMS w/ the center tap connected to ground, so that if you were to use a choke after it you would get approximately 200V total?

 

[rickcr42]

it means you will have two 100v outputs for making a +/- 100 volt power supply if using the center tap or a single 200 volt output if the tap is unsused.

the center tap is just that-a "tap" at the center of the secondary winding

 

[rickcr42]

BTW-if this were an audio transformer the taps would be equal divisions of the main output impedance instead of output voltage :

so a 16 ohm output transformer can have taps at 8 ohms (1/2) and 4 ohms (1/4 rare)

and a 600 ohm output line transformer can have the intitial 600 ohms (line out ),300 ohms (line out at 1/2) and possible 150 ohms (line or headphone output at 1/4)

 

[Porksoda]

So one more question: For a CT power transformer. Suppose it is a 200-0-200 rated at 100mA. If I paralell the two halves can I get 200Vrms at 200mA? Is paralleling necessary at all in this situation?

 

[rickcr42]

you may find this diagram helpful

http://www.hammondmfg.com/5CHook.htm

some but not all transformers allow for either series or parallel connection of the outpuyts

series=the normal V/A rating of the transformer ,with C.T.
parallel=1/2 the voltage but double the current,no C.T.

You lose the center tap in this doubled current configuration so for a dual polarity power supply+/-15 VDC for example,you would need two transformers instead of one for a full power supply.

Not that this is a bad thing.

 

[Porksoda]

Yeah, that's pretty much what I thought with regard to wiring. I was thinking about the whole center tap thing. At first I thought I could just take a 275-0-275 hammond transformer and put it in parallel for a morgan jones power supply, but then it occurred to me there is nowhere for the return ground current to go. I mean I could use a virtual ground circuit, but that would be cheating.

Where can one get a decent 100-0-100 power transformer, anyway? I looked in the links section but couldn't find any surplus dealers.

 

[rickcr42]

Quote:

Where can one get a decent 100-0-100 power transformer, anyway? I looked in the links section but couldn't find any surplus dealers.

You know what ? you are right man !

I have not been in the links section for a while and I thought I had a surplus electronics dealers section and i don't

I will amend that today.Really an essential parts source for "one of" projects that require expensive parts like transformers and large heat sinks.

first of all you mention you need 100-0-100 for your planned Morgan Jones amp.are you forgetting the heater supply for the tubes

An all-in-one power transformer is best if you want to keep the cost down,the size of the amp tidy and ease the layout requirements.

It can be hard enough getting the layout right in a tube amp with just a single unit but two would be a lot harder if you are doing a one box amp.If two boxes (amp/ps) you can have as many as you need including two 100 volt trasformers with the primaries in parallel and one secondary lead attached to the other as a center tap.this is the electrical equivelant of a single center tapped transformer but again gets into layout and size issues.

brand new I would look at the offerings at www.tubesandmore.com

They carry the Hammonds,the One Electron transformers and every once in a while small lots of "no names" which are just as good.

For surplus "used" and pulled from equipment check with Surplus Sales Of Nebraska.They recently upgraded the web site and it looks like maybe the prices also went up but still a nice resource for the hard to find or unusual

http://www.surplussales.com/

This joint has a pretty extensive mixed new/nos listing of parts

http://www.surplussales.com/

I found these guys invaluable once when i need to fix a Sony Playstation.The whole drive was cheaper than any repair shop or console replacent.

http://www.mpja.com/

Nice source for high voltage electrolytic caps,dual audio pots,AC adapters and other parts-

http://www.goldmine-elec-.com/products.asp?dept=1222

This place is pretty unique.A bit hard to navigate and you never know what you will find but a great source for the obscure,the unique and for the one of a kind part

http://www.sciplus.com/

there are more but this should keep you busy for a bit

 

[Porksoda]

Thanks for the linkage! The first one, tubesandmore, seems to have a good selection of the hammonds at a really good price, including the 100-0-100 I need