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Se output transformer question

Hi all the question I have is, on a regular output transformer the large size of the core is needed do to the dc current going through it. Is this correct? So in a se para feed the output transformer only need to be big enough for the ac power going through it.

So I guess what I'm asking is a para feed output transformer can be much smaller then a normally set up se output tranny?

Sorry if it's worded a little cryptically.

Thanks a mill.

Nick
 

MQracing

diyAudio Member
2005-10-08 4:11 pm
www.magnequest.com
Hi Nick:

Yes.. parafeed outputs can be smaller than a series fed conventional single ended output trans that must carry the unbal dc plate current.

The unbal dc plate current--- "consumes" core capacity (flux)--- think of a core as a sponge--- it will have a finite capacity to absorb electrical energy--- i.e., a given core will have a max flux capacity. This flux capacity must be (in the case of the conventional SE) be able to accomadate both the DC flux as well as the AC flux. In a parafeed application there is no dc plate current in the primary and hence the core does not have to have the extra size necessary to handle the dc flux.

the parafeed output will (just as a general rule of thumb) only have to be the size of a similar power rated push-pull output transformer. As a rough rule of thumb a conventional SE output trans must be on the order of say up to 4 times the size of a normal push pull trans of the same power rating.

But keep in mind that if we count "total" iron--- that the parafeed arrangement still may be a large "consumer" of iron--- though the output trans can be built much smaller (sans the dc current duties)--- the plate choke (if you use a plate choke) will be moreso similar in size to a series fed conventional airgapped output--- the plate choke has to handle the dc plate current and the ac signal voltages.

Of course--- if you use a CCS as a plate load or a plate resistor then you would not need a plate choke. But if you do use a plate choke it tends toward being a larger unit physically.

MSL
 
I was wondering because I have 2 amorphous core pp trans that I am going to use in se parafeed. I figuered it had been done before just wanted to know.

How do you decide on the size of a parafeed choke to use? Im assuming it's juts reactance alone and nothing else warrants the size.

Nick