Why did my TX Burn out Help

[colin.hepburn]

Ok I am sure He won't mind me posting his email rely to me about this Transformer spec
First if I want to buy a TX of say 200VA@200mA I am looking for the 200mA after Rectification as for example as Hammond Spec there TXs in DC not AC so even the label on my Hammond 260G says 173VA@200mA DC The ask jan was 200VA@200mA which I took to be 200mA DC but it not


Any way here's a cut and paste of part of the email from Dave Brooks of Danbury Transformers here's his Take on this
Well,we're all confused now.
Could do with the full spec from the German firm.
They are right in that most European tx mfrs.quote AC or RMS values,in other words assuming straightforward ac resistive load (they have translated as 'ohmic').
The power supply designer should then convert this to suitable DC figure for particular rectifier circuit.
When you add all the 270 and 50v wdgs in series you will have a secondary of 320- 0 -320vAC,rated at 200mA AC if it were connected to a 3.2K res.load.(128VA)
If connected to a full wave bi-phase rectifier( two diodes,alternating each half-cycle),dc after rect would be about 120mA.However the TX could really take 250mA ac,as there is a cooling effect as each half of HT winding is only conducting alternate cycles.Then the dc could be around 150mA.

[Nick]

But I don't see how any TX makers can provide a DC rating for their windings, its out of their hands what the user does with them. Choke input, cap input, voltage doubler, voltage tripler, bridge, half wave, full wave. All will produce a different DC current from the same windings.

[colin.hepburn]

That's not the point
Hammond do say Secondary: High voltage designed for full wave C.T. use in there adds so that tells me if its rated for 200mA and used full wave CT then its spec is for the 200mA DC no-one is suggesting using it any other way the Hammond chart gives you that and as i said its backed up on the label on the TX

[Nick]

Fine, use Hammond TX's then, but you won't find many other TX winders that do the same (or should you expect them to).

[Paul Barker]

Collin, what Hammond say, if you are interpreting it correctly, simply results in a transformer with unpredictable final voltages. This is because of what is known as"regulation". As Nick said, the rating depends on use; therefore the secondary voltage depends on use because of regulation.