Arfa Daily wrote:


The VA rating and regulation percentage of commercial mains transformers
closely follows their primary resistance, not by any simple formula but
ones with the same resistance have similar VA ratings.

Egs, for 240V rated transformers:

50VA = 60 ohms & 13%
160VA = 12 ohm & 8%
300VA = 4.7 ohms & 4%
800VA = 1.4 ohms & 4%
1000VA = 1.1 ohms & 4%



That's an interesting observation, Phil. I will keep that noted, as it's
potentially a good 'reverse lookup' for determining if a tranny has shorted
turns on its primary, if you know its VA rating


** That is a big "if" - cos with transformers fitted to commercial products it is not published.

I keep an index book with primary ohm values for commonly seen gear, also the mains rms current draw at idle, with standby off and on - if it exists.

Egs:

Marshall JTM60; 6.5ohms (250VA) 0.16A, 0.44A

Marshall VS100; 10.2ohms (175VA) .17A

Phase Linear 400; 1.9ohms (600VA) .17A

Roland Cube 60; 12ohms (160VA) .1A



..... Phil