At low levels its should not cause too much trouble and if you work out
the dc magnetisation
in Tesla for an average OPT then as long as the dc field isn't more than
1T then
there is still some ability for ac magnetisation. The lower the effective
µ, the greater the
tolerance for dc imbalalance which is the equivalent of the net imbalance
applied from a to a so
maybe 10mA dc a-a in the case above.
I don't exactly know what 10mA dc will do with a toroidal OPT with max µ =
40,000,
amd say Afe = 50 mm x 30mm, ML = 350mm, and Np = 2,000 turns.

But a core of E&I won't magnetize so easily; placing a fine air gap in a
pair of C cores or E&I lams
in a PP tranny can still give plenty of primary inductance, but very much
improve the tolerance
for dc offset currents.


Some years ago, I used a power transformer for an output transformer in
an AM table radio. Without gapping it. Though the 60 or so ma of DC
from the single ended pentode feeding it didn't seem to bother it any.
The transformer was intended to produce 12V centertapped at around 3
amps. The speaker loads half the secondary.

I'd like to get a better understanding of what the DC and the audio is
doing to this transformer and why it seemed to work when it "shouldn't"...