On Thursday, January 17, 2019 at 4:19:56 PM UTC-5, Phil Allison wrote:
wrote:




Core saturation is not a function of load "TO A FIRST ORDER APPROXIMATION".

Only the primary voltage matters.


** And of course the input frequency - the two operate in reverse proportion.


But to a second order, if the transformer core is near saturation
unloaded, when you load the secondary, the primary current and the
primary resistance will in effect LOWER the primary voltage and
reduce the core saturation.


** True even when the applied primary voltage has no changed one tiny bit cos it is coming form the mains supply.


So considering the second order effect of primary winding resistance,
yeah, loading a transformer _may_ reduce the distortion a little.


** With a tube amplifier, the effect can be very marked - since the voltage applied to the primary drops when a load is applied to the secondary.

The source impedance of a pentode or beam tube output stage is pretty high, triodes are somewhat better.

Only those amplifiers with large NFB ratios avoid the issue.


..... Phil

yep good point...

so it is very possible for a tube amp to have a bit less transformer saturation distortion when loaded compared to unloaded.

i.e. the distortion can go DOWN when loaded.


m