[AMRadio] Class AB and B audio XFMRS

John E. Coleman (ARS WA5BXO) wa5bxo2005 at pctechref.com
Mon Mar 13 13:02:04 EST 2006

	Perhaps I should clarify one point that we may all be forgetting
here.  A XFMR will only transfer energy during the movement of the magnetic
field (EXPANDING OR CONTRATING).  If the magnetic field becomes stationary
then no energy will be transferred to the secondary regardless of the amount
of iron.  But if the magnetic movement is fast enough then transfer
efficiency can be high.  As the frequency is lowered the magnetic movement
is slowed down then the efficiency drops off.  I'm not sure if this is the
proper term mathematically but it is as if the coefficiency of coupling is
not as good when the frequency becomes too low.

	I hope I'm not boring folks with this and some may say I am making a
mountain of a mole hill.  I just find it fascinating.  I guess it is just my
type of thing.

John, WA5BXO      
----Original Message-----
From: amradio-bounces at mailman.qth.net
[mailto:amradio-bounces at mailman.qth.net] On Behalf Of John E. Coleman (ARS
Sent: Monday, March 13, 2006 11:36 AM
To: 'Discussion of AM Radio'
Subject: RE: [AMRadio] Class AB and B audio XFMRS

The Band pass and energy Xfer of a transformer with no load is one thing but
it all changes depending on the load and the DC involved.  In class A
balanced PP circuits the XFMR will still saturate at some frequency and load
even if it is perfect balance on the PP circuit.  XFMR saturation distortion
in class A single ended service has a trapezoidal shape if the quiescent
current is too high but in PP class A the shape is weird because the XFMR
remains balance as for as DC is concerned but yet the XFMR will not produce
the sign wave on the output if the frequency is too low.  It resembles cross
over distortion even though there is no cross over in class A push-pull.

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