[AMRadio] Class AB and B audio XFMRS


W1EOF w1eof at hamnutz.com
Mon Mar 13 15:08:30 EST 2006


Good points about the complex relationship of the components making up a
transformer. I especially liked the reminder about the bia used on recording
heads... I had completely forgot about that.

73,

Mark W1EOF

> BTW audio analog tape recorders minimized this problem with the head
> by using a high frequency bias, say 22 kcs, to keep the flux
> constantly changing and allowing good LF response while making the
> recording.  The HF signal is filtered out on playback either by the
> playback head or immediately before the first preamp.
>
> Larry W3LW
>
> Some folks on here surely can amplify this and correct my fuzzy
> memory if needed.
>
>
> The problem is the energy transfer medium - THE IRON.
>
>
>
> At 01:02 PM 3/13/2006, John E. Coleman (ARS WA5BXO) wrote:
> >         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
> >WA5BXO)
> >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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