[AMRadio] Class AB and B audio XFMRS


John E. Coleman (ARS WA5BXO) wa5bxo2005 at pctechref.com
Mon Mar 13 12:35:48 EST 2006


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.

My suggestion is to watch for this type of thing by using a audio signal
generator.  While on the air (DUMMY LOAD) slowly sweep down on the audio
frequency generator, at some point (probably between 10 and 100 CPS) the
output will become distorted.  Design the preamps and drivers low frequency
roll-off to be at or before this distortion happens. 

John, WA5BXO      



-----Original Message-----
From: amradio-bounces at mailman.qth.net
[mailto:amradio-bounces at mailman.qth.net] On Behalf Of W5OMR/Geoff
Sent: Sunday, March 12, 2006 10:43 PM
To: Discussion of AM Radio
Subject: Re: [AMRadio] Class AB and B audio XFMRS

John Coleman ARS WA5BXO wrote:

How difficult would be it be 'sweep' the mod iron?

The reason I ask, is because so much of the surplus stuff we get is 
still of Mil-Spec design.  Therefore, if the mil-spec transformer says 
it's freq response is +/- 1db from 100Hz ~ 3000Hz, how would one 
determine exactly what this particular peice of iron will be capable of 
handling, in the 'non-comercial' application?

--
73 = Best Regards,
-Geoff/W5OMR


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