[AMRadio] push pull output XFMRs and neg feedback

Jim Candela jcandela at prodigy.net
Wed May 20 19:41:36 EDT 2009

Message: 4
Date: Mon, 18 May 2009 19:16:10 -0400
From: John Coleman <jc at pctechref.com>
Subject: Re: [AMRadio] push pull output XFMRs and neg feedback
To: Discussion of AM Radio in the Amateur Service

        I had a chance to add the 3300 ohm resistor and the .001uf capacitor to the circuit at the grid of the phase splitter but it did not help or if it did it was negligible.  The oscillation is at 8000 to 10000 cps.  I think I had originally said 18000 but the scope says different and it is audible even for an old smell like me.  BTW I don't have any pre-emphasis or de-emphasis in the FB path it is strictly a resistive pad.

I'll be running some test soon and will let you know the results.

BTW the output XFMRs are Thordarson 22S63  5000 ohm ptp primary --  8 and 16 ohm secondary --  rating 40 watts

John Coleman, WA5BXO


Reply by Jim, WD5JKO:


    Sounds like a lot of fun! I think if I was having feedback oscillations like that, I would revert to zero feedback and see how that goes. Maybe something else is going on. Hopefully you will find something. Apply the feedback later.

Good Luck!

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