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items: The Introduction of Push - Pull Theory
items: Re: The Introduction of Push - Pull Theory

The Introduction of Push - Pull Theory
type: item
description: During a heated "PP" debate on another forum, I tried to describe PP-model in a simplified way. I finally put together and extend some posts of mine about that subject. Enjoy! THE INTRODUCTION OF PUSH - PULL THEORY 1. FOREWORD: We`d introduce some simplifications - the transformer is ideal (no losses, the effects of Rw, Lp, Cw, etc. are negligible, tubes are identical and "expressed" as AC generators/voltage sources with their internal resistances, the effects of non-linearity is negligible (rp and mu are constant), speaker load is resistor, etc. We`ll neglect DC conditions, too. 2. SINGLE ENDED (SE) OUTPUT STAGE We have output transformer with N1=300 turns on the primary, and N2=10 turns on the secondary. The turns ratio n=N1/N2=300/10=30. If we connect the speaker of Rs=4 Ohms on the secondary, then our tube, connected at the primary "see" the load Rpr=(N1/N2)^2*Rs=30^2*4=3600 Ohms. Our tube/AC generator has mu=3,75, rp=700 Ohms and with Ugk=32 Vrms "input" our Ugen=mu*Ugk=3,75*32=120Vrms, then current that flows through the circuit (rp and Rpr in series) is I=120/(3600+700)=27,9mA, and the voltage drop across rp is Urp=700*0,0279=19,5Vrms - then voltage through our Rpr is 100,5Vrms. Note that the conditions are similar to the "ideal" 2A3 or 300B tube, working on the linear part of its anode characteristics. From now on, we`d simplify things even more - we`ll neglect our internal tube/generator resistance, and just say that our generator 2gives" 100vrms across the 3600 Ohms resistance. Then power at the primary is: Ppr=Upr^2/Rpr=100^2/3600=2,77W. The AC current through primary load is Ipr=Upr/Rpr=(Ppr/Rpr)^0,5= 27,77mA. Our speaker, connected at the secondary gets this power, or Ppr=Ps, voltage on the speaker Us=Upr/n=100/30=3,33Vrms, and current Is=Us/Rs=(Ps/Rs)^0,5=Ipr*n=0,833A. See the schematic Nr.1. If we have another secondary, again with N3=N2=10 turns, and connect them in a series, then: (see the schematics Nr.2) -we can connect Rs=4 Ohms speaker across on…
creator: Damir
date: 2004-12-30T19:05:10-00:00

Re: The Introduction of Push - Pull Theory
type: item
description: Excellent post, thanks!
creator: Wayne Parham
date: 2004-12-30T19:19:58-00:00

Re: The Introduction of Push - Pull Theory
type: item
description: looks correct to me.
creator: metasonix
date: 2004-12-31T04:40:21-00:00

Re: The Introduction of Push - Pull Theory
type: item
description: Thanks Damir; O'kay to print and save your work? As a neophyte seeing this stuff breadboarded makes it much easier to follow. Although lots of work for teacher.
creator: Manualblock
date: 2004-12-31T16:16:04-00:00

Re: The Introduction of Push - Pull Theory
type: item
description: OK to save/print? Of course, my intention is to give the informations for free ("open source" or so:-)), and avoid teacher/guru/magic vs. scholar as much as possible (sometimes present in this hobby :-)). I received much, and it`s fair to give a little... Sorry for some typing errors. All the best to everyone, happy New Year!
creator: Damir
date: 2004-12-31T18:55:14-00:00