Re: OPT equalising circuit

Phil Allison wrote:
> 
> "Patrick Turneroid Raving Nut Case "
> > Phil Allison wrote:
> >>
> >> "Alex"
> >> >
> >> > I noticed that in most cases a capacitor or a RC circuit is
connected
> >> > across the primary of a tube OPT. It is apparently to compensate
for
> >> > the leakage inductance of the transformer.
> >>
> >> ** Partly for that  PLUS the fact that most speakers have a sharply
> >> rising
> >> impedance curve at high and supersonic frequencies.   A nominal 8 ohm
> >> speaker at 250 Hz can easily be 100 ohms at 50 kHz.
> >>
> >> > However, I am not sure how to correctly calculate this RC circuit.
> >>
> >> ** You are not alone ....
> >>
> >> > If I know my load impedance Rl,
> >>
> >> ** No you don't.
> >>
> >> You just know the  " nominal " impedance =  useless.
> >>
> >> What you need to make sure of is the amp does not break  into HF
> >> oscillations ( parasitic or continuous)  when there is no load  OR 
when
> >> under test with simulated ( or real ) speaker loads.
> >>
> >> The vast majority of tube amps have no need of such a compensation
> >> etwork  -  as the OT has little leakage and the NFB reduces to low
value
> >> at
> >> supersonic frequencies.
> >>
> 
> >
> > I don't know how many tube amps you have designed and or built or
> > repaired count. Many tube amps will oscillate at HF when connected
> > to a capacitor load.
> 
> ** Only a psychotic lunatic would deliberately connect a capacitor
across
> the output of a tube audio amp.
> 
>   The OP did not enquire about any such thing.
> 
> > In order to gain unconditional stability ....
> 
> ** An unnecessary,  pedantic,  pseudo technical wank.
> 
>  Snip rest of the Turneroid's hobby horse ride & public masturbation.
> 
> GOD  it is   BORING   !!!!

Well yes, Phil, I'm fucking boring alright.
I have lived a long life so far encountering lots of boring people
who complain I am so boring.
I have usually opened a door for them to allow them the pleasure 
of finding a less boring set of circumstances far away from me.


But if you wanna make an amp stable, you test with capacitors across the
output
secondary of the OPT.

Once the amp can withstand any value of C across the OPT sec when NFB is
used
then the amp is unconditionally stable because even with the extra phase
shift 
caused by the cap, the amp won't oscillate, ever.
 

But NEVER did I say you should test with C across the tubes.

C + R Zobel networks, sure, but never a pure C across any tube in the 
whole amp line up. When NFB is used, pure C just about always makes the 
amp MORE unstable.

Have you taken your medications today Phil?

Patrick Turner.




 
> .....   Phil