Re: OPT equalising circuit

On Sat, 3 May 2008 10:08:10 +1000, "Phil Allison"
<philallison@[EMAIL PROTECTED]
> 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.

Try measuring the capacitance of a loudspeaker.

>
>  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   !!!!
>
>
>
>
>.....   Phil 
>