GerryE123 wrote:
>
> "Patrick Turner" <info@[EMAIL PROTECTED]
> wrote in message
> news:481DED13.3F4D42A4@[EMAIL PROTECTED]
> > The whole business of an IST is difficult.
> >
> > The parafeed I mentioned above is the best I have used,
> > wide BW, with slight shelving of response at LF and HF,
> > and no added iron cause distortions at any F.
> >
> > One can also use a µ-follower which also works well,
> > or use a pentode for the dc anode supply with extremely high AC
> > impedance.
> >
> > I like the parafeed choke plus R method because it works, and sounds
> > well,
> > and has electronic simplicity of elements, even though
> > you would need a choke with 25mm square core section and have
> > 7,000 turns of fine wire, and just the right gap size.
>
> A belated THANK YOU to Patrick (I was hoping you would respond) and
everyone
> else who replied! I know that interstage transformers are a well known
> design option, I just thought it was interesting to read a manufacturers
> deatiled explanation for using it as opposed to other specific choices.
>
> Jim Hagerman is coming out with a new and unusual 2A3 amp. Here's a
quote
> from it's description:
>
> "Distortion is exceedingly low, especially given the fact that no
feedback
> is used, thanks to the harmonic cancellation of the output stage, which
> operates partially in both single-ended parallel and push-pull
differential
> modes. This balance results in SET-like musicality yet with PP control
and
> dynamics."
>
> Here's the link to the manufacturers web page for the new amp:
>
> http://www.haglabs.com/pa10.html
>
> What do you think? Thanks.
>
> Gerry
Sun Corp made an almost identical amp many years ago.
I repaired a pair last year.
The IST had a gap for the DC through the primary of the IST.
The above amp uses a CCS and cap couples the IST primary, which means
that
an un-gapped IST can be used, and if the core material is good, THD
should be lower
and BW wider because of fewer turns needed to get sufficient primary
inductance.
One could do the same with any SE output stage, but the CCS must come
from a voltage source
equal to about twice the Ea of the tube to allow the swing upwards of
anode signal.
So you'd have say 400V at 60mA floe in a CCS at idle, which is 24 watts,
and the same as the Pd of the tube.
So you never see the CC done like this for any SE amp.
A choke is used instead.
And the magnetic stored energy allows the positive rise in signal
voltage as the tube
is turned off by a negative goingf grid.
Its a case of turning something off and getting something more,
yet another thing that defies ordinary human common sense.
Patrick Turner.
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