[R-390] No Peak on T701

[Barry]

They have 510pF, 2%, but they don't stock this and have a minimum quantity
of 50.  I can get a 5%, but would like to stick to spec if possible.

Thanks!

Barry - N4BUQ


----- Original Message -----
From: "Jim M." <jmiller1706 at cfl.rr.com>
To: "Barry" <n4buq at knology.net>; <r-390 at mailman.qth.net>
Sent: Sunday, April 30, 2006 2:19 PM
Subject: Re: [R-390] No Peak on T701


> www.mouser.com
> takes small orders.
>
>
> ----- Original Message -----
> From: "Barry" <n4buq at knology.net>
> To: <r-390 at mailman.qth.net>
> Sent: Sunday, April 30, 2006 3:07 PM
> Subject: Re: [R-390] No Peak on T701
>
>
> > I'm seeing about 1.8V peak-to-peak, unterminated into my 'scope.
> >
> > The more I think about this, the more I'm wondering if C709 might be
bad.
> > Wouldn't this cause low output?  It's spec'd as a 2% so I'm thinking if
it
> > has changed, even slightly, it might be causing a problem.  If I recall,
> > C327 (the cap across L230/T207) is of the same type and it has been
known
> > to
> > cause low output from the 1st crystal oscillator.
> >
> > I haven't found a 510pF, 2% cap yet, though.  :-(   Surplus Sales of
> > Nebraska has them, but they also have a $10 minimum order and I really
> > don't
> > need anything else from them right now.  Any sources, anyone?
> >
> > Barry - N4BUQ
> >
> > ----- Original Message -----
> > From: "Tim Shoppa" <shoppa_r390a at trailing-edge.com>
> > To: <shoppa_r390a at trailing-edge.com>; <r-390 at mailman.qth.net>;
> > <n4buq at knology.net>
> > Sent: Sunday, April 30, 2006 6:47 AM
> > Subject: Re: [R-390] No Peak on T701
> >
> >
> >> "Barry" <n4buq at knology.net> wrote:
> >> > I've been doing some more tweaking on one of my R390As.  T701 (output
> >> > transformer from the PTO) will not peak.  I'm getting slightly less
> >> > then
> > 2V
> >> > peak to peak no matter how I adjust the slug.  Anyone ever seen this
> >> > behavior?  If so, any ideas what's wrong?
> >>
> >> 2V RMS is not awfully low. When I scope the PTO output I see 6-8V
Pk-Pk,
> >> the max in the middle of the range and falling off towards the edges
> >> (especially the high freq/low counter edge). This is the
> >> raw unterminated PTO output; putting a 50-ohm terminator on it
> >> drops the value by a little more than a factor of two.
> >>
> >> Let's see, 6V Pk-Pk is a little above 2V RMS. Maybe your PTO output
> >> is a little bit low but I can't say that it's "bad".
> >>
> >> It's been a while since I screwed around with it but IIRC there
> >> was not a lot of variation to be had by swapping PTO tubes around.
> >> (I was mostly looking for frequency stability not PTO output
> >> level as I swapped tubes around.)
> >>
> >> I seem to recall past postings on this list that suggested that
> >> the PTO output network was there to "squash" any resonances and
> >> make the output roughly flat across the PTO range. So actually
> >> peaking it up for one particular frequency may be not good (may
> >> in fact be impossible!)
> >>
> >> As another data point, most of my crystal oscillator band outputs
> >> are in the 8 to 10V Pk-Pk range, with some going up to 12 or 13V
> >> and a few bands as low as 5 or 6V (I guess the variations are
> >> due to crystal activity or just the way picking off the harmonics
> >> works; the units have been peaked up on each band.)
> >>
> >> Getting back to my mixer design obsession, I guess this means
> >> that most of the mixers were designed with LO inputs in the
> >> range of a few (1-3?) volts RMS in mind and that a factor of two
> >> variation in level throughout the frequency range is not out of
> >> design specs.
> >>
> >> I'm not claiming that my values are golden reference standards
> >> either, just what I see on my two 390A's. Is there an official
> >> output level that the PTO is supposed to meet? And is that
> >> value into a terminator or not?
> >>
> >> Tim.
> >>
> >
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