[R-390] 6082's and regulators

[Bob Camp]

Hi,

Hey, good data !!!

Here's what I *think* is going on.

    1) signal changes, drives AGC
    2) AGC goes to the mixer tubes
    3) Gain of the mixer tube changes
    4) Input impedance of the mixer tube goes up as the gain drops
    5) Oscillator load pulls

If that's the case then the next question would be which oscillator pulls
the worst. I would bet on the PTO being the one that moves the most but that
may only be crystal oscillator chauvinism ( alarm alarm - day job creeping
in to hobby echo - alarm alarm ).

    Take Care!

        Bob Camp
        KB8TQ



----- Original Message -----
From: "David Wise" <David_Wise@Phoenix.com>
To: "Bob Camp" <ham@cq.nu>; "Drew Papanek" <drewmaster813@hotmail.com>;
<r-390@mailman.qth.net>
Sent: Tuesday, January 07, 2003 4:45 PM
Subject: RE: [R-390] 6082's and regulators


> Question: How stable is the R-390A?
>
> Test setup: R-390A with ultra-regulated VFO
> filament, powered by external regulated B+
> supply via the main B+ fuseholder, with SE-3
> external BFO.  Receiver driven by HP 608D at 20MHz.
> (Too much work to extricate the 8640B from
> the bench it's on.)
>
> 608D frequency set for a few hundred Hz beat note
> on its calibrator heterodyne output.  SE-3 BFO set
> for almost the same note; actually a Hz or two off.
> SE-3 BFO set to the same "side" as the 608D
> calibrator, so generator drift affected both
> notes equally.  Listening to 608D on one side
> of stereo headphones, SE-3 on the other.
> With one note in each ear, they beat together
> in my brain.  I counted beats against a clock
> second hand while cranking the signal up and
> down, then the B+.
>
> I could have run the two heterodynes into
> a scope in "add" mode and timed the envelope
> peaks and valleys against the graticule, but
> I didn't think of it until just now.
>
> Signal from 3.5uV to 350mV (100dB).
> Result: About 5Hz.
>
> B+ from 210V to 220V.
> Result: About 1Hz.
>
> So the tuning is affected more by AGC than B+.
>
> I did not measure the oscillators independently;
> this is a system result based on the combined
> effects of the 2nd and 3rd oscillators.  They
> might both be drifting; if so, they drift almost
> exactly the same amount.
>
> I did not check the first oscillator or the BFO.
> The BFO is undoubtedly more sensitive than any of
> the conversion oscillators, since its screen voltage
> changes.
>
> No R-390As were harmed in the course of this experiment.
>
> 73,
> Dave Wise
>
> > From: David Wise
> > > From: Bob Camp [mailto:ham@cq.nu]
> > > Can you even measure a change in the supply voltage as you
> > > tune a signal and
> > > if so how much?
> >
> > I'm sure you can.  As signal strength varies, so does the
> > AGC and consequently the RF amp, mixer, and IF amp cathode
> > currents, which make up a respectable fraction of the
> > unregulated B+ load.
> >
> > I'll report back with hard data.
> >
> > This isn't the only source of frequency variance.
> > AGC on the mixers causes small changes in their
> > dynamic interelectrode capacitances, which reflect
> > back to their respective oscillators.  I didn't
> > say these are large effects, just that they exist.
> > There's a fascinating section on this phenomenon
> > in the Radiotron Designers Handbook.
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