[R-390] R-390 Related Activities

[Tom Warren]

Tom,

I'd sure like to hear more about your experience with aligning the 390A with
the sweep generator.  Moving the LC passbands over to the the crystal filter
center frequency will not make a difference as to sound quality since
presumably you mean the sound quality when listening to an AM or SSB signal
in the 2, 4, 8, or 16kHz bandpass mode when the cryslal filter is not being
used.  HOWEVER, moving the LC passband to center on (say) the 8kHz filter
and then fussing with the LC passband to get better passband symmetry
throughout the whole IF strip indeed should make a good bit of difference.
On one of Chuck's tapes (the ones I just sold), he talks about using an
audio distortion analyzer on the output of the AF deck to then tune the
IF-LC filters to then minimize the distortion.  Presumably he is linearizing
the phase response of the IF-LC-Mech Filter bandpass as best possible and
thus reducing the distortion.  My very limited experience is that there's
lots of ripple (no pun intended with Chuck) (like 1.5-2.5dB) over the
passband of the Mech Filters and I'm terrified to think what the phase
response is through the IF strip.  Not good is the first answer supported by
the passband amplitude ripple.

So bottom line is that I'm interested in your experience with the sweep
generator method of alignment.  I'm just now getting my two 390A's (my
pristine EAC'67 and a depot dog, mostly Motorola) up to electrical
specification (many, many capacitor, IF can, Mech Filter, and resistor
replacements later) so that maybe I can take on some of the nuances of
alignment.  So far alignment has yielded over 23-25dB SNR (Roger Ruszkowski
likes at least 20 dB) at 4 microvolts input over the entire 32mHz frequency
range (oh well, the top two bands are a bit weaker, but who the heck listens
to anything there anyhow?).

Best,
Tom, W4PG

----- Original Message -----
From: "Tom-WB3AKD" <wb3akd@arrl.net>
To: "R390 (E-mail)" <R-390@mailman.qth.net>
Sent: Friday, January 10, 2003 9:07 AM
Subject: [R-390] R-390 Related Activities


>
> Probably no news for most of you here but having done the "manual" IF
> alignment some time ago and having the sweeper hooked up, I muscled the
390
> over to the bench and swept it.  I found the shapes to be unsat so went
> through the procedure with the sweeper:  Moved the LC pass bands over to
> where the crystal filter was centered then tweaked the shapes up a bit.
> Much nicer sound now.  I am now fully sold on the sweept procedure.