[R-390] SP600JX17 - drift

Wed, 09 Jan 2002 19:09:01 -0500

I suppose this really belongs on the Hammarlund list, but here's my 2 cents
worth anyway:

As heavy as the SP-600's are, the chassis are not all that solid.  If you've
ever picked one up wrong, you may have noticed that they can twist a bit.

In addition to the "brace" on that tube shield (why all the quotations
marks, Rod?), there are possibly some other sources of drift as the receiver
warms up, or from vibration.  For example, the RF strip is right over the
turret with all those spring contacts.  If something is loose or that strip
is missing some screws, I suppose that could be a factor -- and lead dress
under there after a repair or recapping job.

Also, the gauge of the sheet metal is not quite as thick as that with the
'390x's which also benefit from the H-frame/modular design.  Even the front
panels on the SP-600's are thinner -- from the half dozen I've seen.

The chassis has six heavy-gauge corner supports -- don't know what else to
call them -- which should be good and tight.  Many of these rx's are missing
their bottom covers -- a medium gauge rectangle of aluminum with six holes
for the screws that mount up to the ends of those supports.  The chassis is
a lot stiffer with the cover in place.  (Hank Arney may still have repro
covers available).

Just theorizing, but it stands to reason, if that tube shield with the brace
is important, then some of the bigger parts underneath it might be too.

Barry

----- Original Message -----
From: "Rodney Bunt" <[email protected]>
To: <[email protected]>; <[email protected]>
Sent: Wednesday, January 09, 2002 6:26 PM
Subject: Re: [R-390] SP600JX17 - drift

> Chuck,
>
> The 6C4 Oscillator at V4 is "braced" to the the chassis with a "thumb"
screw, "brace" and "sheild"
> combination.
>
> If you move this tube the oscillator frequency moves.
>
> I have seen this tube shield and "brace" arrangement replaced with "heat
dissipating tube shields"
> without this "brace" arrangement.
>
> This is not recomended, unless the "mechanical stability" of the "Brace"
is reinstated somehow.
>
> This also is a potential source of "drift" before "warm up" has
stabalised.
>
> Rodney
> VK2KTZ
>
>
> --- Chuck Rippel <[email protected]> wrote:
> > One thing to keep in mind is that SP-600's, even after recapping and
taking
> > the extra step of adding the mod which regulates the filament voltage to
the
> > top 4 tubes, still drift quite a bit until the entire chassis heat
saturates.
> >
> > As to setting the input line voltage, the best way to determine the
correct A/C
> > Line input voltage (@60 cycles!!!!!) is to monitor the tube filament
voltage at
> > your tube of choice other than the rectifier, regulator or the
(12AU7??).   Set
> > the line input voltage to a value that yields 6.3VAC at the tube
filaments.  That
> > puts the other voltages right about where they need to be.
> >
> > > > << PS: if the input volts are too high, then the 0A2's get very hot,
> > and very
> > > > bright !!! No wonder  they drift, and stop regulating....
> >
> > > > Rodney
> > > > VK2KTZ >>
> >
> > -----------------------------
> > Chuck Rippel, WA4HHG
> > R390A List Co-Administrator
> > Reply to: [email protected]
> >
> > To learn more about R390A's visit:
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> >
> >
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> > 1967 Contract EAC R390A #2808 with outboard Sherwood SE-3 Sync. Detector
> > 1967 Contract EAC R390A #5295
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> > 1967 Contract EAC R390A #1023
> >
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