[R-390] The Penultimate R-390* Ballast Replacement

[Bruce Hagen]

Hello:

Yes, that makes sense. Only own one 390 so not a problem for me.

Thanks,

Bruce


----- Original Message ----- 
From: "Bob Camp" <ham at cq.nu>
To: "Bruce Hagen" <bhagen at msn.com>; "R-390 HF Receiver List" 
<r-390 at mailman.qth.net>
Cc: <ToddRoberts2001 at aol.com>; <ToddRoberts2001 at aol.com>
Sent: Sunday, February 13, 2005 11:03 AM
Subject: Re: [R-390] The Penultimate R-390* Ballast Replacement


> Hi
>
> The tube swap process works fine as long as all of your radios have the
> same mod in them. The problem comes when you blindly swap modules
> between a ballast tube radio and a 12 volt filament radio.
>
> Take Care
>
> Bob Camp
> KB8TQ
>
>
> On Feb 13, 2005, at 4:28 PM, Bruce Hagen wrote:
>
> > I find myself somewhat mystified with all of the ballast tube
> > solutions.
> > Most very clever and well thought out but were am I missing it? It
> > seems to
> > me that an inch or so of wire bent into a "U" shape for the ballast
> > and then
> > pulling two 6.3 volt tubes and replacing them with two readily
> > available and
> > cheap 12.6 volt tubes is the logical and easiest solution if you do
> > not want
> > to spend a few dollars and buy a 3TF7. Bruce
> >
> >
> > ----- Original Message -----
> > From: <ToddRoberts2001 at aol.com>
> > To: <r-390 at mailman.qth.net>
> > Sent: Sunday, February 13, 2005 9:54 AM
> > Subject: Re: [R-390] The Penultimate R-390* Ballast Replacement
> >
> >
> >> Most of the 3TF7 substitutes I have read about involve buildng
> >> something
> >> small enough to plug directly into the 3TF7 socket or on a nearby
> >> bracket.
> >> This
> >> comes with problems of heat dissipation or else installing unsightly
> >> brackets
> >> near the I.F. subchassis. Some of the recent ideas got me thinking -
> >> Why
> >> not
> >> build a small separate power supply module with a
> >> well-regulated/filtered/bypassed 12.6 VDC output that could be placed
> >> next
> >> to the receiver and the only
> >> connection would be a small umbilical cable with a 9-pin plug that
> >> plugs
> >> directly
> >> into the 3TF7 socket? You could run the umbilical through the side of
> >> the
> >> R390A
> >> chassis thru one of the large holes and tuck the power supply and
> >> cord out
> >> of
> >> the way next to the receiver. This layout is similar to the way some
> >> audiophile preamps use a separate power-supply module with an
> >> umbilical.
> >> You could
> >> modify one or two pins of the 3TF7 socket with a jumper to ground to
> >> provide a
> >> ground return for the 12.6VDC so you wouldn't have to tie down a
> >> separate
> >> ground
> >> lead with a terminal and screw somewhere else on the chassis. When you
> >> plug
> >> in the umbilical it breaks the 25.2 VAC circuit and connects the
> >> 12.6VDC
> >> circuit and ground. The ground pins would have no effect on the
> >> original
> >> 3TF7 if you
> >> wanted to plug one back in.  This way you could build a nice little
> >> husky
> >> separate  regulated/filtered/bypassed 12.6 VDC power supply and not
> >> have
> >> to
> >> miniaturize it or compromize the performance. If you want to go back
> >> to a
> >> 3TF7 just
> >> unplug the DC supply 9 pin plug and put the 3TF7 back in. No unsightly
> >> permanent wires or brackets hanging off the I.F. subchassis.  The
> >> regulated DC
> >> supply should give the ultimate in stability and pure DC on the
> >> filaments
> >> of the
> >> BFO/PTO tubes. 73 Todd WD4NGG
> >> _____________________________________________________________
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