[AMRadio] RE: Another receiver update...

[Bob Bruhns]

Hi Brett,

On my VF-1, I ran the 6AU6A filament all the time, although I had it
on reduced voltage when the unit was off.

I didn't do this, but you might float the 6J5 filament leads with
some kind of RF chokes, and RF-bypass them to the cathode.  Consider
any DC drop to the filaments and any heat in the chokes when doing
this, though.

  Bacon


----- Original Message -----
From: "russ dworakowski" <wb3fau at hotmail.com>
To: <amradio at mailman.qth.net>
Sent: Wednesday, February 27, 2002 11:47 AM
Subject: RE: [AMRadio] RE: Another receiver update...


> Hey Brett,  you can use a separate  filament transformer  for the
6J5
> and  leave it running  all the  time.  That will  solve the  warm
up
> problem.  Russ
>
>
> >From: Brett Gazdzinski <brett.gazdzinski at wcom.com>
> >Reply-To: amradio at mailman.qth.net
> >To: amradio at mailman.qth.net
> >Subject: RE: [AMRadio] RE: Another receiver update...
> >Date: Tue, 26 Feb 2002 20:36:51 -0500
> >
> >Bacon,
> >I think you are right on the money.
> >Looking at the oscillator design I used, the cathode is
> >above ground for rf, but the filament is bypassed to ground.
> >(RF choke to ground)
> >
> >There is another way to do it with a grounded cathode,
> >I found a good design in the October 1957 QST, but it
> >would require a lot of changes, the tuning cap
> >has to come off ground along with the coil.
> >
> >I am not sure I want to start over with making coils,
> >trying caps, etc, so I will see how it acts with the NPO
> >caps.
> >As it is, with the glass 6j5 in there, it drifts
> >about 2 kc from a cold start...
> >Not unreasonable for a home brew receiver, I just need to
> >let it warm up for 10 minutes before its accurate...
> >
> >Thanks for the tip,
> >Brett
> >N2DTS
> >
> >
> > >
> > > Hi Brett,
> > >
> > > I once read about internal cathode interface resistance in
> > > oxide-cathode vacuum tubes.  Evidently the various layers of
> > > the cathode can make intermittent internal contact, and this
> > > can cause frequency shifting and drift.
> > >
> > > Try adding a low value resistor in series with the cathode,
> > > maybe a few hundred ohms to 1.5K or so, and see if it
> > > helps...  assuming it does not stop oscillation altogether!
> > > I did this with the 6AU6A in my Heathkit VF-1, and it helped.
> > >  But I still had to select tubes for best performance.
> > >
> > >   Bacon, WA3WDR
> >
> >_______________________________________________
> >AMRadio mailing list
> >AMRadio at mailman.qth.net
> >http://mailman.qth.net/mailman/listinfo/amradio
>
>
> _________________________________________________________________
> Get your FREE download of MSN Explorer at
http://explorer.msn.com/intl.asp.
>
> _______________________________________________
> AMRadio mailing list
> AMRadio at mailman.qth.net
> http://mailman.qth.net/mailman/listinfo/amradio