[AMRadio] RE: Another receiver update...

[russ dworakowski]

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
>
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