[AMRadio] RE: Another receiver update...

[Brett Gazdzinski]

Bacon,
Its possible I could install a small filament transformer
and have it powered all the time...the 6j5 is only .3 amps I think.

I also thought of RF chokes as soon as you pointed out the cathode was above
RF ground.

2kc after 10 minutes is not bad, but that sort of depends on the
particular 6j5 I use, so I would like to try some things
so as to be able to use any 6j5 tube there.

I will try the RF chokes...

The receiver is really working well, last night I listened
to 80 meters, conditions were quite weird, with fast flutter,
and long skip, and I heard stations in New England working
w5 stations in Texas, and I could hear both sides quite well,
100% copy plus, while they had a rough time copying each
other, likely due to the added distance between them,
but the home brew receiver did a fine job pulling
everything out.
It still strikes me as odd that the receiver seems to work better
than the r390a I have (yes its been aligned)....


The next project is a home brew exciter.
Since I have two big rigs to drive, I figure I will actually
make two separate output stages, so I can tune one up on
80, the other on 40, and run different (pre set) power outputs.
That way, I wont have to tune anything when going between
80 and 40 meters except for the frequency...

A pair of 6146's, one for each rig should do nicely....

I found a nice national dial on ebay, but some scum outbid
me at the last moment!

Matching dials would be the cats meow!
Or maybe I should think about a digital readout for both
the receiver and the exciter....
I think kits are available to do this...


Brett
N2DTS



>
>
> 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
> > >
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