Larry,
One of mine did the same. There were several things done. First both the
1625, and 1626 were low on emission. Put the variac on the 458 AC cord, and
the VFO would shift significantly when the line voltage was lowered just a
little bit. Further
inspection showed the 1626 filament at about 14 VDC, and anything less,
would cause the output to drop, and the frequency to shift. A new 1626 fixed
that nicely. I also added some series resistance to run the 1626 filament at
12 volts instead of 14. Similar story on the 1625. I just replaced it, and
the AC filament voltage was OK with this tube.
I still had low output on 40 meters however. Sure you must peak the 1625
plate capacitor for exact resonance (requires a screwdriver through the
side). The 3 coils added to the 1625 plate tank go to the band switch, and
the common wiper goes to AC ground through a .001 Uf capacitor. On my bad
458, this was a ceramic disc capacitor. I replaced it with a silver mica,
and the closest value I had was 2200 pf (.0022 uf). The VFO output on 40
meters (when the 1625 triples) increased significantly, and I can almost,
but not quite, run the 80 meter output power on 40 meters.
For 10 meters you need 38 Mhz for 29 Mhz operation (38-9=29). You need
the
10 meter VFO option for that. I have a schematic in .GIF format should
anyone want it. I have one, and it works well. Problem is, I need to do the
CE mods to the 6BA7 converter, and 12BH7 cathode follower to make this fly.
My 20's (2) are both early models.
On my 20A I am getting 45 watts carrier on 80 meters when using the 7591's
in the final with 570 volts on the plates. I have recently gone through
another round of repairs, and such, and haven't ventured off 80 meters to
see how the other bands work.
I got the VOX working last night, and all the old electrolytic capacitors
have been replaced. Several were open, and were doing nothing except
occupying space. I should have done that 2 years ago. The caps open had a
"guaranteed for 1 year" logo on them. I guess 50 years is pushing my luck!
Hope this helps.
Regards,
Jim
WD5JKO
> -----Original Message-----
> From: [EMAIL PROTECTED]
> [mailto:[EMAIL PROTECTED] Behalf Of Larry Szendrei
> Sent: Friday, January 03, 2003 9:12 PM
> To: [email protected]
> Subject: Re: [AMRadio] "Reply" button got me...
>
>
> Mike et. al.,
>
> My CE20A has about 1/2 the output on 40M as it has on the other bands
> (160, 80, 20, & 15) in spite of the fact that the CE mods to cure this
> in the VFO-458 have been implemented. As I recall the VFO output is
> tripled for 40M, and only doubled or on the fundamental for the other
> bands. My VFO doesn't have 10M capability, so have no experience with
> 10M on this rig.
>
> 73,
> -Larry/NE1S
>
> MIke Wells wrote:
> >
> > I'm enjoying the 20A discussion. I have a 20A that I want to
> get on the air
> > so keep the messages posted here for the benefit of others.
> >
> > Tell me more about the VFO, are you having good luck with it on
> all bands?
> > I've only got mine working on the low bands, no oscillation on
> 40 meters.
> > Suggestions?
> >
> > 73,
> >
> > Mike W0FD
> >
> > Subject: [AMRadio] "Reply" button got me...
> >
> > Regarding the previous posting to the list: it was unintended. The old
> > "reply" button got me again!
> >
> > If you're interested, read it. It's part of a discussion Jim Candela and
> > I are having about a vintage SSB exciter, the venerable Central
> > Electronics 20A. If not, the "Delete" button is much more predictable in
> > its effects than "Reply." :>)
> >
> > 73, and back to AM...
> >
> > -Larry/NE1S
> >
> > _______________________________________________
> > AMRadio mailing list
> > [email protected]
> > http://mailman.qth.net/mailman/listinfo/amradio
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