It's an LM7812 on a decent size heat sink standing up on the board.
David Robbins K1TTT
e-mail: mailto:k1ttt@arrl.net
web: http://www.k1ttt.net
AR-Cluster node: 145.69MHz or telnet://dxc.k1ttt.net
> -----Original Message-----
> From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com] On
> Behalf Of David Cutter
> Sent: Tuesday, December 09, 2008 23:05
> To: k1ttt@arrl.net; amps@contesting.com
> Subject: Re: [Amps] Fwd: rx noise?
>
> Fascinating stuff. I couldn't find a reference to exactly what regulator
> is
> used. 7812 or variable regulator?
>
> David
> G3UNA
>
>
> ----- Original Message -----
> From: "David Robbins K1TTT" <k1ttt@arrl.net>
> To: <amps@contesting.com>
> Sent: Tuesday, December 09, 2008 10:50 PM
> Subject: Re: [Amps] Fwd: rx noise?
>
>
> > p.s. as I noted in my blog I have heard similar wandering birdies before
> > but
> > never had them land on a band like that one did during cqww. I have
> been
> > doing other repairs on those amps so they have moved around from band to
> > band periodically, its possible that amp has been oscillating for a
> while
> > and it just never got caught... add in temperature sensitivity and
> > apparently some line voltage sensitivity and it may have just been hot
> > enough and the voltage at just the right spot that day. As I said, when
> I
> > tried to reproduce it I could only get it in the 20m band for a short
> > time,
> > most likely it was drifting all over the place.
> >
> >
> > David Robbins K1TTT
> > e-mail: mailto:k1ttt@arrl.net
> > web: http://www.k1ttt.net
> > AR-Cluster node: 145.69MHz or telnet://dxc.k1ttt.net
> >
> >
> >> -----Original Message-----
> >> From: d.cutter@ntlworld.com [mailto:d.cutter@ntlworld.com]
> >> Sent: Tuesday, December 09, 2008 10:33
> >> To: Ian White GM3SEK; amps@contesting.com
> >> Subject: Re: [Amps] Fwd: rx noise?
> >>
> >> Did the regulator have proper bypass in the first place or was this a
> >> problem just waiting to pop out? Capacitor-to-regulator distance is
> >> critical. I've never known a regulator go funny if it was properly set
> >> up
> >> in the first place. As Pease would say "do what the manufacturer tells
> >> you or all bets are off."
> >>
> >> David
> >> G3UNA
> >>
> >> >
> >> > From: Ian White GM3SEK <gm3sek@ifwtech.co.uk>
> >> > Date: 2008/12/09 Tue AM 08:39:07 GMT
> >> > To: amps@contesting.com
> >> > Subject: Re: [Amps] Fwd: rx noise?
> >> >
> >> > David Robbins K1TTT wrote:
> >> > >I think the noise in that one is solved... take a look at the scope
> >> > >pic
> >> > >for a 12v regulator with a 2v p-p oscillation on it at:
> >> >
> >>
> >http://wiki.k1ttt.net/2008%20Maintenance%20and%20Upgrade%20Blog.ashx?NoR
> >> > >edir ect=1#Bottom That's one repaired, another one tested clean for
> >> > >now, and 5 more to go.
> >> > >
> >> > Glad you found the problem, Dave. By coincidence(?) someone recently
> >> > found a similar problem with a 78xx in a GaAsFET preamp that had been
> >> > OK
> >> > for years, but then decided to become unstable.
> >> >
> >> > Any thoughts about what changed to trigger the instability? (Aside
> from
> >> > it being CQWW weekend, and the regulator having poor stability
> >> > margins.)
> >> >
> >> >
> >> > --
> >> >
> >> > 73 from Ian GM3SEK
> >> > http://www.ifwtech.co.uk/g3sek
>
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