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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